Scientific Blog Article

Regulatory Considerations Regarding Sunscreen Actives

Yun Shao
Kobo Products, Inc.
June 2024

Summer is here, and it is time to enjoy outdoor activities and the beautiful landscape with friends and family. However, the Sun is bright and scorching, making the weather hot and the use of sunscreen essential. Sunscreen, sunscreen, sunscreen!

When developing sunscreen products, it is crucial to focus not only on performance and aesthetics to meet consumer expectations but also on regulatory compliance. Sunscreen products are regulated worldwide and are classified as drugs by the FDA. For the US market both the manufacturers of sunscreen products and the actives (considered as Active pharmaceutical ingredients (APIs)) used in these products must comply with FDA requirements, including registration and listing, as well as adherence to ICH Q7A Current Good Manufacturing Practices.

In terms of quality control, all sunscreen actives must meet the United States Pharmacopeia (USP) specifications mandated by the FDA in its sunscreen monograph.¹ However, there can be some confusion regarding the specific details of these requirements.

National Drug Code (NDC)

The NDC, or National Drug Code, is a unique 10-digit, 3-segment number that serves as a universal product identifier for human drugs in the United States. This code is present on all nonprescription (OTC) and prescription medication packages and inserts in the US. Most formulators know that an NDC is required for a finished sunscreen product. But what about the sunscreen actives used in the formulation?

An NDC is not typically required for an API (Active Pharmaceutical Ingredient) used solely as a raw material in the manufacturing of drug products. However, some sunscreen actives in raw material form are listed in the NDC database due to voluntary actions by their suppliers. This practice is common for suppliers who import sunscreen actives into the US to facilitate customs clearance.

USP specification

To ensure compliance, a sunscreen active must be tested against its USP monograph and complies with all specifications. This testing is straightforward for organic sunscreen actives because they are often supplied as pure compounds. You can take a sample, follow the USP test methods, and conduct the tests. However, it is more complicated for inorganic UV filters such as titanium dioxide (TiO₂) and zinc oxide (ZnO).

Most commercial grades of TiO₂ and ZnO used in sunscreen applications have exceedingly small particle sizes and large surface areas. Consequently, they are highly photoactive and can catalyze the oxidation of organic compounds in sunscreen formulations or potentially molecules in the stratum corneum. To mitigate this, especially for TiO₂, surface treatment with inorganic compounds like alumina and/or silica, and organic compounds such as stearic acid or silicones, is common.

As a result, the commercial TiO₂/ZnO powders available to formulators are always a mixture of the active compound and the coating materials. The actives cannot be separated from the coating materials, and the powder, if tested as is, cannot meet USP specifications. USP verification or certification can only be performed by the manufacturer, as they have access to the actives prior to the surface treatment. It is common to see a statement in the Certificate of Analysis (CofA) indicating that the active prior to surface treatment is USP grade, or a separate section in the CofA showing the test results of the active prior to surface treatment.

Due to their large surface area, both attenuation grade TiO₂/ZnO have much moisture absorbed on their surfaces. In the USP specifications for TiO₂, the loss on ignition is set to be less than 13% for the attenuated grade (micronized or nano) TiO₂. However, for ZnO, the specification for loss on ignition is less than 1%. There is no provision for micronized or nano zinc oxide. Therefore, to meet these specifications, the powder needs to be dried before the loss on ignition test.

Zinc Oxide Type

There are three USP monographs related ZnO:

1. Zinc Oxide
2. Zinc Oxide Neutral
3. Zinc Oxide Powder

These monographs specify different purity requirements, with Zinc Oxide having the most stringent criteria. Only USP Zinc Oxide is listed in the FDA sunscreen monograph.¹ While the Zinc Oxide Neutral monograph mentions labeling it for use in sunscreen, its purity level is too low for this purpose. Zinc Oxide Powder also has different, typically lower, purity requirements compared to USP Zinc Oxide. Therefore, it is important to use USP Zinc Oxide for sunscreen formulations to meet FDA standards.

Assaying The Actives

When assaying active ingredients in sunscreen formulations, the method chosen should align with the assay’s purpose. If the goal is to certify compliance of a RM with the United States Pharmacopeia (USP), a USP method must be adopted. However, once an active ingredient is incorporated into a sunscreen formulation or undergoes surface treatment (as is the case with TiO₂ and ZnO), the mixture is no longer considered a USP active. In such cases, the purpose of the assay is to analyze the active ingredient level, not its USP compliance. Therefore, any effective and validated analytical method can be used.

Organic sunscreen actives are often assayed using gas chromatography. The USP method can also be applied to assaying the raw material (RM) as well as the sunscreen composition. For inorganic UV filters, various methods can be used for assaying the treated powder or finished sunscreen products. These methods include X-ray Fluorescence (XRF), titration, Atomic Absorption Spectroscopy (AAS), Ion Chromatography (IC), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

All except the titration method offer high sensitivity and are originally designed for trace metal analysis. Each method has specific pitfalls related to interferences, sample preparation, and operational complexity. It is crucial to fully validate the selected method for each type of sample. Subsequently, managing the analytical workload can be a significant challenge for companies with diverse sunscreen product lines. Each sunscreen formulation may require a specific test protocol and validation to eradicate or minimize the potential matrix effect of different formulations on the test result. Therefore, it is necessary for companies to have a well-organized and efficient analytical testing process to ensure compliance with regulations and maintain product quality across their range of sunscreen products.

Active vs. Non-active TiO₂

The distinction between active and non-active TiO₂ can be particularly confusing in color cosmetics with SPF, where both pigmentary and attenuation-grade TiO₂ are utilized. While assaying and reporting the total TiO₂ content is straightforward, the level can fluctuate among different shades, especially when the range of shades is very wide. This variability makes it challenging to determine the suitable active level for labeling purposes.

To address this issue, there is a practice to report only the level of attenuation-grade TiO₂ content. However, this approach can also be complex, as it requires assaying the intermediate product in the production process. This datapoint is then used in the calculation of the final active content, adding to the intricacy of the process.

Environmental Concern

As we all know, the use of oxybenzone and octinoxate in sunscreens has been banned in Hawaii, Key West in Florida, Palau, the U.S. Virgin Islands, Aruba, Bonaire, and Mexico due to their toxicity towards coral reefs. This has reduced the number of sunscreen actives available for formulation in sunscreen products in the US. As a result, the use of TiO₂ and especially ZnO has dramatically increased.

It is interesting to note that ZnO is considered aqua toxic by the EPA and ECHA. According to DOT regulations, a pictogram indicating this aqua toxicity must be included in the SDS and on the shipping label. Nonetheless, studies have shown that the level of ZnO introduced into seawater from sunscreen use by consumers is extremely low. ²   It is well below the Predicted No Effect Concentration of Zn²⁺ and Most Sensitive Observed Effect Levels. ^3,4 Therefore, the use of zinc oxide as a sunscreen active is considered safe for marine species and ZnO sunscreen can be claimed as reef safe.

On the other hand, TiO₂ is insoluble in water and has no toxicity towards any species. Its safety towards coral reefs was suggested by Corinaldesi in comparison to ZnO. ³ Of course, nano TiO₂ is photo-catalytical under UV exposure if uncoated. However, with proper coating, the photocatalytic activity is suppressed, making TiO₂ environmentally friendly. It could be the best sunscreen active from an environmental perspective.

However, TiO₂ has a higher refractive index and often leaves a white cast on the skin if not formulated properly, which presents a significant challenge to formulators. Despite its environmental advantages, it has not been as widely considered for sunscreen formulations as zinc oxide in recent years.

In conclusion, navigating the regulatory landscape and environmental considerations for sunscreen actives is complex. Manufacturers must balance regulatory compliance, environmental safety, and formulation challenges to develop effective and safe sunscreen products.

References:

1. Federal Register / Vol. 64, No. 98 / Friday, May 21, 1999 /Rules and Regulations: Sunscreen Drug Products For Over–The-Counter Human Use; Final Monograph.
2. Antonio Tovar-Sa´nchezet al., Sunscreen Products as Emerging Pollutants to Coastal Waters, PLOS ONE, June 2013, Volume 8, Issue 6, e65451.
3. C Corinaldesi, Impact of inorganic UV filters contained in sunscreen products on tropical stony corals (Acropora spp.), Sci Total Enviro., 2018 Oct 1:637-638:1279-1285.
4. Ingo B. Miller, Toxic effects of UV filters from sunscreens on coral reef revisited: regulatory aspects for “reef safe” products, Environ Sci Eur (2021) 33:74.
5. Andreas P. Gondikas et al., Release of TiO₂ Nanoparticles from Sunscreens into Surface Waters: A One-Year Survey at the Old Danube Recreational Lake; Sci. Technol.2014, 48, 10, 5415–5422.

ABOUT THE AUTHOR

Dr. Yun Shao joined Kobo Products Inc. in 1996 and currently serves as the Senior Vice President of R&D. With over 20 years of experience, he is a seasoned expert in inorganic sunscreen technology, micro TiO₂ and ZnO development, pigment surface treatment, dispersion technology, specialty cosmetic ingredients, color cosmetics, and global cosmetic ingredient regulations.

Dr. Shao has shared his work at prestigious scientific meetings, including the IFSCC Congress, SCC Annual Scientific Meeting, and FLSCC Sunscreen Symposium. He holds nine patents and has co-authored several book chapters and technical papers on surface treatment and inorganic sunscreen formulations.

Dr. Shao earned his Ph.D. in Polymer Chemistry from Rensselaer Polytechnic Institute and his B.S. in Applied Chemistry from the University of Science and Technology of China. He is a member of the Society of Cosmetic Chemists and a founding member of the Chinese American Cosmetic Professional Association.

Gut Microbial Metabolites of Dietary Polyphenols and Their Skin Health Benefits

Author:
Hang Ma, Ph.D.
Research Unit for Nutraceutical and Cosmeceutical Applications (RUNCA), Biomedical and Pharmaceutical Sciences, College of Pharmacy, The University of Rhode Island

Imagine your gastrointestinal tract as a sophisticated biochemical laboratory, where the vast community of gut microbes metabolizes polyphenols— plant-derived compounds widely found in fruits, vegetables, coffees, and teas. Through complex enzymatic processes, these microbes break down polyphenols into a variety of smaller, bioactive compounds known as polyphenol microbial metabolites (PMMs). These metabolites are important to overall human health: they enhance antioxidant defenses, modulate inflammatory responses, and may even alleviate diseases.

