Melasma

Melasma (also known as chloasma or the mask of pregnancy when present in pregnant women) is a tan or dark facial skin discoloration. Although it can affect anyone, melasma is particularly common in women, especially pregnant women and those who are taking oral contraceptives or hormone replacement therapy (HRT) medications. It is also prevalent in men and women of Native American descent (on the forearms) and in men and women of German/Russian Jewish descent (on the face).

See complete Wikipedia article here.

For more information from the American Academy of Dermatology click here.