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The Use of Natural Oils to Treat the Skin

by james.runkle@drummondst.com

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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