Hormones can play a part in melasma, although experts are still unclear on the exact link.
Increased levels of estrogen, progesterone, and melanocyte-stimulating hormone (MSH) during pregnancy may cause melasma.
However, people who have not given birth and develop melasma do not have higher levels of estrogen or MSH, but the areas of melasma do have higher levels of estrogen receptors.
Oral contraceptives containing estrogen and progesterone may also link to melasma, as well as diethylstilbestrol, which is a synthetic form of estrogen.
People who take progesterone postmenopause may develop melasma, while those who take estrogen-only medication do not. This suggests progesterone plays a key role in the formation of melasma.