HYDROXY ACIDS

Hydroxy acids are present in over-the-counter and prescription formulations (Table 5). Alpha – hydroxy acids, such as glycolic acid and lactic acid, are water-soluble, and therefore penetrate to the dermis. Glycolic and lactic acids are derived from sugar cane and sour milk, respectively. Beta-hydroxy acids, such as salicylic acid, are lipid-soluble, and penetrate into the upper epidermis and into the pilosebaceous unit. Salicylic acid is derived from willow bark, wintergreen leaves, and sweet birch, and is also available in synthetic forms (54,55). Both alpha – and beta-hydroxy acids decrease cohesion among the keratinocytes in the stratum corneum, causing exfoliation (56,57). Due to their ability to penetrate the pilosebaceous unit, beta-hydroxy acids such as salicylic acid have a stronger comedolytic effect than alpha – hydroxy acids (58). However, in comparison with tretinoin and isotretinoin, salicylic acid is a mild comedolytic agent. Salicylic acid is available in both over-the-counter and prescription preparations ranging from 0.5 to 5% (59). Over-the-counter products are listed in Table 6.