Figure 1. Illustration of gut microbial biotransformation of dietary polyphenols to their metabolites.

A fun fact about PMMs: they can act like a natural “skincare” from within your body!

Here are some common PMMs you can intake from your foods and their potential skin-beneficial effects:

1. Urolithins: They are PMMs derived from ellagitannins and ellagic acid found in various fruits (e.g. pomegranate) and nuts. They have been studied for anti-cancer and neuroprotective effects. For instance, urolithin A (UA) is reported to be safe and can improve mitochondrial and cellular health in humans [1]. In addition, UA can exert anti-aging effects on human skin fibroblasts [2] and protect skin cells from UVA-induced cellular damage [3].
2. Equol: This compound is produced from the isoflavonoid daidzein found in soy and other legumes. It exerts estrogenic activity and has been studied for its potential benefits in alleviating menopausal symptoms and reducing bone loss. A microarray/protein-based study showed that equol and its isomers protect human skin cells by modulating the expression of aging and inflammatory genes [4].
3. Enterolactone and enterodiol: These are PMMs produced from the microbial fermentation of lignans, a group of unique phytochemicals found in flaxseeds, sesame seeds, maple syrup extract, and other plant sources. These metabolites have been linked to potential benefits in reducing the risk of hormone-related cancers [5].
4. Hydroxyphenylvalerolactones: These PMMs are formed from the breakdown of tea flavonoids (known as catechins) and are thought to contribute to the health benefits of tea. Human clinical studies showed that green tea catechin metabolites including hydroxyphenylvalerolactones can be detected in the skin tissue with skin protective effects against UV-induced inflammation [6].
5. Simple phenols: These compounds include tyrosol and hydroxytyrosol, which are PMMs of olive and jasmine phenolics, such as oleuropein. A reported study showed that hydroxytyrosol and its parent compound oleuropein are skin permeable and they can inhibit elastase and collagenase (enzymes that cause skin wrinkles) as well as protect skin cells in a synergistic manner [7].

PMMs hold significant promise for skin health. Partially, this is due to their promising biological effects such as antioxidant properties. PMMs can protect the skin from premature aging by neutralizing harmful free radicals. Additionally, their anti-inflammatory capabilities may soothe irritated skin, reducing redness and swelling associated with conditions like acne, eczema, and psoriasis. Some of these metabolites also exhibit antimicrobial properties that can prevent skin infections by inhibiting the growth of pathogens. Beyond these benefits, phenolic metabolites enhance the skin’s barrier function, improving its natural defenses and moisture retention. Incorporating phenolic-rich foods into one’s diet can support the production of these beneficial metabolites, potentially enhancing skin health from within. For example, a recent randomized double-blind placebo-controlled clinical study showed that a pomegranate supplement (i.e. Pomella^®) can promote skin health and beauty from within properties by improving biomarkers that are associated with visible wrinkles and moisture in a healthy population. Interestingly, polyphenols in pomegranate and their PMMs are thought to exert synergistic influence on both gut and skin microbiomes [8].

Although the potential of PMMs in skincare is promising, several challenges hinder their application and effectiveness. First, the variability in individual gut microbiota composition means that not everyone produces these beneficial metabolites at the same levels. Additionally, the complexity of accurately studying these metabolites in skin tissue remains challenging. These factors add layers to the barrier of developing PMMs-based topical skincare products. Research and development efforts are directed to effectively deliver these compounds to the skin and to ensure the stability and absorption of PMMs. Lastly, regulatory hurdles related to proving the health claims of such products can slow down their introduction to the market.

The future of utilizing PMMs in skincare is an exciting frontier with immense potential. Efforts are needed to advance our understanding of how these compounds interact with the skin’s microbiome and cellular structures, aiming to enhance their bioavailability and stability for effective topical applications. Collaborative research from all angles including microbiology, dermatology, and cosmetic science is crucial to developing new skincare formulations that harness these promising PMMs. Additionally, the industry is expected to innovate with sustainable and scientifically-backed products that leverage the health-promoting potential of PMMs.

References

1. Andreux, Pénélope A., et al. “The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans.” Nature Metabolism 1.6 (2019): 595-603.
2. Liu, Chun-feng, et al. “Antiaging effects of urolithin A on replicative senescent human skin fibroblasts.” Rejuvenation Research 22.3 (2019): 191-200.
3. Liu, Wenjie, et al. “Urolithin A protects human dermal fibroblasts from UVA-induced photoaging through NRF2 activation and mitophagy.” Journal of Photochemistry and Photobiology B: Biology 232 (2022): 112462.
4. Lephart, Edwin D. “Protective effects of equol and their polyphenolic isomers against dermal aging: microarray/protein evidence with clinical implications and unique delivery into human skin.” Pharmaceutical Biology 51.11 (2013): 1393-1400.
5. Adlercreutz, Herman. “Lignans and human health.” Critical reviews in clinical laboratory sciences 44.5-6 (2007): 483-525.
6. Rhodes, Lesley E., et al. “Oral green tea catechin metabolites are incorporated into human skin and protect against UV radiation-induced cutaneous inflammation in association with reduced production of pro-inflammatory eicosanoid 12-hydroxyeicosatetraenoic acid.” British Journal of Nutrition 110.5 (2013): 891-900.
7. Li, Huifang, et al. “Dietary polyphenol oleuropein and its metabolite hydroxytyrosol are moderate skin permeable elastase and collagenase inhibitors with synergistic cellular antioxidant effects in human skin fibroblasts.” International Journal of Food Sciences and Nutrition 73.4 (2022): 460-470.
8. Chakkalakal, Mincy, et al. “Prospective randomized double-blind placebo-controlled study of oral pomegranate extract on skin wrinkles, biophysical features, and the gut-skin axis.” Journal of Clinical Medicine 11.22 (2022): 6724.

The acceleration of climate change driven events is creating an increasing pressure on the environment and living organisms that depend upon it with consequences that will be hard to fix or reverse in the future. Every living organism that is exposed to environmental changes is impacted. We need to understand the scenario to put in place effective actions to mitigate the changes that will affect the environment we know and the way we source natural ingredients for cosmetic use. The call for action is now.

Global Warming
We exist in a thin layer of the atmosphere, 7 miles above sea level. Life has been preserved for thousands of years with the right conditions of temperature and air, mostly nitrogen and oxygen, but also greenhouse gases such as methane, nitrous oxide and carbon dioxide that released in the atmosphere contributed to stabilize the right temperature for living organisms. However, since the industrial revolution in the late 1800s, increasing burning of coal, oil, and natural gas, has caused more carbon dioxide to be released in the atmosphere, eventually trapping the heat, with the consequence of increasing its temperature, a process referred as global warming. Extreme weather has also triggered melting of glaciers, ice caps and contributed to sea level rise. In the US, greenhouse gas emissions linked to global warming, have been associated with transportation, electricity production, industry, residential/commercial heating, and agriculture practices.1

Climate Change and its Effect on Plant Growth
A plant needs water, air, sunlight, optimal temperature, and the right soil to properly grow. Climate change is affecting all the above, except for sunlight.

With most of the water being saltwater from the ocean, only 3% is fresh (glaciers, groundwater, lakes, rivers, etc.). A warmer climate is causing an increased water evaporation, eventually trapped in the atmosphere. Cycles of rain are altered; dry areas are getting drier and wet areas wetter. Plants would find it difficult to adapt to these changes and in dry areas, farmers would need more and more ground water to sustain irrigation.

With carbon dioxide increasing in the atmosphere, plants are growing faster, but weeds also, with the difficulty to control them. Plant-feeding insects are proliferating due to the decrease in plant nutritional value and increase in sugar content when plants are grown under a higher carbon dioxide atmosphere. This decrease in nutritional value is a concern for the human diet but also for other uses (such as cosmetics and supplements and their ingredients quality). Plants contain less protein, zinc, iron, and vitamins, especially B vitamins.2,3

Temperature changes during nighttime or daytime alter the normal growth of the plant and its reproductive stage. With increased heat some plants grow faster, and farmers would need to manage irrigation, planting, harvesting, etc., but extreme heat would harm plants, especially during pollination, and the yield would decrease dramatically. Many plants like winter exposure and warmer winter will also reduce yield or select out many plant varieties. In general, because of increasing heat, the plant cultivation geographical map is shifting, moving northern.

Finally, climate change is also affecting the quality of the soil, so essential for life development. A healthy soil is a living system that sustains plants, animals, and humans.4 It contains billions of bacteria, fungi, nematodes, insects, spiders, and many other organisms interacting together and with the plant’s roots. Soil contains organic matter, often derived from living organisms but also from plant decay (humus). This organic matter is vital for life, it absorbs water optimally. The symbiosis between the soil and the plant’s root is very important, and it helps keep the plant healthy. The quality of the soil translates in the quality of the plant and its products, the massive cleaning of forest for land cultivation is depleting the soil and carbon is released in the atmosphere instead of being kept in the soil.

Some examples of Plants disruption
Many plants providing ingredients for our cosmetic products grow in coastal zones, such as 70% of coconuts trees. These zones are threatened by rising seas. Moreover, scientist studying coconuts plants have shown a negative impact on growth by rising temperatures.5 The cultivation and yield of Lavender, Jasmine, and Rose, in Grasse, France, have been seriously affected recently by more extreme weather, including droughts.6 These plants are essential to produce essential oils for the fragrance industry. Medicinal plants are more and more popular in our industry due to a wellness push. Many species of medicinal plants grow on mountains and many of them are difficult to cultivate. Warmer temperatures are threatening most species, pushing species to adapt and grow to higher altitudes to remain viable with species not able to adapt and possibly to disappear.7 Basic life is changing in the ocean, too. Phytoplankton and Algae are declining due to a warmer ocean and efficiency in photosynthesis is affected.8 With declining fishing and algae availability in the arctic sea due to climate change effect on temperature and on El Nino driving stream, global sourcing of omega-3 has been challenged with main production shifting to indoor algae cultivation and fermentation.9

Conclusions
Climate change is real and we, as an industry, need to work with our suppliers to sustain our ingredients sourcing. Development of climate change resistant species, vertical and cellular farming to balance the pressure on cultivation and wild picking, and finally optimization of plant usage by improved extraction and process methodology, are urgently needed to reduce the demand on classical supply chain and implement a more sustainable use of resources.

