Non-surgical skin care and rejuvenation

Introduction

Skin care involves several basic hygiene activities that include cleansing and moisturizing. With advancements in the understanding of skin physiology, more effective moisturizers have been developed that contain ingredients designed to improve the appearance and functioning of the skin. These products are known as cosmeceuticals; however, from a regulatory standpoint, there is no such category. Cosmeceuticals are simply cosmetics, usually with a moisturizer base and some added “hero” ingredient that may be called “active” because it imparts some added benefit to the skin. These specialty ingredients are usually vitamins, botanicals, or proteins that are generally recognized as safe and therefore do not require any regulatory oversight.

Basic to skin care is an understanding of the different skin types, each with unique skin care cares. There are many classifications for skin type based on the degree of wrinkling, skin color, amount of sebum production, etc. The classification that seems most helpful is the Fitzpatrick skin type classification system based on erythema and tanning reactions to the first sun exposure in early summer ( Table 7.1 ).

Based on this skin typing system, recommendations can made for sun protection and appropriate formulations can be selected for cleansing and moisturization. It is interesting to note that there are physiologic differences between the various Fitzpatrick skin types. The differences are summarized in Table 7.2 . While the corneocyte surface is the same, there are 20 stratum corneum cell layers in African-American skin as compared with 16 cell layers in Caucasian skin. The desquamation rate for African American skin is 2.5 times that of Caucasian skin, perhaps accounting for the increase in skin ashiness, accompanied by the pigmentation of the desquamating skin scale. However, the stratum corneum lipid content is higher in African Americans than Caucasians, but the ceramide level is lower. As expected, melanophage and mast cell granule size is larger in African-American skin. These unique differences may account for some of the dermatologic issues observed and can be addressed in customized skin care for the unique needs of all skin types.

Despite all of these differences, it is important to note that the number of melanocytes per unit area of skin does not vary across ethnicities. Instead, it is the relative amount of melanin packaged into melanocytes that accounts for the physiologic differences between Caucasian skin and ethnic skin. There are pronounced differences in photoaging between the various Fitzpatrick skin types based on the ability to withstand reactive oxygen species generation by photoradiation. Ten percent of the UVB radiation penetrates to the dermis, accounting for sunburn; however, the mean transmission into the dermis by Fitzpatrick type VI skin is 5.7%, compared with 29.4% for Fitzpatrick type I and II skin. Similarly, 50% of the UVA radiation penetrates to the papillary dermis; however, the mean transmission for Fitzpatrick type VI skin is 17.5%, as compared with 55% for Fitzpatrick skin type I and II. This difference is due to the basal cell layer functioning as the main site for UV filtration in Fitzpatrick type VI skin while the stratum corneum functions as the site for UV filtration in Fitzpatrick skin types I and II. The basal cell layer removes twice as much UV radiation as the stratum corneum.

Based on these unique skin needs, we can then better understand how to address cleansing, moisturizing, retinoids, and sun protection for persons of all skin types.

Cleansers

Cleansing is perhaps the most profound of all activities undertaken for skin hygiene and beautification. Cleansing is necessary after all surgical procedures to prevent infection and optimize wound healing, but cleansing of the face and other body areas is also undertaken on daily basis by most individuals. Cleansing requires a delicate balance between skin hygiene and stratum corneum barrier damage. The act of cleansing is a complex physical and chemical interaction between water, detergent, and the skin. During cleansing, micelles are created with external hydrophilic groups surrounding an internal lipophilic pocket. These micelles can surround oily substances, such as sebum, dispersing the oil in water for removal and rinsing.

Cleansers are based on surfactants and are the primary cause of dry skin. This arises because surfactants cannot distinguish between lipophilic skin soils requiring removal and the lipophilic intercellular lipids required for barrier maintenance. The bipolar structure of skin soils is similar to the fatty acids, cholesterol, and ceramides comprising the lipid bilayers of the stratum corneum. Cleanser barrier damage leads to alterations in stratum corneum function and desquamatory failure with increased corneocyte retention. This is the mechanism by which cleansers induce the rough, scaly appearance characteristic of dry skin.

The cleanser component that causes dry skin is the high-charge density of the carboxyl head group, which promotes strong protein binding. This characteristic insures excellent cleansing and removal of protein soils, but damages the stratum corneum proteins, denatures enzymes, and alters corneocyte water holding of the capability. Barrier damage is also influenced by cleanser pH. Soap typically has an alkaline pH of 10–11, producing skin protein swelling and ionization of the lipid bilayers. Thus, synthetic detergents with more neutral pH of 5–7 minimize barrier damage and are the preferred cleanser.

There are many different types of cleansers available for purchase with unique compositions and specific skin benefits. The term soap is used loosely to refer to any cleanser; however, this is not correct, as soap denotes a specific chemical entity. Soap is created when a fat interacts with an alkali, resulting in a fatty acid salt with detergent properties. Modern commercial soaps are a blend of tallow and nut oil, or the fatty acids derived from these products, in a ratio of 4:1. Altering the ratio modifies the cleansing ability of the formulation. For example, increasing this ratio results in “superfatted” soaps touted for their cleansing “mildness.” It is the excess fatty acid that reduces the ability of the cleanser to remove lipids, thus these products are marketed as “sensitive skin” cleansers. These soaps can be packaged as bars or liquids.

The most common cleanser formulations marketed today are composed of synthetic detergents, known as syndets, and possess a lower alkaline pH, resulting in less removal of intercellular lipids. Soaps typically have a pH of 9–10 while syndets are formulated at a pH of 5.5–7, closer to the natural neutral skin pH (Dove Soap, Unilever). It is possible to combine both soap and syndet cleansers into a formulation known as a combar, providing better cleansing with less lipid disruption (Dial Bar, Henkel).

Bar cleansers are the most widely used form of cleanser, with many different types of bar cleansers available, as summarized in Table 7.3 . The typical bar cleanser composition is a combination of two surfactants: the soap alkyl carboxylate and the syndet acyl isethionate. Alkyl carboxylate and acyl isethionate are both anionic surfactants, but the carboxylate group is most damaging, binding and denaturing stratum corneum proteins. Liquid cleansers have a composition similar to bar cleansers, except they are poured from a bottle.

There are a variety of different cosmeceutical cleansers that are currently available and will be briefly discussed by type.