Melasma generally occurs when estrogen and/or progesterone stimulate pigmentation hormones, causing dark brown or grey, irregular sized patches on the face. The condition, also called chloasma or the mask of pregnancy, occurs most frequently in darker skinned women, but can also occur in lighter-skinned people of both sexes.

Melasma is primarily seen among women who are pregnant, taking birth control pills or using hormone replacement therapy. In general, the patches on the skin appear over time, and at first may resemble small moles. The patches are located on the cheeks, forehead and nose, and their irregularity in shape indicates the condition. When a pregnancy ends or hormone treatment is discontinued, the patches usually disappear in a few months.

Though women with darker skin are primarily predisposed to the condition, others may also be prone to melasma. Genetic predisposition may make one more susceptible to melasma, and dysfunction of the thyroid may also increase susceptibility. Allergic reactions to medication or cosmetics, and in some cases stress, can produce the condition. Although commonly thought of as a "woman's" disease, melasma is sometimes found in men, particularly of Central American or Latin origin. The primary indicators in men are ancestry, exposure to sunlight, and family history.

Under a Wood lamp, melasma is easily diagnosed. The lamp makes it possible to see excess melanin in the skin and distinguish it from regular skin cells. Physicians may not need the Wood lamp for diagnosis, particularly if the patient is pregnant or taking estrogen or progesterone supplements. If the patient is not pregnant or taking hormones, more careful examination, including blood tests, may be made to rule out lupus, which can cause a "butterfly" mask over the nose, forehead and cheeks.

Besides the marks on the face, melasma does not cause any other physical conditions, and the condition generally resolves on its own without treatment. However, hydroquinone, a skin cream available by prescription or over the counter, has skin bleaching properties which can reduce the appearance of melasma. Another skin lotion, Tretinoin or Retin-A, increases the skin's acidity so new skin cells develop more quickly. This treatment cannot be used during pregnancy as it is deemed unsafe to the fetus.

Other treatments for melasma, including facial peels and laser surgery, are generally considered an option for people with persistent forms of the condition. In no case will the patches resolve immediately. All treatments produce gradual results.

Anyone with melasma should exercise particular caution outside. Sun exposure can worsen the condition, and when combined with medications like Tretinoin, can further dry the skin. Limited exposure to the sun is recommended, but if sun exposure is unavoidable, sunscreen that blocks both UVA and UVB rays should be worn at all times.