References
1. Sources of Greenhouse Gas Emissions. EPA, 2015
2. Samuel S et al. Increasing CO2 threatens human nutrition. Nature 510 (7503):139-42, 2014
3. Chunwu Zhu, et al. Carbon dioxide levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries. Science Advances 4(5); 2, 2018
4. Soil Health. USDA, 2019
5. Sunoy J, et al. Impact of climate change on plantation crops: coconuts. In Impact of Climate Change on Plantation Crops, ed. KB Hebbar et al., 2017
6. Quito A. The top luxury company in the world is fighting to save the flowers that go into its perfume. Quartz, 2019
7. Das M, et al. Impact of climate change on medicinal and aromatic plants: review. Indian J Agric Sci 86: 1375-82, 2016
8. Roxy MK, et al. A reduction in marine primary productivity driven by rapid warming over the tropical Indian ocean. Geophysical Research Letters 43(2): 826, 2016
9. Cheung W, et al. Climate change exacerbates nutrient disparities from seafood. Nature Climate Change 13: 1242-49, 2023

About the Author

Giorgio Dell’Acqua is passionate about the environment and sustainability. He has given many lectures in the past on sustainable supply chain, natural ingredients and upcycling as well as publishing several articles for the industry on this topic (see below for references). Giorgio is currently Chief Science Officer at Nutrafol, a company specialized in natural based supplements and topicals for healthy hair and scalp. After obtaining his PhD in Cell Biology in 1989, Giorgio worked in Academia for 15 years as an investigator in applied medical research. Moving to the private sector in 2000, he has spent the last 20+ years as an executive and cosmetic scientist in the personal care industry. During his career, he directed R&D, Innovation, Science, and Product Development at multiple companies. He has helped bring 200+ successful active ingredients and finished products to market, has authored more than 90 publications in medicine and cosmetic science, and he holds 2 patents. Giorgio is also on the executive board of the US Society of Cosmetic Chemists (SCC) as its 2024 secretary, he is the chair for the NYSCC outreach committee and he is a member of the NYSCC Scientific Committee.

References (sustainability)

Han M, Dell’Acqua G. Exploring extremophiles: a novel and sustainable path for innovation in the cosmetic industry. Cosmetiscope 30(2): 1-7, 2024
Dell’Acqua G. Green isn’t enough. Social Progress is the next chapter for naturals. Cosmet. Toil. (Cover page article), 134(7): 28-40, 2019
Dell’Acqua G. Recycling natural by-products from food and agriculture waste into powerful active ingredients for cosmetic applications. H&PC Today 13(3): 16-19, 2018
Dell’Acqua G. Sustainable product development. CTSCC Nutmeg Newsletter 35(3): 7-11, 2018
Dell’Acqua G. Communities under the forest – Can we separate humans from trees? NYSCC Cosmetiscope, 24(2): 15-16, 2018
Dell’Acqua G. Garbage to glamour: recycling food by-products for skin care. Cosmet. Toil. (Cover page article), 132(2): 28-37, 2017
Dell’Acqua G. The challenges of sustainable development. NYSCC Cosmetiscope 23(2):1-6, 2017
Dell’Acqua G. Sustainable ingredients with scientific edge. Midwest SCC Scoop 47(6):7-11, 2015
Dell’Acqua G, Calloni G. Sustainable ingredients and innovation in cosmetics. Cosmet. Toil., 128(8): 528-536, 2013

Defining beauty is a complex and multifaceted task that can be accomplished both topically and from within. Beauty is one of those feel-good life deliverables that both gives and receives, making it a personalized priority for all of us.

Beauty is a matter of interpretation, appreciation, and commitment. It all starts with a strong dedication and willingness to pursue practices that feed overall wellness persistently. Beauty is intricately linked to health, with factors such as restful sleep, regular exercise, and a balanced diet playing pivotal roles in maintaining radiant skin, bright eyes, and lustrous hair and nails.

As time passes, aging becomes a concern for many people, prompting changes in the way we view our routines, diet, and abilities. The use of topical products is first line defense and a natural progression towards influencing the rate at which you age as it hits on many sensorial notes both on a neural level and through repetitive muscle entrainment, making it easy to create a positive habit toward maintaining your health. The downside is that topical products typically work on or underneath the superficial surface of skin and hair. The epidermis, and the hair cuticle, respectively, are designed by nature to keep things out in an environment that is constantly changing. All of this is a good thing. From a product development perspective, it becomes a never-ending effort to correct and maintain your skin and hair without adding to the everyday stress of imbalance that already exists.

One of the overlooked functions of skin is that it acts as an excretory organ, much of what goes on inside your body has a direct effect on how your skin functions and ultimately looks. Furthermore, being the largest organ, it is privileged with miles of vessels moving nutrients and metabolites of every category to all parts of our skin, hair, and nails. Because of this nutrient flow, many of these nutrients and by-products of their metabolism find their way to the surface of the skin acting in concert with the skin’s topical biochemistry and microbial ecology, influencing immune learning and defense. As all of this occurs, your gut health, mental health, sleep patterns and attitudes are being transmitted through your skin in both acute and long-term ways. Like growth rings on a tree, your skin, hair, and nails, reflect a moment in time and the conditions within that moment.  If beauty is what we seek, I suggest blending all the possibilities there are into the best possible moment in time.

Taking a new perspective on empowering beauty is leveraging the wonders of a comprehensive approach to both topical care and support from within.

Beauty-from-within supplements are becoming more popular amongst consumers. It is one of the fastest-growing categories in the nutraceuticals industry with an above average CAGR.

Internally supporting beauty is a strategy that can address skin and hair at almost every level, leading to lasting results and a more consistent routine resulting in less overall stress.  This integrated approach, focusing on creating a positive feedback loop of promoting overall health and wellness, can lead to healthier, more radiant skin, brighter eyes, and lustrous hair. This exponentially grows the possibilities of intervention in terms of product development and gives the consumer a sense of control over their aging process and creating enduring foundational results with significant benefits over a single armed beauty approach.

Under this approach, beauty is linked to overall wellness, lifestyle, diet, exercise, sleep, and stress management, which become additional targets to support through dietary supplementation and lifestyle changes.

I encourage you to visit the events page on the NYSCC website and register for the “Beauty from Within: Next Level Beauty Care & Wellness Strategies” event being held at the Pleasantdale Chateau in West Orange, NJ on March 26th. There is a great line up of speakers that will explore and inspire all the wonders of beauty from both sides. I look forward to seeing you there.

Author Bio:

Michael Anthonavage serves as the VP of Innovation at Vitaquest International, dedicated to expanding the supplement market footprint and ensuring their customers gain a competitive edge. With expertise in bringing new technologies to market, championing innovation and growth for all areas of health and nutrition as well as many aspects of skin and haircare product development.  Michael is a seasoned skin biologist, research scientist, educator, and a member of the scientific advisory board for the New York Society of Cosmetic Chemists for the past 5 years.

Here’s a hot flash you may not have heard before.  You’re not aging.  You’re rusting. As we get older, we start to face a complexion that looks duller, dingy, cloudier, less luminous. And more unevenly discolored.  The reason?  Iron is the most abundant transition metal in human body and the best-known driving force behind oxygen free radical formation through Fenton and Haber-Weiss reactions (Pierre and Fontecave 1999). Yes, the irony of iron is that iron is the element essential for building strong structures and machines but can also be the cause of their deterioration through rust. Oxidative damage a.k.a. – rusting is due to two distinct but surprisingly related functions: the build-up of iron in the skin as we get older coupled with a slowing of the skin’s natural exfoliation process. These result in iron staying in the skin for 56 days instead of 28 days as skin turnover time (Weintraub et al. 1965).

Here’s another conundrum.  In pre-menopause, excess iron in the body and skin is eliminated two ways: through monthly menstruation and through exfoliation. When menstruation ceases, iron levels can surge. Excess iron in the body is common with the onset of menopause.  In fact, iron can accumulate in the skin and is clinically shown to increase by as much as +42% pre through post menopause (Pelle et al. 2013). This excess iron is normally eliminated through menstruation as well as natural exfoliation.  The cessation of menstruation coupled with the deceleration of exfoliation limits the capacity to remove excess iron from the skin.

When body iron storage increases, skin too is exposed to higher levels of iron, which in turn can cause oxidative damage as the excess iron reacts with UVA. The result: skin aging and photoaging is accelerated. For example, ferritin is the iron storage protein for excess iron with a capacity of binding up to 4,500 atoms of iron per ferritin. It consists of heavy (H) and light (L) chain subunits. It was shown that ferritin can be immediately degraded by UVA doses of 100 and 250 kJ/m², releasing large amounts of iron for Fenton and Haber-Weiss reactions, producing oxygen free radicals (Pourzand et al. 1999). In a cell culture model mimicking menopausal conditions, increased iron and UVA were found to significantly increase an enzyme called collagenase-1 (Jian et al. 2011). Increased activity of collagenase-1 increases collagen degradation, causing wrinkles initially and skin thinning when we get older.

Like rust on metal, higher levels of iron when exposed to UV radiation, blue light, air pollutants and irritants from other sources results in increased oxidative damage in skin.  If you’ve ever seen a rusty bicycle, you know the corrosive damage the environment has on metal.  Oxidative stress begets skin-aging yellowing, dullness, dark spots and discolorations as well as wrinkles, loss of elasticity and other signs of aging.

Until now, antioxidants have been the only defense to attempt to neutralize oxidants after they are formed. Chelation can be used to sequester “free” iron, but it cannot compete to take away from iron in ferritin. The antioxidant and chelation approaches are retroactive and often too late (Table 1). They can only battle the symptoms, but they do not treat the underlying cause.

Table 1. Mode of actions of antioxidants, chelation, and de-ironizing inducer (DII) *

*: The skin is subject to a constant onslaught of free radicals catalyzed by iron-mediated Fenton and Haber-Weiss reactions.

