Melasma is a condition in which areas of the skin become darker than the surrounding skin. Doctors call this hyperpigmentation. It typically occurs on the face, particularly the forehead, cheeks and above the upper lip. The dark patches often appear on both sides of the face in a nearly identical pattern. The darker-colored patches of skin can be any shade, from tan to deep brown. Rarely, these dark patches may appear on other sun-exposed areas of the body.
Melasma occurs much more often in women than in men, and usually is associated with hormonal changes. That is why the dark patches develop often during pregnancy, or if a woman is taking hormone replacement therapy (HRT) or oral contraceptives. Melasma during pregnancy is relatively common. Sometimes it is called the "mask of pregnancy" or "chloasma." The dark patches typically last until the pregnancy ends.
The most important factor in the development of melasma is exposure to sunlight. Using medications that make you sensitive to the sun (photosensitizing) can increase your risk of developing melasma. These can include some cosmetics and medicines used to treat ovarian or thyroid problems. Protection from the sun is a necessary part of treatment of melasma. For example, women who are pregnant or who take a hormone medication and avoid the sun are less likely to develop melasma than are those who spend a lot of time in the sun.