Scientific Blog Article

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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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.
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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.

The recent introduction of holistic wellness as a major component of “I feel better and I look better” is not new to the beauty and cosmetic market. However, the explosion of nutritional formulations in the space of beauty from within is today associated with more robust and convincing scientific evidence than in the past. Supplement formulations appear more complex and not limited to collagen, vitamins and minerals to cite some of the most popular ingredients. The introduction of phytochemicals, sometime in the form of standardized plant extracts, along with vitamin and minerals, is providing an increased targeting and holistic approach to inner mechanisms associated with stress, diet, metabolism, aging, etc. that eventually influence our external look. This is not surprising as our cosmetic targets such as skin, hair, nail are part of our body and therefore react to our body unbalance. The connection between our gut and our skin, when a diverse gut environment is associated with skin conditions such as acne, psoriasis, atopic dermatitis, etc.¹ and the influence of hormonal and stress-induced changes that can trigger hair conditions such as androgenetic alopecia and telogen effluvium.² are some examples.

Modern formulations would use a wide range of ingredients that, when ingested, specifically target biological mechanisms associated with our health and wellness as well as our look (and I underline the specificity). It is possible then to create formulation that when tested deliver real efficacy and stand up to the claims.

Natural ingredients are taking center stage in these formulations, also inspired by the use of naturals in traditional medicine, with the possibility to merge knowledge from the western and eastern world.

When having a closer look at the applications and studies of supplements targeting wellness and beauty, recent reviews have highlighted their use as adjuvants and/or treatment for different dermatology or cosmetic conditions such as hair loss, acne, skin aging^3-5. Since supplements are not FDA regulated, large, peer-reviewed clinical studies are necessary to determine the efficacy and safety of these supplements, especially since most of them haven’t been clinically tested. To avoid running lengthy and sometime expensive clinical trial, product manufacturers often rely on supplier’s data and/or academic literature about the ingredients in the final supplement composition. However, it is necessary to test the finish product since ingredient’s dosage and ingredients interaction and/or synergy can determine the outcome both from a safety and efficacy point of view. The quality of the clinical study is also important (number of subjects, inclusion/exclusion criteria, end points measures, data significance). Finally, Institutional Review Boards (IRB) approval is becoming increasingly in demand prior to the clinical study especially if dealing with compositions that are new to the market and carry some safety risk, and is often requested by scientific journals when trying to publish the data.

In conclusion, the cosmetic and the nutrition (supplements) industry are getting closer, with beauty as a shared target. Innovative supplement formulations carrying high end natural ingredients are becoming popular and demanded by the market. Rigorous science and testing is mandatory to make sure the formulation can survive scrutiny by the consumers and the FDA. Combination of topical and ingestible treatments in the beauty market will continue to grow in the following years.

1. Ellis SR, Nguyen M, Vaughn AR, Notay M, Burney WA, Sandhu S, Sivamani RK. The Skin and Gut Microbiome and Its Role in Common Dermatologic Conditions. Microorganisms 7(11):550, 2019
2. Hadshiew IM, Foitzik K, Arck PC, Paus R. Burden of hair loss: stress and the underestimated psychosocial impact of telogen effluvium and androgenetic alopecia. J Invest Dermatol. 123(3):455-7, 2004
3. Adelman MJ, Bedford LM, Potts GA. Clinical efficacy of popular oral hair growth supplement ingredients. Int J Dermatol 60(10):1199-1210, 2021
4. Clark AK, Haas KN, Sivamani RK. Edible Plants and Their Influence on the Gut Microbiome and Acne. Int J Mol Sci 17;18(5):1070, 2017
5. Sardana K, Sachdeva S. Role of nutritional supplements in selected dermatological disorders: A review. J Cosmet Dermatol 21(1):85-98, 2022

Giorgio Dell’Acqua

Giorgio Dell’Acqua is Nutrafol’s Chief Scientific Officer. Part of the Leadership team, Giorgio spearheads the brand innovation, product formulation and scientific communication. 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 22 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, including La Prairie and Kiehl’s. He has helped bringing more than 200 successful active ingredients and finished products to market, has authored more than 80 publications in medicine and cosmetic science, he holds 2 patents and has been a keynote speaker on clean beauty and natural ingredients. Giorgio serves on the NYSCC board as advisor.

