Melasma on hands may be related to heredity, ultraviolet ray exposure, medication and diseases. 1. Heredity: Melasma has hereditary tendency, if parents suffer from melasma, the probability of children suffering from melasma will increase, which may lead to the appearance of melasma on hands. 2. Ultraviolet ray irradiation: long time outdoor work, no sun protection measures for hands, and long time exposure to sunlight may cause chloasma on hands and aggravation of chloasma. 3. Drug factors: Melasma on hands may also be related to drug factors, such as prolonged application of contraceptive pills, phenytoin sodium, chlorpromazine and other drugs, which may induce melasma-like lesions and lead to melasma on hands. 4. Disease factors: chloasma may also be secondary to certain diseases related to hormone levels, such as uterine fibroids, ovarian cysts, cirrhosis of the liver and so on. If you have chloasma on your hands, you should seek medical examination as early as possible to clarify the specific cause and carry out treatment in time.