A novel class of actives termed De-ironizing Inducers Technology (DII®) can do what no free-radical neutralizing antioxidant or chelation can do. It reduces iron in ferritin before it is converted to skin-damaging free radicals.  The patented DII® features 3-o-ethyl-ascorbic acid and pearl powder in the right ratios to effectively reduce iron in skin (US Patent 10792240). Research shows that when either alone or when too much of one exists without the other, iron reduction cannot be accomplished.  Ascorbic acid, also known as vitamin C helps release iron deposits from ferritin. Pearl Powder, a soft form of calcium carbonate, absorbs the released iron ions by exchanging them with calcium ions and, thus, removes skin-rusting iron deposits (Figure 1). These two previously incompatible ingredients work in unison to help prevent oxidative stress from forming in the first place, rather than attempting to neutralize free radicals after they appear as most antioxidants do. Without the need to fight free radicals, skin-rejuvenating Hyaluronic Acid plus Tetrapeptide-11 repair previous damage done and the goes one step further to help rebuild collagen, clarity, elasticity and tone / skin’s health and appearance.

Your skin glows with good health. And rust is history!

It is important to note that, while this discovery is made using menopausal model, the DII® is applicable to all ages. Estrogen peaks at age 25 and iron starts to increase from the same age. While estrogen sharply decreases during the menopausal transition period, iron dramatically increases during the same period. DII® may be more age defying in young women but more disrupting with higher success rate in older women. Man starts to accumulate iron from the 20s to the 30s and skin pigmentation is higher in man than in woman (Rahrovan et al. 2018). As a result, DII® is also applicable to man.

References:

Jian J, Pelle E, Yang Q, Pernodet N, Maes D, Huang X. (2011). Iron sensitizes keratinocytes and fibroblasts to uva-mediated matrix metalloproteinase-1 through tnf-alpha and erk activation. Exp Dermatol 20:249-254. https://www.ncbi.nlm.nih.gov/pubmed/20701626

Pelle E, Jian J, Zhang Q, Muizzuddin N, Yang Q, Dai J, et al. (2013). Menopause increases the iron storage protein ferritin in skin. J Cosmet Sci 64:175-179. https://www.ncbi.nlm.nih.gov/pubmed/23752032

Pierre JL, Fontecave M. (1999). Iron and activated oxygen species in biology: The basic chemistry. Biometals 12:195-199. https://www.ncbi.nlm.nih.gov/pubmed/10581682

Pourzand C, Watkin RD, Brown JE, Tyrrell RM. (1999). Ultraviolet a radiation induces immediate release of iron in human primary skin fibroblasts: The role of ferritin. Proc Natl Acad Sci U S A 96:6751-6756. https://www.ncbi.nlm.nih.gov/pubmed/10359784

Rahrovan S, Fanian F, Mehryan P, Humbert P, Firooz A. (2018). Male versus female skin: What dermatologists and cosmeticians should know. Int J Womens Dermatol 4:122-130. https://www.ncbi.nlm.nih.gov/pubmed/30175213

About the Author

Biography: Xi Huang has investigated iron’s role in diseases for more than three decades and is credited in more than 90 peer-reviewed publications, many of which demonstrate that excess iron is an important risk factor in women’s health. Dr. Huang was a faculty member at New York UniversitySchool of Medicine and his research laboratory has shown that iron accumulation due to the cessation of menstruation in postmenopausal women contributes to osteoporosis and skin aging. Dr. Huang is the founder and president of FE:I Beauty Tech, the parent company of i-On Skincare (www.ionskincare.com). Dr. Huang received his Ph.D. and M.S. in Toxicology and Applied Pharmacology from the Université Denis Diderot – Paris VII and received his undergraduate degree from China Agricultural University.

Coloring agents are essential components of certain cosmetic products, especially color cosmetic formulations. Most cosmetic colorants are synthetic and are regulated globally.  In the US, they are regulated by FDA with monographs for each and all located in Title 21 of the Code of Federal regulations, Parts 73 and 74. In the EU, allowed cosmetic colorants are listed in Annex IV, Regulation 1223/2009/EC on Cosmetic Products, as corrected by Corrigendum to Commission Regulation (EU) 2021/850, 17 June 2021. Many colorants on that list are also used in food and have corresponding E (Europe) numbers such as E-171 for TiO₂ and E-172 for iron oxides. In such cases, the specifications for food colorants are used for cosmetic application.  Therefore, it is common to see a note in technical datasheet for a cosmetic colorant stating it complies with the 21CFR and E number (like E-172 for iron oxides) specifications.

Although many of us formulate with colorants frequently, we seem to need help on gaining complete clarity on certain aspects of them. In this blog, we will go over some fundamentals and a few common confusions about certain pigments.  Let’s first start with some terms that we often hear.

Dye:  It is a material that imparts a color and is soluble in the vehicle or substrate in which it is dispersed.

Pigment:  It is a material that is insoluble in the vehicle or substrate in which it is dispersed. True pigments are colorants completely insoluble based on their chemical structure and constituent groups. They typically do not contain the normal substitution groups that promote water solubility, such as sulfonates (-SO₃), carboxylic acid (-COOH) or hydroxyl groups (-OH). Hence, there is no bleeding in hydrous systems. There are only two examples of true pigments used in cosmetics:  D&C Red No. 30 and D&C Red No. 36.

For leave-on cosmetic applications, pigments instead of dyes are often used because dyes are hard to remove after use, thus, stain the skin. Dyes are more commonly used in rinse-off products such as shampoo and mouth rinse. Now let’s go a little further:

Toner:  It is a pigment that is produced by precipitating a water-soluble dye as a metal salt. Typical metals used for this precipitation are sodium, calcium, barium and strontium. e.g., D&C Red 7 Ca Salt. (be aware that it is not a lake)

Lake:  It is a pigment produced by absorbing a water-soluble dye or a primary toner onto an insoluble substrate. All the lakes are pigments.

F, D and C codes in the names of a colorant stands for its approved use in Food, Drug and Cosmetics. A colorant must meet its purities requirements to ensure its safety. FDA separates color additives into two categories:

1. Colorant subject to certification: they are derived primarily from petroleum and are known as coal-tar Most synthetic, organic colorants fall in this category. They must be batch certified by the FDA. They are further divided into two categories:
2. Certifiable Primary Colors: They are pure color which contain no extenders or diluents. They have color names and numbers assigned such as FD&C Yellow 5, D&C Red 6 and Ext. D&C Violet 2.
3. Certifiable Color Lakes: Lakes follow the same restrictions as the primary colors with the additional rule that they must have the name of the precipitating metal and the word “lake”. An example would be FD&C Yellow 5 Al Lake.
4. Colorant exempt from certification: These are natural organic colorants and synthetic inorganics obtained largely from mineral, plant, or animal sources. Although batch certification is not required, purity must be tested by the manufacturer to meet FDA specifications. Examples are Titanium dioxide and Iron oxides.

Now that we have gone over the general terms and regulatory aspects of colorants, let’s look at common ambiguities about a few specific pigments:

1. Rutile and anatase

First, they both are TiO₂, but refer to two crystalline structures. It is like using Coke or Pepsi to represent carbonated soft drinks. Anatase is slightly softer and less abrasive than rutile. This makes little difference to the skin feel but can make a big difference in TiO₂ production process.  Rutile is so abrasive that it can wear out the equipment that processes hundred to thousands of tons per campaign. Consequently, rutile is often surface treated with alumina to extend the useful life of the equipment in addition to provide other benefits.

Rutile has a slightly higher refractive index than anatase, and thus, it can scatter light more effectively. So, does it mean that Rutile is more opaque? Not quite. Opacity is the result of scattering which depends as much on the size and size distribution of the pigment particles as on its refractive index. In reality, it is rare to find a rutile and an anatase that have the same particle size, let alone size distribution. Therefore, being rutile or anatase does not necessarily indicate a higher or lower opacity.

Commercial anatase is usually made to have a small primary particle size, in a range of about 140 – 170 nm. That of rutile is often bigger, roughly 170 – 250 nm.  Due to its smaller size, anatase scatters blue light slightly more, and thus, imparts a blueish undertone.  This is the reason that anatase is often said to be bluer than rutile.

Lastly, the production processes, chloride and sulphate, are often brought into discussion about TiO₂.  In Chloride process, TiCl₄ is vaporized and burnt into rutile.  In sulphate process, Ti(SO₄)₂ is neutralized with base to generate anatase. If aluminum salt is used as the inducer, rutile TiO₂ can also be made via the sulphate process. TiO₂ made from a Chloride process often has a lower level of contaminants, which translates into high purity and clean color. This had been indeed the case in the past, but not so much anymore since the sulphate process technology has been greatly improved over the years.

1. Carbon black

 Carbon black can be made via several processes. In the US, carbon black as a cosmetic color additive is called D&C Black No. 2, a high-purity carbon black prepared by the oil furnace process.¹ It is manufactured by the combustion of aromatic petroleum oil feedstock and consists essentially of pure carbon, formed as aggregated fine particles with a surface area range of 200 to 260 m²/g.

JSCI monograph requires Carbon black to be obtained by incomplete combustion of natural gas or liquid hydrocarbon. Such carbon black is often called channel black and is not approved by the FDA.  This, unfortunately, adds unnecessary complexity to formulating for the global market.

2. Chromium oxide and Chromium hydroxide green

Hexavalent Chromium (Cr⁶⁺) is known to be carcinogenic, thus, it should not be present or at a very low level in cosmetics products. However, its presence is unavoidable due to the chemistry and manufacturing process. For both pigments, the FDA set a limit of 2% NaOH extract, not more than 0.1% as Cr₂O₃ (based on sample weight). ² This limit is equivalent to 684 or 513 ppm maximum Hexavalent Chromium, respectively. The actual level of Cr⁶⁺ in a commercial grade needs to be tested for calculating the final level in a finished formulation.

3. Mica and Pearlescent pigments

A common restriction people often talk about is the size limit of 150 mm. Mica is an approved colorant for drug use, and the FDA has imposed a size limit on it.  Mica can also be used as a colorant for cosmetic applications for which the FDA does not list any size limit in the monograph. Moreover, mica can be used in cosmetics as filler, a category that the FDA does not regulate with specific requirements.