1. Brief history of nanomaterial regulations

 According to Wikipedia, the word “nanotechnology” was first coined by Professor Norio Taniguchi of Tokyo University in 1974. He used it to describe semiconductor processes such as thin film deposition and ion beam milling, which exhibit characteristic control on the order of a nanometer.  Since the 1980s, the term nanotechnology has been referring to the fabrication, use/manipulation, control and characterization of structures devices or materials with a least one dimension in the size range of 1–100 nm. ^1,2

Nanotechnologies represent a fast-growing market, bringing with them a combination of benefits, promises, risks, and uncertainties.  It is synonymous with high technology and high efficacy. It has often been used as a buzzword in advertisements and label claims of many consumer products, including personal care products, to gain attention.  Various physical and chemical properties of a material can be affected by its particle size. Nanomaterials have been engineered to have enhanced properties and performance that are beyond their non-nano counterparts. However, these much enhanced properties also raises questions about their safety.

In June 2007, the safety of nanomaterials such as nano TiO₂ in sunscreen and fulluerene was raised in the article, Nanotechnology, the untold promise, and unknown risk, in Consumer Reports.  In August 2007, Friend of Earth (FOE) published Technology and Sunscreens, raising the particular concern over nano TiO₂ and ZnO in sunscreens and calling for labeling and regulation of nanomaterials in consumer products. Earlier in 2006, a coalition of environmental and consumer groups, including the International Center for Technology Assessment, Friends of the Earth, and Our Bodies, Ourselves, filed a legal petition with the Food and Drug Administration (FDA) asking FDA to regulate nanotechnology.

The first regulatory move was made by European Commission (EC).   EC acknowledged the safety concerns considering that nanomaterials could have very different physical and chemical properties over their non-nano counterparts, potentially resulting in different toxicological profiles. In 2005, the EU Scientific Committee on Consumer Products was requested by EC to provide a scientific opinion on the safety of nanomaterials in cosmetic products, in particular, the appropriateness of existing methodologies to assess the potential risk associated. This created public fear regarding nanomaterials in consumer products, especially in personal care products. In the meantime, the uncertainty of the future regulatory landscape made it extremely difficult for cosmetic formulators to incorporate nanomaterials in any formulation.

In 2009, REGULATION (EC) No 1223/2009 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 30 November 2009 on cosmetic products stated the purpose and need of a definition of nanomaterial, which has been evolving since. Most recently, COMMISSION RECOMMENDATION of 10 June 2022 on the definition of nanomaterial, C 229/1, defines nanomaterial as follows:

Nanomaterial means a natural, incidental, or manufactured material consisting of solid particles that are present, either on their own or as identifiable constituent particles in aggregates or agglomerates, and where 50 % or more of these particles in the number-based size distribution fulfill at least one of the following conditions:

– one or more external dimensions of the particle are in the size range 1 nm to 100 nm;
– the particle has an elongated shape, such as a rod, fibre or tube, where two external dimensions are smaller than 1 nm and the other dimension is larger than 100 nm.
– the particle has a plate-like shape, where one external dimension is smaller than 1 nm and the other dimensions are larger than 100 nm

Moreover, Article 16 of Regulation (EC) No 1223/2009 on cosmetic products requires that, in addition to the notification under Article 13, cosmetic products containing nanomaterials shall be notified to the Commission by the Responsible Person using electronic means six months prior to being placed on the market. Notification should be done on Cosmetic Products Notification Portal (CPNP).

2. Interpretation of nanomaterial definition:

The interpretation of the nanomaterial definition depends to a large extent on the size measurement method. Because of the structural complexity of nanomaterials, no single test method is capable of measuring all nanomaterials precisely and properly. EC recommends determining nanomaterial by its primary particle size or internal structure while allowing sectoral interpretation according to the actual use conditions, which may vary drastically from industry to industry.

