Azelaic acid is a naturally occurring, nonphenolic, saturated, nine-carbon dicarboxylic acid that competitively inhibits tyrosinase. Azelaic acid was initially developed as a topical anti-acne agent but because of its effect on tyrosinase, it has also been used to treat hyperpigmentary disorders like melasma. Its mechanisms of action include the inhibition of DNA synthesis and mitochondrial enzymes, thereby inducing direct cytotoxic effects toward the melanocyte.[18] Topical azelaic acid has no depigmentation effect on normally pigmented skin; this specificity may be attributed to its selective effects on abnormal melanocytes.[19] It can be used for postinflammatory hyperpigmentation in acne. Free radicals are believed to contribute to hyperpigmentation, and azelaic acid acts by reducing free radical production.[20]