6- Azelaic acid:
Azelaic acid is a naturally occurring straight chain, saturated dicarboxylic acid which is produced by yeast, Pityrosporum ovale. Azelaic acid is a rather weak competitive inhibitor of tyrosinase. In addition, it has an antiproliferative and cytotoxic effect on melanocytes (Pravez et al., 2007). Although azelaic acid was initially prescribed for the treatment of acne, it has been successfully used in the treatment of lentigines, rosacea, melasma and post inflammatory hyperpigmentation (Policarpio and Lue, 2009). Azelaic acid is not able to induce depigmentation on normally pigmented skin, suggesting its selective antiproliferative and cytotoxic action on abnormal melanocytes. It has been reported to be effective in hypermelanosis caused by physical and chemical agents, as well as other skin disorders characterized by abnormal proliferation of melanocytes. The only problem of treatment with azelaic acid is that its therapeutic response is rather slow (Solano et al., 2006)