Melasma  which is also called  the mask of pregnancy or cholasma is both sun-exposed and 

hormone related and usually appears as a tan or dark discoloration on the face of pregnant women

or women taking birth control or hormone replacement therapy. Current thought is that the female

hormones estrogen and progesterone stimulate the skin melanocytes to produce more pigment

called melanin.

            In addition,melasma seems to be more prevalent in women living in areas with intense sun

exposure. Unusual causes of melasma include allergic reactions to medications and cosmetics.

          The good news about melasma is that the discoloration usually diasppears on its own several

months after giving birth or stopping oral contraceptives or hormone replacement therapy. The bad

news is that even after these events it usually returns with continual exposure to the sun.

          Treatment also includes topical (applied directly to the skin) depigmenting agents such as

hydroquinone,tretinoin and azelaic acid as well as the use of broad spectrum sunscreens and avoidance 

of other precipitants such as hormonal triggers. 

         Also,I wonder if  lignin peroxidase which is currently being studied as a lightening agent will

have a role in the treatment of melasma.