Efforts have been made to list Mica-based pearlescent pigments as approved colorants for cosmetic purposes, but this has not happened yet. as of now, such pigments have been approved as colorants only for drug use, and the corresponding specifications require that the mica meets the colorant specifications for drug use.  This is likely the reason that we hear the 150-mm size limit in our industry.  As mentioned above, mica-based pigments are not approved colorants for cosmetic use. Consequently, the composition has to be expressed as a mixture of individual components such as, for instance, mica and titanium dioxide. Each of these ingredients needs to meet the corresponding FDA specification if applicable.  The size limit on mica for drug use may not be observed.

4. Zinc oxide

Zinc oxide is a long approved cosmetic colorant, though its use as opacificer in cosmetics is limited. That main reason is that its opacity is much lower than TiO₂ due to its lower refractive index (2 vs. 2.7).  Roughly 3 times more ZnO is needed to achieve the same degree of opacity of TiO₂. Moreover, ZnO is slightly soluble in water, resulting in the pH of formulations containing ZnO to be above 7.5.

As of August 7, 2022, the use of TiO₂ as food colorant has been banned in the EU, directly affecting its use in lip and oral products. Respirable TiO₂ is considered carcinogenic, according to Proposition 65 of the state of California, affecting the use of TiO₂ in some powder and spray formulations. TiO₂ is difficult to replace because of its unique performance and inertness. In light of the regulatory restriction, ZnO with the right size and high opacity has gained attention recently, especially for anhydrous formulations.

5. Red 6 lake and red 7 lake in Japan

Most FDA approved colorants can be used in Japan. Red 6 lake, widely used in lip products, is a notable exception. The reason is that Red 6 lake is Red 6 Barium salt laked on barium sulfate, but Red 6 Barium salt is not an approved colorant in Japan. On the other hand, Red 7 lake is Red 6 Calcium salt laked on barium sulfate but Red 6 Calcium salt is approved in Japan.  In the case that the shade cannot be achieved without Red 6, Red 6 sodium salt can be used. However, it must be noted that red 6 sodium salt is water soluble, which is opposite to Red 6 lake.

Currently, the FDA has approved 64 color additives for cosmetic use, each of which has its merits and drawbacks due to their unique chemistry and production process.³ The knowledge is important not only for formulating the right color shade, but also for troubleshooting instability and especially, regulatory compliance. The author hopes that this blog will contribute to your learning of cosmetic colorants.

References:

1. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-A/part-74/subpart-C/section-74.2052
2. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-A/part-73/subpart-C/section-73.2327
3. https://www.fda.gov/industry/color-additive-inventories/summary-color-additives-use-united-states-foods-drugs-cosmetics-and-medical-devices#table3A

Introduction

For years, hair care products have been focused on addressing damage by providing solutions to repair, prevent and maintain hair health. With increased awareness, consumers now recognize that healthy scalp is also a fundamental foundation for healthy hair. Holistic care means to restore the hair at its core while maintaining a healthy scalp. With personalization and self-care at the forefront, consumers are looking for solutions that are inspired from skin care with an emphasis on natural and clean ingredients. In this article, we will discuss factors that affect scalp and hair health and provide an overview of the innovative technologies including specialized product treatments that help restore hair and scalp equilibrium.

Stressors that impact hair and scalp equilibrium

Hair and scalp are affected by several factors such as UV exposure, pollution, humidity, mechanical, chemical, physical stressors, and occlusion such as hats and head protectors (like wigs, protective styles etc.) [1]. Sebum on the scalp diffuses along the hair shaft and can attract product build-up and dust from air which can affect the scalp’s overall health. Additionally, the bacterial and yeast proliferation on the scalp is commonly associated with enhanced desquamation, itching, scratching and redness [1]. Some hair products may leave deposits on the scalp, while others can strip hair’s natural oils to the point that it begins to over-produce sebum [2].

Oxidative stress, i.e., free radicals from sources like UV and pollution, can weaken scalp skin health and cause aging [3]. Sensitive scalp syndrome has been reported to arise from increasing levels of air pollution. Symptoms of sensitive scalp include itching, prickling in the scalp, dandruff, oily scalp, and pain in the hair roots. Pollutants also can migrate into the dermis and through the hair follicle (HF), leading to oxidative stress and hair fall [3]. Hormonal changes, medical conditions, heredity, and aging are cited as common causes of hair fall, but there has been a lot of searches for hair loss associated after COVID-19 (+250%) and how to stop hair fall post COVID increased by a whopping 1,250% [4].

The skin surface and follicular openings are recognized sites of rich microbial colonization and intense immune citation, with crosstalk across the skin barrier [5]. A disrupted microbiome may cause infections and inflammation to the scalp [6]. This disruption may aggravate scalp disorders that can lead to acne, eczema, alopecia, scalp psoriasis, seborrheic dermatitis/dandruff, etc. The aforementioned diseases of the skin and the hair follicles [HFs] are all due to the dysfunction of dysbiosis – the imbalance of the skin microbiome [5]. Scalp conditions also impact the quality of hair causing the resultant cuticular cells to be less flexible than normal, which may impair both anchorage and subsequent fiber surface integrity due to an oxidative stress environment [7]. Hair fibers become more brittle and chip off. This results in a rougher cuticle that is also less functionally effective [7].

Cleansing of hair and scalp is also vital. How often you should cleanse your hair is determined based on your overall scalp health and can be attributed to hair texture. Some cleansers can be harsh and overly stripping, removing all natural oils, which disturbs the bacterial environment and can lead to irritation, redness, and flaking [8], while others may have a high oil load that can have a detrimental effect on oily scalp.

As scalp and hair go hand-in-hand, there is also tremendous focus on the damage hair sustains from the environment, washing, bleaching, coloring, and the use of different styling regiments. Hair damage affects all types of cross-linking bonds, including disulfide bonds, and can negatively affect the overall structure and ordering of hair lipids and CMC lipids [9]. Bleaching and coloring leads to dry, brittle-feeling hair and fiber breakage. Repeated washing results in lifted cuticles, while heat damage from drying, straightening, or curling leads to a loss of moisture, frizzy hair, and split ends [10].

Market drivers and trends

Over the past five years, scalp-focused searches have increased by 270% which is tied to the fact that one in two people suffer from a scalp issue [11]. Reportlinker projects the global hair and scalp care market will reach $121.4 billion by 2027 and will grow at an estimated 6.5% CAGR over the next five years [12]. Based on the latest data, Spate recommends that brands offer hair and scalp solutions that support skin barrier repair, moisturization and conditioning of damaged locks [12]. There has also been a rise in complex hair and scalp routines among millennials [4]. Need for different scalp products has increased globally, which aligns with consumers’ desire for benefits that address their individual scalp and hair needs. Consumers are also demanding transparency from brands and want to learn more about the ingredients used in their products and their mechanism of action. They also place a growing emphasis on the use of natural, organic, and clean alternative ingredients.

Advances in technology targeting hair and scalp concerns.

There have been many advancements in technology that provide holistic solutions to help protect, prevent, and restore hair and scalp equilibrium.

Sebum Control:

An ingredient that leverages a novel encapsulation technology*, ensures targeted delivery and controlled release of actives onto the scalp and hair to deliver instant sebum reduction [12]. This ingredient allows consumers to leave more time between washes, leading to water conservation [12]. A naturally occurring amino acid (INCI: Glycerin (and) Water (and) Sarcosine) effectively aids in the reduction of an oily scalp. It helps to reduce flakes on the scalp and assists in rebalancing the microbiome. Additionally, this ingredient also helps fight against stress, pollution, and product build-up [2]. Another ingredient, based on lamellar body-inspired delivery system (INCI: Aqua, Lecithin, Niacinamide, Lysolecithin, Phenethyl Alcohol, Caprylhydroxamic Acid, Tocopheryl Acetate, Caprylyl Glycol, Phytic Acid), has been designed to target hair follicles where it delivers actives to regulate sebum and the microbiome [6].

Oxidative Stress:

Antioxidants are very well known and can be added to any kind of hair product due to their water-based molecular structure. They help to prevent the formation of oxidative stress and provide a wide range of benefits to both hair and scalp. A blend of three natural and powerful antioxidants, an extract of a medicinal plant forms a non-occlusive shield against urban pollution and protects hair and scalp against environmental stress [13]. A fermented extract of organically grown yerba mate leaves (INCI: water (aqua) (and) glycerin (and) Ilex paraguariensis leaf extract) is designed to help protect hair from oxidative stress-induced damage and help maintain healthy hair roots for optimal growth after only one shampoo treatment [12]. Brands like Keep It Anchored (P&G owned) are developing formulas that are powered by a combination of antioxidant salts that relieve oxidative stress, a zinc compound to improve scalp condition and B vitamins known for skin barrier health [8].

* INCI: Aqua (and) Cetyl Palmitate (and) Cucurbita pepo seed extract (and) Disodium EDTA (and) Ethylhexylglycerin (and) Helianthus annuus seed oil (and) Lauryl Glucoside (and) Melaleuca alternifolia leaf oil (and) Phenoxyethanol (and) Rosmarinus officinalis leaf extract (and) Sorbitan Stearate (and) Tocopheryl Acetate

Dandruff:

With zinc pyrithiones (ZPT’s) ban in Europe in cosmetic applications, formulators are now scouting for new active ingredients. A biomarine ingredient derived via biotechnology (INCI: Water (aqua) (and) Pseudoalteromonas Ferment Extract (and) Sodium Salicylate) has been shown to reduce sebum, itchiness, and flakes on the scalp, while also preventing their recurrence in both rinse-off and leave-on applications [4]. An algae oil (INCI: Triolein), containing more than 90% of the beneficial omega-9 helps hydrate, rejuvenate, and repair the scalp. It also nourishes hair follicles and protects against hair fiber lipid degradation upon UV exposure [4]. In addition, another ingredient positioned as an emollient with antimicrobial properties (INCI: decylene glycol), helps protect the skin from scalp to toe. Among other functions, this ingredient supports dandruff control concepts. It also provides a China-compliant alternative to the antidandruff active zinc pyrithione [12].

