Melasma. As exact cause is not known its very resistant to treatment. Hormonal changes most commonly after pregnancy, other various causes like chronic stress, lack of sleep, due to cosmetics,chronic sun exposure , heriditory causes..etc Various modalities of treatment are available Like topical medication , systemic drugs(tranaeximic acid) , chemical peels, I/L injections with tranaexmic acid,mesoroller with vitc, q switched laser..etc... but doing all this treatment recurrence rate is very high, need to be maintained for long time..always use sunscreens in morning &steriod free skin lightening agents in the night.