Author: james.runkle@drummondst.com

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

1. McMullen R, Dell’Acqua G. History of natural ingredients in cosmetics. Cosmetics. 2023;10:71.
2. McMullen R. Antioxidants and the Skin (2nd edition). Boca Raton, FL: CRC Press; 2019.
3. Garavaglia J, Markoski M, Oliveira A, Marcadenti A. Grape seed oil compounds: biological and chemical actions for health. Nutr Metab Insights. 2016;9:59-64.
4. Prottey C, Hartop P, Press M. Correction of the cutaneous manifestations of essential fatty acid deficiency in man by application of sunflower-seed oil to the skin. J Invest Dermatol. 1975;64(4):228-34.
5. Hansen A, Haggard M, Boelsche A, Adam D, Wiese H. Essential fatty acids in infant nutrition. III. Clinical manifestations of linoleic acid deficiency. J Nutr. 1958;66(4):565-76.
6. Lin T, Zhong L, Santiago J. Anti-inflammatory and skin barrier repair effects of topical application of some plant oils. Int J Mol Sci. 2018;19:70.
7. Parnsamut N, Kanlayavattanakul M, Lourith N. Development and efficacy assessment of tea seed oil makeup remover. Ann Pharm Fr. 2017;75(3):189-95.
8. Ishak W, Katas H, Yuen N, Abdullah M, Zulfakar M. Topical application of omega-3-, omega-6-, and omega-9-rich oil emulsions for cutaneous wound healing in rats. Drug Deliv Transl Res. 2019;9(2):418-33.
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.
11. Farag M, Gad M. Omega-9 fatty acids: potential roles in inflammation and cancer management. Genet Eng Biotechnol. 2022;20(1):48.
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.
19. Barcelos R, de Mello-Sampayo C, Antoniazzi C, Segat H, Silva H, Veit J, et al. Oral supplementation with fish oil reduces dryness and pruritus in the acetone-induced dry skin rat model. Dermatol Sci. 2015;79(3):298-304.
20. Sawada Y, Saito-Sasaki N, Nakamura M. Omega 3 fatty acid and skin diseases. Front Immunol. 2021;11:623052.
21. Miura K, Way M, Jiyad Z, Marquart L, Plasmeijer E, Campbell S, et al. Omega-3 fatty acid intake and decreased risk of skin cancer in organ transplant recipients. Eur J Nutr. 2021;60(4):1897-905.
22. Martins A, Gomes A, Vilas Boas I, Marto J, Ribeiro H. Cannabis-based products for the treatment of skin inflammatory diseases: a timely review. Pharmaceuticals (Basel). 2022;15(2):210.
23. Vaughn A, Clark A, Sivamani R, Shi V. Natural oils for skin-barrier repair: ancient compounds now backed by modern science. Am J Clin Dermatol. 2018;19(1):103-17.
24. Blaak J, Staib P. An updated review on efficacy and benefits of sweet almond, evening primrose, and jojoba oils in skin care applications. Int J Cosmet Sci. 2021;44(1):1-9.
25. Badiu D, Rajendram R. Chapter 33 – Effect of olive oil on the skin. In: Preedy V, Watson R, editors. Olives and Olive Oil in Health and Disease Prevention (Second Edition). London, UK: Academic Press; 2021. p. 401-13.
26. Moore E, Wagner C, Komarnytsky S. The enigma of bioactivity and toxicity of botanical oils for skin care. Front Pharmacol. 2020;11:785.
27. Cooke A, Victor S, Cork M, Lavender T. Topical oils for the prevention or treatment of dry skin in term infants. Cochrane Database Syst Rev. 2019;2019(11):CD011100.
28. Aksucu G, Azak M, Çağlar S. Effects of topical oils on neonatal skin: a systematic review. Adv Skin Wound Care. 2022;35(12):1-9.
29. Pupala S, Rao S, Strunk T, Patole S. Topical application of coconut oil to the skin of preterm infants: a systematic review. Eur J Pediatr. 2019;178(9):1317-24.
30. Chiabi A, Kenmogne M, Nguefack S, Obadeyi B, Mah E, Meka F, et al. The empiric use of palm kernel oil in neonatal skin care: justifiable or not? Chin J Integr Med. 2011;17(12):950-4.
31. Danby S, AlEnezi T, Sultan A, Lavender T, Chittock J, Brown K, et al. Effect of olive and sunflower seed oil on the adult skin barrier: implications for neonatal skin care. Pediatr Dermatol. 2013;30(1):42-50.
32. Karagounis T, Gittler J, Rotemberg V, Morel K. Use of “natural” oils for moisturization: review of olive, coconut, and sunflower seed oil. Pediatr Dermatol. 2019;36(1):9-15.
33. Viljoen J, Cowley A, du Preez J, Gerber M, du Plessis J. Penetration enhancing effects of selected natural oils utilized in topical dosage forms. Drug Dev Ind Pharm. 2015;41(12):2045-54.
34. van Zyl L, du Preez J, Gerber M, du Plessis J, Viljoen J. Essential fatty acids as transdermal penetration enhancers. J Pharm Sci. 2016;105(1):188-93.
35. Leung D, Elias P, Nadeau K, Berdyshev E. Olive oil is for eating and not skin moisturization. J Allergy Clin Immunol. 2021;148(2):652.

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.