Skin tanning is related to external factors such as ultraviolet rays and visible light, as well as internal factors such as skin melanin. 1. External factors (1) Ultraviolet rays: There are A-band, B-band and C-band rays. B-band rays cause inflammatory reactions in the skin, leading to problems such as hyperpigmentation. However, A-segment UV rays directly darken the skin without causing skin erythema. (2) Visible light: Blue light, also known as high-energy blue light, may also darken the skin. This kind of light causes skin darkening to last longer than that caused by ultraviolet light. 2. Intrinsic factors: As melanin can affect the color of the skin, it is mostly produced by melanocytes in the basal layer of the epidermis. As ultraviolet light, visible light, etc. can affect the synthesis and transfer of melanin, thus making the skin darker. If there is a skin tanning, sunburn or whitening needs of patients are recommended to the regular hospital dermatology consultation, under the guidance of the doctor symptomatic treatment.