Melasma (previously known as chloasma) is an acquired disorder of hyperpigmentation, typically affecting sun-exposed areas of the face in the third and fourth decades of life. The condition is more common in individuals with darker skin phototypes. Melasma rarely occurs before puberty, with onset most often in the reproductive years, and it is much more prevalent in women than men.

Melasma is characterized by irregularly bordered, evenly pigmented, tan macules on the face. It often has a bilateral (and usually symmetric) distribution. Less commonly, melasma can be found on nonfacial sites.

Although the pathophysiology of melasma is poorly understood, contributing factors include ultraviolet (UV) radiation / sun exposure, visible light exposure, high estrogen states (eg, pregnancy, contraceptive use, hormone replacement therapy), genetic predisposition, family history of melasma, and certain medications (such as antiepileptic, antipsychotic, antimalarial, and antineoplastic medications). The most important environmental contributing factor is sun exposure.