Chloasma

Nature

Melasma (also known as chloasma faciei,: 854  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. Although it can affect anyone, it is particularly common in women, especially pregnant women and those who are taking oral or patch contraceptives or hormone replacement therapy medications.

Source: Wikipedia

Type 
(G) Very specific problems