In 2011, Cosmetic Europe issued their own interpretation of EC definition of nanomaterial, and then an update in 2019, stating that “materials with constitutive elements having a dimension in the nano-range (e.g. aggregates, agglomerates, composites) but that are themselves greater than 100 nm in size should not be considered as nanomaterials unless they release nano-objects or aggregates of less than 100 nm in size in cosmetic products under normal use conditions”.  Accordingly, the size of aggregates or agglomerates is used to determine the nanomaterial for labeling cosmetic products. This interpretation has been followed by many cosmetic companies.

3. Commercial use of nanomaterials

According to a EC’s report, Sub-working group of on nanomaterial definition, published on January 28, 2021, 37,647 cosmetic products were notified with nanomaterials in EU market, (via Art.13 procedure), which corresponds to about 1.5% of all notifications. According to 2015 – 2020 data, on average, about 10 new cosmetic products containing nanomaterials are placed on the EU market every day.

Most common product categories with nanomaterials: (64% of all nanomaterials notifications):

1. Sun protection
2. Nail varnish/nail make up
3. Oxidative hair care
4. Foundation
5. Lip care products and lipsticks

The most used cosmetic ingredients are reported below (4 ingredients accounts for over 70% of all CPNP notifications):

1. Titanium Dioxide
2. Silica Dimethyl Silylate, Silane, dichlorodimethyl-, reaction products with silica
3. Carbon Black nano (CI77266)
4. Silica

Scientific Committee for Consumer Safety (SCCS) under European Commission is requested by EC to evaluate the safety of the listed nanomaterials via a process that was based on the scientific literature available at the time and SCCS’ expert judgment. In early 2021, SCCS published an advice on the safety of nanomaterials in cosmetics, in which nanomaterials of concern were separated into two groups. ³

     — 16(4) of the Cosmetics Regulation

28 substances including silica, Titanium dioxide, Zinc oxide, Methylene Bis Benzotriazolyl Tetramethylbutylphenol were listed in the appendix 1 in an order of priority according to risk potential (based on a number of criteria).

     — 16(6) of the Cosmetics Regulation

SCCS reviewed three previous inclusive opinions on colloid silver, nano styrene/acrylate polymer and nano silica, and identified certain aspects relating to each of these nanomateirals that raised safety concern.

4. Nano TiO₂ /ZnO in sunscreens

For personal care products, nano TiO₂ and ZnO are perhaps the two most concerning ingredients due to their wide use as sunscreen actives. Because of their very small primary particle size, nano TiO₂ and ZnO are much more transparent on the skin and much more potent in UV protection than their non-nano or pigmentary counterparts. For instance, pigmentary TiO₂ is known to be completely opaque and cannot be used in any skin care product for effective UV protection.  Nano TiO₂, with a primary size of 10 – 20 nm, is not only highly transparent but also provides 5 – 6 times higher SPF.   For this reason, nano TiO₂ and ZnO have been used widely in sunscreen products in Japan and Australia since 1980s.  They have been popular among those having sensitive skin and allergic to organic sunscreens.

Up to now, and after the use by hundreds of millions of consumers, there have been no reports of any adverse health effects for nano TiO₂ and ZnO. However, they were still put under great scrutiny due to the general concerns and fear that were raised for nanomaterials in early 2000s.  Many customers, especially in EU, became somewhat nanophobic at the time as the future of regulatory landscape remained uncertain.

For topical application, the major concern is transdermal adsorption or penetration.  After years of study, SCCS issued in 2012 OPINION ON Zinc oxide (nano form) COLIPA S76 stating that “There is no evidence for the absorption of ZnO nanoparticles through skin and via the oral route. Even if there was any dermal and/or oral absorption of ZnO nanoparticles, continuous dissolution of zinc ions would lead to complete solubilization of the particles in the biological environment.” ⁴ Two years later, the SCCS issued the OPINION ON 22 on Titanium Dioxide (nano form), stating “the main consideration in the current assessment is the apparent lack of penetration of TiO₂ nanoparticles through skin.” ⁵

Another concern is photo-catalytic activity of nano TiO₂ that lead to generation of free radicals and ensuing oxidation.  Surface treatment of nano TiO₂ had been quite common, and the data collected by SCCSs on commercial grades confirmed that the photo-catalytic activity could be much suppressed by surface treatment.

