Azelaic acid (AZA) is a naturally occurring saturated nine-carbon dicarboxylic acid (COOH (CH2)7-COOH). It possesses a variety of biological actions both in vitro and in vivo. Interest in the biological activity of AZA arose originally out of studies of skin surface lipids and the pathogenesis of hypochromia in pityriasis versicolor infection. Later, it was shown that Pityrosporum can oxidize unsaturated fatty acids to C8-C12 dicarboxylic acids that are cornpetitive inhibitors of tyrosinase in vitro. Azelaic acid was chosen for further investigation and development of a new topical drug for treating hyperpigmentary disorders for the following reasons: it possesses a middle-range of antityrosinase activity, is inexpensive, and more soluble to be incorporated into a base cream than other dicarboxylic acids. Azelaic acid is another option for the topical treatment of mild to moderate inflammatory acne vulgaris. It offers effectiveness similar to that of other agents without the systemic side effects of oral antibiotics or the allergic sensitization of topical benzoyl peroxide and with less irritation than tretinoin. Azelaic acid is less expensive than certain other prescription acne preparations, but it is much more expensive than nonprescription benzoyl peroxide preparations. Whether it is safe and effective when used in combination with other agents is not known.