Hair Loss:

Broccoli and pumpkin seed seem like unexpected choices for formulators developing anti-hair loss products. Sulforaphane, which is an isothiocyanate isolated from broccoli, increased the expression of an enzyme in the liver that accelerated DHT degradation and consequently inhibited hair loss, as shown in an animal model [14]. Clinical efficacy of pumpkin seed oil (PSO) versus 5% minoxidil foam in subjects with female pattern hair loss (FPHL)after three months of treatment showed the pumpkin oil significantly decreased hair shaft diversity and the number of vellus hairs with results comparable to the minoxidil foam [14]. Another ingredient, a protein and peptide combination (INCI: Keratin (and) Hydrolyzed Keratin (and) Oxidized Keratin (and) Water) stimulates skin cells to proliferate by up to 160% faster than a placebo while simultaneously stimulating human keratinocyte migration and the expression of collagens IV and VII, thus improving the anchoring of follicles. The ingredient’s anti-inflammatory agent reduced the PGE2 response in cells undergoing inflammatory stress by up to 70%, reducing scalp inflammation, itching and premature hair follicle death [15].

Balancing the Biome:

Inhibition of the growth of harmful bacteria can lead to a better balance in oil secretion; this can be achieved using a unique probiotic fermentation technology rich in amino acids, polysaccharides, protein, and other biologically active substances [16]. A natural prebiotic (INCI: Inulin) can also help rebalance the skin’s microbiota and offer skin hydration that outperforms hyaluronic acid. The prebiotic is based on inulin extracted from chicory root and agave and works by selectively supporting protective organisms to help restore the microbiota layer [6]. Since 2020, We have witnessed a burgeoning of scalp products with Cannabidiol (CBD) boasting microbiome benefits [5] and recently we also have seen use of Cannabigerol (CBG) that helps to rebalance the scalp microbiome and promotes hair growth. Lastly, an ingredient (INCI: Lactobacillus Ferment Lysate) that utilizes the properties of prebiotic oligosaccharides as an approach to postbiotic bacteriocin procurement can deliver scalp moisturization and redness reduction [4].

Protecting hair, beyond the scalp,

Hair, after it rises from the scalp surface, also goes through damage from consumers’ grooming practices and external stimuli. Cleansing, conditioning, and strengthening solutions have been extensively discussed in the past. Currently, the use of bond builders is trending and growing in hair care. They are promoted as being able to penetrate into the hair to improve or restore the internal structure, giving rise to an improvement in mechanical properties [9]. According to this definition, bond builders include a broad range of actives, including organic acids, proteins, and lipids [9]. Brands are employing patented peptide technologies and amino acid complexes in multiple product formats that can help prevent and protect hair from the inside-out against all forms of damage.

What’s new and what’s next.

Ingestible hair care products, such as Nutrafol are gaining popularity for promoting hair and scalp health which has helped fuel further ingredient innovation. The introduction of Keranat in food supplements for hair (soft gels, capsules, beauty drinks/shots and cosmetics is said to offer a natural, vegan solution to effectively fight against hair loss while restoring beauty and brightness [12]. The design of neurocosmetic ingredients that modulate neuronal response to improve scalp care and hair quality could be a promising approach for the development of new hair and scalp care routines [17].

Finally, brands like L’Oréal are fostering partnerships with health tech companies to better understand the biological, clinical, and environmental factors that contribute to skin and hair health over time. This comprehensive understanding contributes to the development of a more precise and inclusive skincare approach that cater to the diverse needs of individuals worldwide [18].

Conclusion

The beauty and personal care industry has made great advancements in understanding the role of microbiome that impacts scalp and hair health. New research and findings help steer brands and ingredient suppliers to develop natural, organic, and sustainable solutions that will be a key focus area for future innovation. Furthermore, ingredients inspired by skin care, traditional ingredients, and biotech will continue to drive the growth of the hair and scalp care category.  It is imperative that brands continue their efforts in developing inclusive and personalized solutions to address consumers specific scalp and hair care needs. Finally, educating consumers on choosing the right products and regime that address their specific needs is crucial, in addition to providing guidance on how to use the products effectively to achieve the desired benefit.

References

1. Luigi Rigano, Ph.D., Rigano Laboratories S.r.l., Milan, Italy, “Hair and Scalp Care Go Hand-in-Hand,” Global Cosmetic Industry, 2016
2. BASF Corporation, “Rebalance the scalp microbiome with Scalposine,” Cosmetics & Toiletries (March 2020)
3. D. Roddick-Lanzilotta, Ph.D., R.J. Kelly, Ph.D., and P.R. Sapsford, “Keratin Blend Anchors Follicles and Prevents Pollution-induced Hair Fall,” Cosmetics & Toiletries (September 2019)
4. Ashlee Cannady, Aprinnova Juliana Gomiero, Stephanie Neplaz, Raphaelle Tron, “Hair and Scalp Cleansing and Care Skinification, ZPT Ban, Fermentation and Damage Repair Self-care,” Cosmetics & Toiletries (June 2022)
5. Sharleen Surin-Lord, Dermatologist, “The ‘Skinification’ of Hair Care” Happi (June 2021)
6. Laura Lam-Phaure, “Formulating on Trend: Skinification of Hair,” Cosmetics & Toiletries (June 2022)
7. “Effect of Scalp Health on Hair Growth,” MedEsthetics (December,2021)
8. Christine Esposito, “Natural Ingredients in Shampoos & Conditioners Benefit Scalp & Hair” Happi (December ,2021)
9. Paul Cornwell, Ph.D., TRI Princeton, Princeton, NJ; and Jennifer Marsh, Ph.D., Procter & Gamble, “How Bond Builders ‘Repair’ Hair,” Cosmetics & Toiletries (February 2023)
10. Rachel Grabenhofer, “Patent Pick: Binding Agreement for Hair Repair,” Global Cosmetic Industry (October 2019)
11. Julia Wray, “Why applicators are the secret ingredients for scalp care,” Cosmetic Business (April 2023)
12. Lisa Doyle, “Hair & Scalp Care: Targeted and Premiumized,” Global Cosmetic Industry (September 2022)
13. Rahn Ag, “Radicare®-Eco: The Urban Antidote for Hair and Scalp,” Cosmetics & Toiletries (April 2022)
14. Mohamed l. Elsaie, Lee Reuveni, Stephanie Neplaz, Sebastien Massard, “Restoring and Reviving Hair: Scalp Health, Laser Treatments, Natural/Sustainable and Deep Repair,” Cosmetics & Toiletries (February 2022)
15. Michele Behrens, “FK Scalp from Keraplast Prevents Hair and Scalp Health Pollution,” Cosmetics & Toiletries (February 2020)
16. Peter Smedley, “Bloomage Highlights Hair Shield, Scalp Care and Fermented Anti-aging at SCC76”, Cosmetics & Toiletries (December 2022)
17. Maria Jose Lopez-Gonzalez, Nuria García and Isabel Devesa, AntalGenics S.L., Elche, Spain, “Neuro-cosmetic Targets for Scalp and Hair Care,” Cosmetics & Toiletries (June 2022)
18. Julia Wray, “L’Oréal embarks on world’s ‘largest and most diverse’ skin and hair study”, Cosmetic Business (July 2023)

The Use of Natural Oils to Treat the Skin

Roger L. McMullen

Fairleigh Dickinson University and Ashland Inc.

The term natural oil refers to a fixed (nonvolatile) oil of animal or plant origin. These types of oils—in contrast to essential (volatile) oils, which are obtained by steam distillation methods of plant matter—are typically obtained from plant seeds and nuts by a mechanical pressing technique or solvent extraction. Natural oils have been used to treat the skin for millennia. For example, evidence suggests that the ancient Egyptians used almond (Prunus amygdalus), balanos (Balanos aegyptiaca), castor (Ricinus communis), moringa (Moringa oleifera), olive (Olea europea), and sesame oil (Sesamum indicum) in cosmetic preparations (1). The natural movement in cosmetics of the twenty first century has led to renewed interest in formulating skin care products with botanical ingredients. In this article, I highlight the use of natural oils in skin care and their benefits for skin health.

Benefits of Natural Oil Treatment

Natural oils nourish, smoothen, sooth, and clean the skin. Skin nourishment is provided by biologically active ingredients in natural oils such as antioxidants and essential fatty acids (2). As an example, the antioxidant activity and health benefits of grape seed oil (Vitis vinifera) mostly stems from the presence of tocopherol, linolenic acid, resveratrol, quercetin, procyanidins, carotenoids, and phytosterols in the oil (3). Essential fatty acids, obtained through the diet or applied topically, are important for maintaining skin health (essential fatty acid deficiently leads to dermatitis) and preventing trans-epidermal water loss (4, 5).

Dry skin is typically rough due to ineffective desquamation. Plant oils can smoothen the surface of skin by providing a lubrication effect and by helping the skin maintain a healthy level of hydration through fortification of the skin barrier. Natural oils can also have a soothing effect on the skin. Anti-inflammatory compounds in the oils can help to reduce skin redness and irritation. Studies have shown that olive, sunflower seed (Helianthus annuus), coconut (Cocos nucifera), safflower seed (Carthamus tinctorius), argan (Argania spinosa), soybean (Glycine max), sesame, jojoba (Simmondsia chinensis), and oat (Avena sativa) oil provide an anti-inflammatory effect in skin (6).

Natural oil-based cleaners are used to remove sebum and makeup from the skin. While conventional surfactants can be very efficacious at cleaning the skin, they can also disrupt the barrier function of skin and remove lipid components important for barrier integrity. A good example of a natural oil-based cleaner was provided by researchers at Mae Fah Luang University in Thailand who demonstrated the effectiveness of tea seed oil (Camellia sinensis) at removing foundation and eyeliner (7).

Composition of Natural Oils

The chief components of natural oils are triglycerides. They usually represent greater than 95% of the composition of natural oils. Triglycerides are formed by the esterification of free fatty acids to glycerol resulting in a molecule with a polar headgroup and three hydrophobic tails (see Figure 1). Triglycerides are synthesized by animals and plants as energy reserves and contain various proportions of saturated, polyunsaturated, and monounsaturated fatty acids. In animals, the fatty acid constituents of triglycerides have greater levels of saturated fats (relative to polyunsaturated and monounsaturated fats), whereas in plants there are greater amounts of polyunsaturated and monounsaturated fats. For this reason, most plant oils are in the liquid state at room temperature.

