azelaic acid /az″ĕ-la′ik/ , a dicarboxylic acid occurring in whole grains and animal products. It has antibacterial effects on both aerobic and anaerobic organisms, particularly Propionibacterium acnes and Staphylococcus epidermidis; normalizes keratinization; and has a cytotoxic effect on malignant or hyperactive melanocytes. It is applied topically in the treatment of acne vulgaris.