CHAPTER 47 Cosmeceuticals and Skin Care
Products applied to the skin can range from purely cosmetic products to prescription drugs, but many fall somewhere in between and are commonly referred to as cosmeceutical agents. The term cosmeceutical is widely used in the skin care industry but is still not recognized by many regulatory bodies such as the U.S. Food and Drug Administration (FDA). However, cosmeceuticals are a reality, as evidenced by the widespread use of this term and a growing number of textbooks and symposia in the medical aesthetics field on this subject. The share of the skin care market comprising cosmeceuticals continues to grow and is the fastest-growing segment of skin care products in the marketplace.
Definitions
The term cosmeceutical was coined by Dr. Albert M. Kligman in the 1970s to focus on the ill-defined territory that falls between cosmetic products and therapeutic medications (drugs). Historically, topical skin care products have been divided into either cosmetics or drugs as defined by the Food, Drug and Cosmetic Act of 1938. A cosmetic is defined as “an article intended to be rubbed, poured, sprinkled, sprayed on, introduced into or otherwise applied to the human body or any part thereof for cleansing, beautifying, promoting attractiveness or altering appearance.” The definition of a drug is “an article intended to affect the structure or any function of the body or articles intended for use in the diagnosis, cure, mitigation, treatment or prevention of disease in man.” At a fundamental level, cosmetics alter the appearance of the skin, whereas drugs alter the structure and function of the skin.
Cosmetics do not require premarketing clearance, and it is up to the manufacturer to ensure that the ingredients and amounts used are not subject to drug regulations and that the product is safe when used as intended. On the other hand, drugs are subject to extensive premarketing research to prove their efficacy and safety. According to regulators, the intended use of a product can also determine its classification. Thus it is not only the ingredients in a skin care product but the claims in labeling and advertising that can affect its classification as a cosmetic or drug. Cosmeceuticals bridge the gap between cosmetics and drugs and refer to products that achieve cosmetic results by means of some degree of physiologic action. Other terms for cosmeceuticals are performance cosmetics, active cosmetics, functional cosmetics, and dermoceuticals.
Cosmeceutical Classes
Categories of cosmeceuticals, some of which overlap, include the following:
Retinoids
The retinoids are compounds that have the basic core structure of vitamin A and its derivatives. All-trans retinoic acid is the active form of vitamin A in the skin. It works by interacting with nuclear receptor proteins to form complexes that interact with DNA sequences to affect transcription and regulation of gene expression for skin keratinocyte growth and differentiation. This causes increased cell turnover in the epidermis. All-trans retinoic acid is quite irritating to the skin and has teratogenic effects. Derivatives such as retinol are commonly used in skin care products because they are have a lower irritation profile and fewer safety concerns. Once applied to the skin, retinol converts to retinaldehyde and then all-trans retinoic acid. The science and benefits of retinoids are well documented, with proven results in reducing photodamage and fine lines of the skin as well as efficacy against acne and psoriasis.
Exfoliants
The two key exfoliant cosmeceuticals are alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). The difference in their chemical structures leads to significant differences in their mechanisms of action, although both cause superficial skin cells to desquamate at an increased rate. This results in a smoothing of skin texture and reduction in photodamage.
Alpha Hydroxy Acids
The most widely used AHA in skin care products is glycolic acid because of its excellent penetration into the epidermis due to its small molecular size. However, lactic acid and other larger AHAs are found increasingly in skin care products. There are many studies on the science and effectiveness of AHAs since the introduction of these products in 1974 by Van Scott and Yu. The AHAs cause desquamation of skin cells in the epidermis by reducing cellular cohesion between keratinocytes. It is postulated that AHAs bind calcium, which decreases local calcium ion concentrations from cell adhesion molecules, thus disrupting intercellular adhesion and increasing exfoliation. There are also some stimulating effects on the dermis, including increased synthesis of collagen and glycosaminoglycans, which also results in a moisturizing effect.
AHAs are very effective in the treatment of photodamaged skin as well as dry skin, seborrheic dermatitis, acne, and keratoses. Concentrations up to 10% are used in home care products, whereas higher concentrations are used in professional treatments.
Beta Hydroxy Acids
Salicylic acid is the only BHA used extensively in skin care products. It has proven keratolytic effects and affects only the stratum corneum. It decreases cohesion between the corneocytes by denaturing glycoproteins and disrupting desmosomal attachments. It has been used to treat hyperkeratotic conditions such as corns, warts, seborrheic dermatitis, psoriasis, and dandruff. Because salicylic acid is lipophilic, it is also very useful in the treatment of acne, and in treatment of photoaging and dyschromia. Concentrations of 0.5% to 2% are commonly used in home care products. The concentration is usually limited by the amount of irritation it causes.
Vitamins
Vitamin C
Vitamin C is a valuable topical cosmeceutical in skin care with significant data supporting its biologic activity and benefits to the skin. Vitamin C is useful in treating photoaging because it has an antioxidant effect as well as a skin-lightening effect through tyrosinase inhibition. It is also an essential cofactor for collagen production in the skin and has proven effects on wrinkle reduction. In addition, vitamin C is helpful in treating acne because of its anti-inflammatory properties due to deactivation of some factors responsible for the production of certain proinflammatory cytokines. The active form of vitamin C is L-ascorbic acid, which is a challenge to incorporate in topical products because of stability and absorption issues. It oxidizes easily, which leads to loss of potency, and it has poor skin penetration. Enhanced delivery systems and use of more stable derivatives such as magnesium ascorbyl phosphate make the use of topical vitamin C a mainstay in skin rejuvenation treatments.
Vitamins B and E
Vitamin B3 (niacinamide) is used topically in skin care because it is well absorbed and well tolerated. The mechanism of action is not well elucidated, but it is a precursor to enzyme cofactors important in many cellular metabolic functions. There is some evidence that it improves the skin barrier function, which reduces skin redness and irritation. It may also reduce hyperpigmentation and improve skin texture and wrinkle depth.
Vitamin E (i.e., the tocopherols) is an anti-oxidant that is a well-documented free radical scavenger. In topical application to skin, there is good evidence that is it photoprotective, helping prevent damage from ultraviolet (UV) radiation. There is some controversy about its use in wound healing and scar prevention, and it may have some benefit in treatment of photodamaged skin.
Antioxidants
Antioxidants protect the skin from free radical damage due to oxidant stress generated by sunlight and pollutants. The mechanism of action is the scavenging of singlet oxygen and reactive oxygen species. Many antioxidants have proved effective when taken orally, but not all are effective topically. The challenge is to get sufficient skin absorption of the correct form of the antioxidant agent with enough activity to achieve the desired effect. In addition to the following agents, some of the vitamins reviewed earlier are also antioxidants.
Ubiquinone
Ubiquinone, or coenzyme Q10, has been proven to absorb after topical application to skin. There are some studies to support improvement in photoaging of skin as well as decreased stratum corneum cell size due to a lessening of the slowdown of cell division that occurs with intrinsic aging.
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