Picture of Melasma
Melasma, or "pregnancy mask", is a discoloration of the skin that occurs along the cheeks, nose, upper lip, forehead, and bridge of the nose due to a change in hormone level during pregnancy. The condition may also occur due to the use of birth control pills. It is imperative to use sunscreen if a woman has melasma because sun exposure further darkens the affected skin. Topical prescription medication may be applied to lighten the skin if the discoloration is bothersome.
Text Reference: American Academy of Dermatology: "Melasma"