Figure 1: Molecular structure of a triglyceride. In this example, that fatty acid moieties of the triglyceride contain three distinct entities. The three fatty acid chains in triglycerides can be the same or they can be a mixture. Starting from top to bottom, this triglyceride is composed of palmitic acid (16:0), oleic acid (18:1), and alpha-linolenic acid (18:3).

The fatty acid components of triglycerides can vary in chain length—they can be short (≤ 6 carbons), medium (≤ 12 carbons), or long (12 – 22 carbons)—which effects their physicochemical behavior. In some cases, triglycerides may contain omega-3, omega-6, and omega-9 essential fatty acids. The overall composition of the triglycerides (the types of fatty acids, their length, and the degree of saturation/unsaturation) is unique for each natural oil. For example, coconut oil has higher levels of saturated fats than most plant oils, which is why it exists in the solid state at room temperature.

Natural Oils in Wound Healing

Wound healing consists of the regeneration and tissue repair processes after the development of a chronic (pathological condition) or acute (trauma) lesion in the skin. There are three principal stages in wound healing, which include the inflammatory, proliferative, and remodeling stage. Essentially, these stages are characterized by a series of biochemical and cellular events that involve cytokines, growth factors, and other important bioactive molecules that eventually lead to fibroblast proliferation, collagen synthesis, and epithelialization.

In recent years, it has been established that bioactive fatty acids play an important role in the inflammatory stage of wound healing (8, 9). Essential polyunsaturated fatty acids and their metabolic products are believed to play an integral role in modulating wound healing. Omega-3 (e.g., alpha-linolenic acid) and omega-6 (e.g., linoleic acid) fatty acids metabolize to a number of different molecules including leukotrienes, lipoxins, prostaglandins, and thromboxanes—twenty-carbon chain length bioactive compounds known as eicosanoids (10). In addition to alpha-linolenic acid and linoleic acid, omega-9 fatty acids (oleic acid and erucic acid) were also reported to provide positive anti-inflammatory effects during wound healing (11). In summary, anti-inflammatory and wound healing properties have been demonstrated for various botanical oils including olive oil, grape seed oil, coconut oil, argan oil, jojoba oil, and numerous other oils (6, 12-15).

Natural Oils and Diseases of the Skin

A brief survey of the scientific literature reveals a number of studies investigating the effects of oils on various diseases encountered in dermatology (16). In addition to fatty acids and other lipids in the oils, there are numerous biologically important molecules such as monoterpenes, sesquiterpenes, diterpines (e.g., cannabinoids, tocopherols), triterpenoids (e.g., squalene, sterols), carotenoids, and polyphenols (17). These phytochemicals have been shown to efficaciously alleviate the symptoms of inflammatory skin diseases, such as contact dermatitis, atopic dermatitis, and psoriasis. In addition, dietary supplementation with essential fatty acids has shown beneficial effects in the treatment of acne, atopic dermatitis, pruritis, psoriasis, and skin ulcers (18-20).  Furthermore, supplementation with an omega-3 fatty acid was shown to reduce the risk of skin cancer in organ transplant recipients (patients who undergo transplant procedures have a very high risk of developing skin cancer) (21). There has also been considerable interest in utilizing natural oils produced by the plant Cannabis sativa for the treatment of skin inflammatory diseases. Hemp seed and cannabidiol (CBD) oil have been found to be the most efficacious oils from Cannabis sativa for treating skin inflammatory conditions (22).

Therapeutic Benefits of Natural Oils

One of the principal benefits of treating skin with natural oils is to alleviate dry skin by enhancing its barrier function. Due to compositional differences, each natural oil interacts uniquely with the skin. Some of the most commonly used oils for skin therapy are almond, argan, coconut, evening primrose (Oenothera biennis), jojoba, oat, and olive oil (23, 24). It is noteworthy that while olive oil has a number of reported benefits for skin—mostly for treatment of skin aging, pruritis, and xerosis—there are concerns that it negatively affects skin barrier function (25). Regardless, natural oils help form a physical barrier on the skin surface and function as a source of lipids to fortify the skin’s barrier. Future research could help identify specific oils that should be used for a particular skin treatment modality (26).

Aroma massage therapy consists of the use of essential oils in conjunction with massage techniques. Natural oils are used as carrier oils for the essential oils. In addition to diluting the essential oil, the carrier oil lubricates the skin surface facilitating the massage procedure. Some common carrier oils are almond, coconut, grapeseed, jojoba, and sunflower oil. In general, carrier oils should have a pleasant scent and be aesthetically pleasing when applied to the skin. When choosing a carrier oil, it is best to find an oil that is absorbed well by the skin that does not result in an oleaginous (greasy) sensation.

Neonatal Skin Care

Newborn infants are especially prone to developing dry skin conditions as their skin adapts to life outside of the uterus. From a physiological perspective, infant skin is quite different from adult skin. In infant skin the stratum corneum and epidermis are thinner and there is significant risk of trans-epidermal water loss due to less barrier lipids and natural moisturizing factor. In addition, there is an accelerated breakdown of corneodesmosomes due to the higher surface pH (which affects desquamation) (27). Several studies highlight the possible benefits of treating neonatal skin with botanical oils, such as sunflower, coconut, almond, olive, palm (Elaeis guineensis), and mustard oil (Brassica juncea); however, there seems to be a consensus that further study is warranted to determine efficacy and any proposed mechanisms (28-30). For example, researchers at the University of Sheffield in the UK found that treatment of neonatal skin with olive oil compromised skin barrier integrity and induced mild erythema in patients (31). Furthermore, researchers at Columbia University in New York City reported that olive oil can exacerbate atopic dermatitis and xerosis in pediatric subjects (32).

The Paradoxical Behavior of Natural Oils in Relation to Epidermal Barrier Function

The stratum corneum of skin contains corneocyte cells embedded in a matrix of endogenous lipids consisting of long-chain ceramides, cholesterol, and free fatty acids, organized into multilamellar structures. Sebum is found on the surface of the skin and contains a mixture of triglycerides, wax esters, free fatty acids, squalene, and cholesterol esters. One would expect that treatment of skin with natural oils could help maintain the moisture levels of skin by enhancing its epidermal barrier function via the formation of an occlusive lipid layer on the surface thereby preventing trans-epidermal water loss. However, in recent years it has been discovered that some natural oils may disrupt the skin’s structural lipids thereby compromising stratum corneum barrier function.

Treatment with some oils can fluidize stratum corneum lipids and compromise epidermal barrier function. In fact, natural oils have been used as penetration enhancers in the transdermal delivery of active pharmaceutical ingredients (33, 34). More than likely, the triglycerides in oils that are applied to the skin will be hydrolyzed by resident lipases resulting in the formation of free fatty acids, which can disrupt the ordered structure of lipid lamellae in the stratum corneum (35). In general, the paradoxical effect produced by some oils is thought to be more prevalent in patients suffering from atopic dermatitis and other skin conditions.

Concluding Remarks

Natural lipids are employed in several applications in skin care. In this article, we introduce some of the traditional treatment modalities and highlight some of the most recent studies published in the scientific literature which find health benefits to the skin. The available data suggest an important role for natural oils in treating skin inflammatory disorders, wound healing, skin therapy, and neonatal skin care. Despite the widespread use of natural oils in cosmetic formulations, there is considerable need to conduct further research in this area to better elucidate the mechanisms responsible for the efficacious nature of the oils. Looking ahead to the future, such action will require us to proactively investigate the bioactivity of the components of a broad range of natural oils in a systematic manner. In addition, a better understanding of the detrimental effects of certain oils to epidermal barrier function in specific types of skin needs to be elucidated in future studies.

Acknowledgements

The author expresses his sincere gratitude to Drs. Gopinathan Menon and David J. Moore for revising the text and offering useful suggestions.

References

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9. Lania B, Morari J, Almeida A, Silva M, Vieira-Damiani G, Lins K, et al. Topical essential fatty acid oil on wounds: local and systemic effects. PLoS One. 2019;14(1):e0210059.
10. Jara C, Mendes N, Prado T, de Araújo E. Bioactive fatty acids in the resolution of chronic inflammation in skin wounds. Adv Wound Care (New Rochelle). 2020;9(8):472-90.
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12. Chen C, Nien C, Chen L, Huang K, Chang W, Huang H. Effects of Sapindus mukorossi seed oil on skin wound healing: in vivo and in vitro testing. Int J Mol Sci. 2019;20(10):2579.
13. Nevin K, Rajamohan T. Effect of topical application of virgin coconut oil on skin components and antioxidant status during dermal wound healing in young rats. Skin Pharmacol Physiol. 2010;23(6):290-7.
14. Shivananda Nayak B, Dan Ramdath D, Marshall J, Isitor G, Xue S, Shi J. Wound-healing properties of the oils of Vitis vinifera and Vaccinium macrocarpon. Phytother Res. 2011;25(8):1201-8.
15. Poljšak N, Kreft S, Kočevar Glavač N. Vegetable butters and oils in skin wound healing: scientific evidence for new opportunities in dermatology. Phytother Res. 2020;34(2):254-69.
16. Tabassum N, Hamdani M. Plants used to treat skin diseases. Pharmacogn Rev. 2014;8(15):52-60.
17. Styrczewska M, Zuk M, Boba A, Zalewski I, Kulma A. Use of natural components derived from oil seed plants for treatment of inflammatory skin diseases. Curr Pharm Des. 2019;25(20):2241-63.
18. Thomsen B, Chow E, Sapijaszko M. The potential uses of omega-3 fatty acids in dermatology: a review. J Cutan Med Surg. 2020;24(5):481-94.
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The topic of “biodegradability” has become extremely important over recent years, but still may not be fully understood. The following is a basic overview for formulators and anyone wishing to know more about this critical issue. (Note that regulations, definitions, and practical guidelines on biodegradability are continually changing, and the comments in this blog are intended to offer general insights, not legal definitions or advice.)

