What causes melasma?
No one is really certain exactly what causes melasma. Once melasma is triggered, it typically shows up as dark brown or gray patches, which are due to the body producing too much melanin, a natural substance that gives color to our hair, skin and eyes. If your body makes too much melanin, your skin gets darker. When you have melasma, that skin darkening usually appears on the face.
There are many factors that can trigger melasma, including pregnancy, birth control pills, hormone therapy, cosmetics, drugs that make the skin more susceptible to light damage, and anti-seizure medications. Because melasma is so common during pregnancy, it is sometimes referred to as "the mask of pregnancy."
Sun exposure is also a major melasma trigger because ultraviolet (UV) light from the sun can increase melanin production.