Although the causes of melasma are not completely understood, several factors are known to play a role. Clearly genetics is a factor, as women with a family history of melasma are more likely to develop the condition. Also, hormonal factors play a role, as pregnancy and birth control pills may also cause melasma. Chloasma is a term that is sometimes used to describe the melasma that occurs during pregnancy. In addition, sun exposure is one of the most important contributing factors in the development of melasma.
It is believed that melasma results from exposure to estrogen and progesterone from the blood combined with exposure to ultraviolet light from the sun. Together, these exposures result in an over-stimulation of the pigment producing cells in the skin, increased production of melanin pigment, and the characteristic brown patches of melasma.