Topical therapies for melasma and disorders of hyperpigmentation

Facial hyperpigmentation is usually a reflection of an increased amount of melanin either within the epidermis, the dermis, or both (mixed pattern). The increase in melanin content is due to an increased number of functioning melanocytes (melanocytosis), an increased amount of melanin production without a numerical alteration of melanocytes (melanosis), or both. Topical hypo/depigmenting agents are most effective in those disorders where the increased melanin pigment (secondary to melanocytosis or melanosis) is within the epidermis. In patients with melasma, one of the more common causes of facial hyperpigmentation, two major groups of hypo/depigmenting agents have been used: phenolic derivatives and nonphenolic compounds. Hydroquinone, a phenolic derivative, has been used most extensively. It is applied to areas of involvement, either alone or in combination with one or two of the following: tretinoin, salicylic acid, glycolic acid, or corticosteroid. Phenolic thioethers are a new class of phenolic derivatives, and they exhibit both cytocidal and cytostatic effects selectively on melanocytes. Nonphenolic depigmenting agents include azelaic acid and kojic acid. If the facial hyperpigmentation is not improved by first‐line topical therapies, chemical peels may be used in combination. The precise cause of melasma is not known, and multiple factors have been implicated. However, a genetic predisposition and exposure to ultraviolet (UV) light are very important factors. Avoidance of direct exposure to sunlight and application of broad‐spectrum sunscreens are required during and after the period of active treatment. In addition to melasma, other causes of facial hyperpigmentation include Riehl's melanosis, photocontact dermatitis, the sequelae of inflammatory diseases such as acne vulgaris and cutaneous lupus, and nevus of Ota.