4-N-butylresorcinol has been approved in Japan, where it is used to treat melasma. This compound decreases PIH following laser therapy in melasma patients.
Aloesin a low-molecular-weight ingredient of latex exudates and glycoproteins from aloe vera gel. Aloesin is a hydroxychromone that inhibits tyrosinase at non-toxic concentrations. In vivo, aloesin inhibits UV-induced melanogenesis (13,14).
NON-PHENOLIC AGENTS Azelaic Acid
Azelaic acid is a 9-carbon dicarboxylic acid used in melasma and PIH. Azelaic acid is often better tolerated in individuals sensitive to hydroquinone. Although its lightening effects are mild, several large studies done with a diverse ethnic background population have compared its efficacy to that of hydroquinone. This has led to the conclusion that although skin irritation is greater, the efficacy of azelaic acid is similar to that of hydroquinone (15-18).
Kojic acid is a fungal metabolic product used for the treatment of hyperpigmentation. Kojic acid has been used as an agent to treat melasma (19). When combined with hydroquinone, kojic acid improves the melasma outcome treatment (20). Studies comparing the product to hydroquinone shows kojic acid has the same efficacy (21).