Vitiligo is a direct result of melanin loss in the skin. And there is a correlation between melanin production and UV rays. So ultraviolet light is good or bad for vitiligo patients? The absorption of UV light by the human body can cause complex biological effects, but the mechanism is not well understood. Possible biological effects caused by UV absorption in the skin are promotion and pigment formation, enhancement of the skin barrier, formation of vitamin D, affect skin immune function, cause skin erythema reaction, inhibit DNA synthesis, promote blood circulation and other effects. Clinical application of its biological effects to treat a variety of diseases, and can be enhanced by applying drugs to increase the amount of skin absorption of ultraviolet light. UV light with wavelength 300-400nm has a strong effect on melanin formation in the skin. However, the duality of things determines the advantages and disadvantages of its action. The strong ultraviolet radiation may be one of the factors that induce or aggravate vitiligo. Although the mechanism of UV induced or aggravated vitiligo potential needs further study and research, but the destructive effect of UV on melanocytes should cause vitiligo patients and doctors to be sufficiently alert.