Finally, EU revised the nano TiO₂ monograph for use as UV filters in 2016. The key updates included a list of allowed surface treatments and a limit on the photocatalytic activity. In the same year, ZnO was officially approved as an UV filter, and a list of surface treatments and solubility specification were included in the monograph. ⁶

After years of investigation, EC finally concluded that nano TiO₂ and ZnO were safe for personal care use as long as:

1. They comply with the specifications in the EU monographs.
2. The final product will not lead to exposure of the end-user’s lungs by inhalation.

For other nanomaterials under review, the SCCS has yet to establish final opinions. The future regulatory status remains uncertain.

5. Regulations in other regions

Nanomaterial is generally defined as a material with internal or external dimensions in the range of 1 – 100 nm in other regions.   Many regulatory agencies share similar concerns to EC’s, but they have not acted as swiftly as EC.  Although there are guidelines for considering the safety of nanomaterials, there are few laws enacted to regulate them.  To the author’s knowledge, there are two regulations outside EU:

A) Canada – If a sunscreen product contains only inorganic UV filters, nano TiO₂ and/or ZnO, it is considered a Natural Health Product, for which the premarket approval is not needed. However, if any of the two is used with organic UV filters, the sunscreen is a drug product. Safety of nano TiO₂/ZnO needs to be addressed and approved, which can be painstaking. Further, there is no official test method and threshold for classifying nanomaterials.

B) China – “Regulations on the Supervision and Administration of Children’s Cosmetics” issued by the State Food and Drug Administration (2021 No. 123), was issued in 2021. Section 7.1 states that:

“….. New raw materials that are still in the monitoring period should not be used, and raw materials prepared by new technologies such as genetic technology and nanotechnology should not be used. If there is no alternative raw material that must be used, the reason should be explained, and evaluate the safety of children’s cosmetics”.

Since nano TiO₂ and ZnO are not new technologies, they could be exempted from this regulation. However, the ambiguity in interpreting the regulatory language and difficulty in effective communication with Chinese officials have made many company shy away from nano TiO₂ or ZnO, and instead turning to the non-nano grades.

6. Summary

Nanomaterial safety and regulations are important to personal care product development. Many nanomateterials used in our industry are under safety review and their future is uncertain. As far as nano TiO₂ and ZnO are concerned, it is official that they are safe as long as they are not exposed to end-users’ lung in application. Due to the complex structures of nanomaterials, their size analysis method, data interpretation and regulatory classification have been constantly investigated and are still evolving. Formulators are highly advised to consult with their regulatory experts as well as the suppliers when choosing nano or non-nanomaterials.

References:

1. (2007a) Opinion on: the Scientific Aspects of the Existing Proposed Definition Relating to Products of Nanoscience Nanotechnologies. Brussels: European Commission Health Consumer Protection Directorate General.
   SCENHIR. (2007b) Opinion on: the Appropriateness of the Risk Assessment Methodology in Accordance with the Technical Guidance Documents for the New and Existing Substances for Assessing the Risk of Nanomaterials. Brussels.

2. ISO/TS 27687. (2008). Nanotechnologies – Terminology and Definitions for Nano-objects – Nanoparticle, Nanofibre and Nanoplate.
3. SCCS/1618/2020 Scientific Advice; https://health.ec.europa.eu/system/files/2022-08/sccs_o_239.pdf
4. SCCS/1489/12; https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_103.pdf
5. SCCS/1516/13 Revision of 22 April 2014; https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_136.pdf
6. COMMISSION REGULATION (EU) 2016/1143 of 13 July 2016, amending Annex VI to Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products