Simply put, biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi[1], and once broken down, the byproducts are carbon dioxide and water vapor. “Bio” is the key prefix here; the difference between “degradable” and “biodegradable” is that while “degradable” products can be broken down by chemical or biological processes, “biodegradable” materials can only be broken down by biological processes.

The concern for biodegradable products began with the issue of microplastics, first detected in the 1970s in the ocean as plastic residue, but not termed “microplastics” until the mid-2000s. (A good and comprehensive article on this by Napper and Thompson was published online in 2020[2].) Many multinational companies have stopped using microplastics (microbeads) in their formulations and other brands are following, but let’s clearly define what are, and are NOT, microplastics! To qualify as a microplastic, four criteria must be met:

1. It must be a polymer
2. It must be solid (at RT)
3. It must be in particulate form
4. It must be under 5mm in size

All four criteria must be met – if even a single one of these four is not present, the substance is NOT considered a microplastic. And to complicate matters further, there are many exclusions even if these four criteria are met, including the following:

1. The material is natural
2. The material is degradable
3. Its solubility is > 2 g/liter
4. No carbon atoms in its chemical structure
5. Its release to the environment is prevented when used
6. Its physical properties are permanently modified during end use
7. It is permanently incorporated into a solid matrix during end use
8. And likely more…

Just because your products may be “natural” does not mean they are “biodegradable” – measurement is key! As mentioned by Dr. Martin Perry, Advanced Development Safety Laboratories, at SCS Formulate in 2021: “Although natural content is good to know, and there is a perception that natural ingredients are more biodegradable than synthetic ones, knowing the biodegradability is important. The natural content of your product or your organic content is not going to be sufficient for you to substantiate anything on biodegradability.”[3]

To be precise, most companies adhere to the standard of “readily biodegradable”, defined as the ability of a product to biodegrade quickly and completely (≥ 60% by OECD 301A-F/ASTM D7373 testing) within 28 days. You might also hear the term “inherently biodegradable,” defined as between 20% and 60% biodegradability as measured by OECD 301A-F testing, but “readily biodegradable” is stricter and preferable.

From the OECD iLibrary: “The OECD Guidelines for the Testing of Chemicals is a collection of about 150 of the most relevant internationally agreed testing methods used by government, industry and independent laboratories to identify and characterize potential hazards of chemicals. They are a set of tools for professionals, used primarily in regulatory safety testing and subsequent chemical and chemical product notification, chemical registration and in chemical evaluation. They can also be used for the selection and ranking of candidate chemicals during the development of new chemicals and products and in toxicology research. This group of tests covers environmental fate and behaviour. In 2017, the section 3 “Degradation and Accumulation” was renamed to “Environmental fate and behaviour” to take into account Test Guidelines measuring endpoints such as dispersion, aggregation.”[4]

As a final note, microplastics and biodegradability concerns are part of a larger issue of minimizing environmental pollution. Some may equate this trend with the apparent discovery of reef damage caused by certain organic sun filters, specifically octinoxate and oxybenzone. There are bans in place on octinoxate and oxybenzone in many countries, including the US (Hawaii, Florida, US Virgin Islands), Aruba, Bonaire (off the coast of Venezuela), Palau and parts of Mexico. However, this is not a biodegradability issue as much as it is a toxicity issue, and the science is still unclear as to the actual effect of residual organic sunscreens on coral reefs.

[1] Focht DD. “Biodegradation”. AccessScience. doi:10.1036/1097-8542.422025.

[2] Napper & Thompson, “Plastic Debris in the Marine Environment: History and Future Challenges”. Global Challenges. doi: 10.1002/gch2.201900081.

[3] https://www.cosmeticsdesign.com/Article/2021/11/18/Biodegradable-beauty-focus-needed-in-natural-and-organics-before-regulatory-change-says-expert#

[4] https://www.oecd-ilibrary.org/environment/test-no-301-ready-biodegradability_9789264070349-en

Ben Blinder is the Executive Director, Business Operations at Gattefossé USA, with P/L responsibility for the personal care and pharmaceutical business units in the US and Mexico. He is also a founding member of the Advisory Committee on Diversity & Inclusion for Gattefossé in North America. Ben holds a BS in chemical engineering from Lehigh University.

Ever since the FDA published their proposed monograph ruling in February 2019 recognizing titanium dioxide and zinc oxide as the only Category I (Safe and Effective) sunscreens, a cascade of reformulations of most sunscreens products on the US market took place.  Inorganic sunscreen formulations are now center-stage and are slowly replacing organic sunscreen formulations.  In fact, the trend started in 2018 when the state of Hawaii proposed a ban on Octinoxate and Oxybenzone stating that these two sunscreens have a negative effect on coral reefs.  Now that the ban is in effect, another bill is proposing to ban sunscreens containing Octocrylene and Avobenzone for the same reasons.  It is true that many regulatory bodies including the FDA did not support the Hawaiian ban, and the Personal Care Product Council (PCPC) is addressing the proposed monograph rulings. All these actions might lead to uncertain outcomes.  In fact, in a few years the US consumers might be limited to the use of products containing inorganic sunscreens only (with the exception of Ensulizole and Ecamsule).  There is some hope that certain Time and Extent (T&E) molecules are being reviewed by the FDA and may be approved for launch.  Bemotrizinol is a front-runner and its use in formulation is quite good as it protects both in the UVB and UVA areas.

Selecting the right inorganic sunscreen

Zinc oxide and titanium dioxide not only refract light but also absorb it.  The refractive index of titanium dioxide is 2.8 whereas that of zinc oxide is only 2.0.  This makes titanium dioxide much more effective at scattering light in a formulation.  From and absorption point of view, zinc oxide and titanium dioxide have conductance bands around 3.4 and 3.1 eV, respectively.  This makes zinc oxide a bit more efficient in protecting against UVA rays and titanium dioxide more efficient at shielding UVB rays.  As particle size decreases you get much more pronounced blue shift due to a change in the band-gap width.  For example, a 0.15 eV blue shift has been reported for 4.7 nm titanium dioxide compared to bulk.

Keep in mind, when particles become smaller than their optimal light scattering size (typically half their wavelength) they become much more transparent.  For example, zinc oxide becomes transparent at below 200 nm whereas titanium dioxide becomes transparent at sizes around 10-20 nm.  This makes formulating with zinc oxide much easier to achieve transparent formulations but harder to reach high SPF due to its performance in the UVB region.

Sometimes the so-called “boosters” can help many formulators resort to using salicylates as UVB boosters in their formulations.  Butyl octyl salicylate is not an approved sunscreen in the US but many formulators use it to boost their inorganic sunscreen SPF while claiming no organic sunscreens added.

Dispersion versus powder

The choice to use inorganic sunscreens as powder or dispersions in formulations is a very polarizing decision and many formulators prefer to use one type over the other.  In general, dispersions claim to have a smaller primary particle size which results in better dispersion of the pigment into the emulsion and leads to higher SPF and less whitening on the skin.  However, dispersions come at about 50% w/w solvent/pigment which limits the flexibility the formulator to tweak the formulation.  In addition, when working with w/o or w/Si formulations, it is harder to control the viscosity of such emulsions when using dispersions.  In these types of emulsions, the viscosity is built by the internal phase (water).  Using dispersions  ultimately increases the amount of external phase and reduces the amount of water used which will make such emulsions less viscous and less stable.

The use of powders, on the on the other hand, gives the formulator a lot of flexibility and reduces the cost of the formulation.  Although, when using powders, it is important to have manufacturing capability to grind the pigments at the factory scale to reduce agglomeration and produce formulations with good aesthetics.

Selecting emulsion type

Most inorganic sunscreen formulations on the market are w/o or w/Si emulsions.  These types of emulsions are much easier to preserve, as you only preserve the internal phase, and their pH does not fluctuate since they are anhydrous.  These types of emulsions inherently have very good water resistance as well.  Some of the drawbacks of w/o emulsions are their greasy feel mainly imparted by the surfactants and co-surfactants used. They tend to be more whitening on the skin and harder to spread.  W/Si emulsion have a superior end-feel, but they are not particularly biodegradable or earth-friendly by today’s standards.  They share the same characteristics as w/o emulsions when it comes to preservation, pH and water resistance.  In general w/Si emulsions are harder to stabilize and require the use of more than one surfactant to obtain stable emulsions.

It is very rare to see o/w emulsion formulations on the market, since they are harder to preserve and stabilize.  The presence of zinc oxide ultimately shifts pH towards 7.5 which renders most preservatives less effective.  In addition, at that pH very few polymers work well at stabilizing such emulsions especially naturally derived polymers.  On the other hand, these emulsions typically have a nicer feel on the skin and could be cost effective.

Adding a film former or SPF booster

Selecting a film-former or SPF booster for the emulsion is a critical step and one that should not be avoided.  The selection of the appropriate polymer depends mostly on the experience of the formulator and the in vivo results previously obtained with such polymer.  Many polymers are marketed to the formulators and some of them could work in one formulation or another.  However, it is crucial that the film former works across many formulations and especially in vivo since such tests are quite costly and hard to schedule.  As scientists, we should always test the formulations in vitro for water resistance and SPF to ensure that the addition of the polymer will give the desired results.  This will enable the formulator to refine the level of polymer in the emulsion as well.

In conclusion, I hope I shed some light on formulating inorganic sunscreen emulsions and I leave it up to the creativity of formulators to create excellent formulations with great aesthetics and high SPF.

Biography

Dr. Fares started his career in personal care studying the effect of solvents on sunscreen chemicals.  His interest in skin drug delivery especially from polymeric matrices grew during his graduate work at Rutgers, where he received his Ph. D.

Dr. Fares worked at Block Drug and GlaxoSmithKline where he held positions in research and development in the areas of skincare and oral care.  After that, he joined L’Oréal where he held several positions of increasing responsibility leading to AVP of skincare.  He is currently the Senior Director of skincare and oral care at Ashland Specialty Ingredients.  Dr. Fares is the author of many publications, and patents and made many presentations in national and international meetings in the areas of suncare, skincare, and oral care.  Dr Fares chairs the NYSCC scientific committee and has won multiple awards in the areas of sun care and polymer chemistry.