Donald L. Bissett
P&G Beauty, Miami Valley Innovation Center, Cincinnati, Ohio, U. S.A.
There are many cosmetic materials that are claimed to have anti-aging effects when used topically. Since there are so many of these materials and since the term anti-aging is very broad (in terms of prevention vs. improvement and the wide array of possible benefit areas such as wrinkling, sagging, texture, sallowness, hyperpigmentation, etc.), this relatively short chapter must necessarily be selective in its scope. Thus, this discussion will focus on only a few classes of cosmetic agents which are reported to have bio-activity to provide wrinkling and/or sagging improvement (i. e., repair or reversal). Particular attention will be directed to those materials within these classes for which there are readily available or published clinical data to support their reported skin appearance improvement benefits.
There are several forms of vitamin A that are used cosmetically. The most widely utilized ones include retinol, retinyl esters (e. g., retinyl acetate, retinyl propionate, and retinyl palmitate), and retinaldehyde. Through endogenous enzymatic reactions, all of these are converted ultimately to trans-retinoic acid (trans-RA), which is the active form of vitamin A in skin. Specifically, retinyl esters are converted to retinol via esterases. Retinol is then converted to retinaldehyde by retinol dehydrogenase. And finally retinaldehyde is oxidized to RA by retinaldehyde oxidase.