Pharmacological Effects of Alpha-Hydroxy Acids (AHAs) on Human Skin

Abstract

Alpha-hydroxy acids (AHAs) are carboxylic acids characterized by a hydroxy group on the α carbon atom of the molecules. The constituents of AHAs include glycolic acid, lactic acid, malic acid and tartaric acid. The profound effect of AHAs on disorders of keratinization was first to report by Van Scott and Yu in 1974. Recently, medium concentrations of AHAs have been used in the chemical peeling of photo-aged skin, acne and some skin disorders in Japan. However, the overall knowledge of the pharmacological actions of AHAs on the human skin remains insufficient. I herein briefly reviewed our data and the most recently reported information. The principal action of lower concentrations (5-12%) of AHAs, when applied topically to human skin, is based on an accelerated detachment of corneocytes. The pharmacological effects of a medium concentration (15-30%) of AHAs are a thickening of epidermis, a decreased number of atypia in basal cells, an increase in the amount of acid mucopolysaccharides in the papillary dermis, and an increased expression of factor XIII a transglutaminase in the dermal dendrocytes associated with an increased level of mast cell degranulation. Ultrastructurally, AHAs-treated photo-aged skin samples show a decreased number of desmosomes and thus results in an accumulation of tonofilaments and opening of intercellular spaces of kerationocytes, while no appreciable changes are observed in the melanocytes. In vitro studies revealed that AHAs could induce an increased degree of fibroblast proliferation and collagen production, while they may also suppress tyrosinase activity in human melanoma cell line. Recently, AHAs are becoming one of the unique rejuvenating agents in Japan. Dermatologists have to establish more effective and safer protocols in order to widely use AHAs and also further verify the action mechanisms of AHAs, utilizing image, biochemical and molecular biological analyses.