As aggravating as hyperpigmentation can be, understanding why it’s
happening and how you can stop it (yes, it can be done) is rule
number-one on the path to clear, even skin.
What Causes Melasma?
The exact cause of melasma remains unknown. Experts believe that the dark patches in melasma could be triggered by several factors, including pregnancy, birth control pills, hormone replacement therapy (HRT and progesterone), family history of melasma, race, antiseizure medications, and other medications that make the skin more prone to pigmentation after exposure to ultraviolet (UV) light. Uncontrolled sunlight exposure is considered the leading cause of melasma, especially in individuals with a genetic predisposition to this condition. [source: MedicineNet.com