Melasma (also known as chloasma faciei, or the mask of pregnancy when present in pregnant women) is a tan or dark skin discoloration. Melasma is thought to be caused by sun exposure, genetic predisposition, hormone changes, and skin irritation.

Diagnosis:

Dermatologists find most cases of melasma easy to diagnose during a visual examination. However, since melasma can resemble other skin conditions, a dermatologist may take a small biopsy during the initial visit. ... A doctor may also use a device called a Wood's light to look more closely at the skin.