Alpha hydroxy acids (AHAs) work mainly as an exfoliant. They cause the cells of the epidermis to become "unglued" allowing the dead skin cells to slough off, making room for regrowth of new skin. AHA's may improve the appearance of wrinkles, roughness, and mottled pigmentation of photodamaged skin after months of daily application. AHA's work best in a concentration of 5% to 8% and at a pH of 3 to 4. Beta hydroxy acids (BHAs) such as salicylic acid are topical exfoliants that can reverse the appearance of the effects of photoaging such as fine wrinkles and discolored skin.