M. Elizabeth Briden
Advanced Dermatology and Cosmetic Institute, Edina, Minnesota, U. S.A. Barbara A. Green
NeoStrata Company, Inc., Princeton, New Jersey, U. S.A.
By definition, to exfoliate is to remove the surface in scales or laminae. Therefore, classical exfoliants are those agents that work at the skin’s surface causing the removal of skin in layers. Exfoliation is characterized, based on its mechanism of action, into 3 categories:
1. physical/manual (loofah or microdermabrasion)
2. chemical/keratolytic agents (e. g., salicylic acid)
3. natural/exuviation (e. g., alpha-hydroxy acids)
Manual or physical exfoliation involves the use of physically abrasive devices such as loofahs and could also include instrumental techniques such as microdermabrasion. Manual exfoliants physically scrape and remove surface skin cells.
Salicylic acid represents the chemical/keratolytic class of exfoliants. Recent reviews of salicylic acid propose a change to the term “desmolytics” to more accurately reflect the action of these materials on skin (1,2); these agents dissolve the desmosomal bonds between cells beginning at the uppermost skin layers providing exfoliative effects from the top of the skin downward in a non-specific manner (1-5).
Natural exfoliation, also known as exuviation, is the naturally occurring process of epidermal turnover, which occurs approximately every 28 days. Compounds that enhance the natural process of exuviation include, the alpha-hydroxy acids (AHAs), polyhydroxy acids (PHAs), and bionic acids. These agents are frequently considered exfoliants; however, their effects differ from those of conventional keratolytics or desmolytics (6,7). They target the base of the stratum corneum, the layer identified as the stratum dysjunctum, and function by diminishing bonding strength between cells in a specific manner leading to normalization of cell turnover and, thus, exfoliation (6,8).
This chapter discusses the mechanisms, effects and formulating considerations of exfoliants, including physical implements, microdermabrasion, exuviating compounds (AHAs, PHAs, bionic acids), the keratololytic/desmolytic salicylic acid, and finally a newly emerging, non-acid, acetyl amino sugar known as N-acetylglucosamine.