Although there are many hydroxy acids, the focus of this chapter is on alpha-hydroxyacids, or AHAs as they have come to be known universally since their explosive takeover of the cosmetic facial moisturizer market in the early 1990s [1-3]. More recently, other classes of hydroxyacids have been used in skin care products [4], but at the time of writing (2001) AHAs stand alone as the only hydroxyacids supported by placebo-controlled clinical testing. In fact it is one particular AHA, glycolic acid, that was used in the first AHA facial moisturizers and remains the most common form today. As detailed herein, glycolic acid and other AHAs do more than moisturize. They are able to reduce wrinkles, eliminate fine lines, improve skin surface texture, and lessen some of the other changes associated with photodamaged skin. However, the AHA story starts long before the spectacular appearance of glycolic acid “anti-aging” skin creams in 1992. Some 25 years earlier, another alpha-hydroxyacid, lactic acid, was identified as a component of the skin’s natural moisturizing factor (NMF) and introduced as a moisturizing ingredient in creams and lotions to treat and prevent dry skin, particularly winter dry skin on the hands, legs, and body [5]. At about the same time Van Scott and Yu reported that alphahydroxy acids as a class were effective for treating ichthyosis and other disorders of keratinization [6]. The new information

about AHAs prompted increased interest in glycolic acid by dermatologists for chemical peel procedures. Glycolic acid solutions (50-70% concentration without neutralization) were found to be very effective as acid peels, easier to use and without side effects compared to other peeling agents [7].