Melasma is an acquired disorder of hyperpigmentation typically affecting sun-exposed areas of the face. The condition is more common in women with darker skin phototypes (including those of Hispanic and Asian descent). Melasma rarely occurs before puberty, with onset most often in the reproductive years. It has also been rarely reported in males.

Melasma is characterized by irregularly bordered, evenly pigmented tan macules on the face. Darker macules may sometimes be seen ("dermal melasma"). Although the pathophysiology of melasma is poorly understood, thyroid autoimmunity, ultraviolet radiation, hyperestrogenism (pregnancy, contraception), genetics, and anti-epileptic medications are known to be contributing factors.