Possible causes of acne in the sun include solar dermatitis, ultraviolet allergy, and insufficient skin cleansing. 1. Solar skin: is the skin to receive strong light caused by an acute damage to the skin reaction, clinical manifestations of the affected skin redness, swelling, burning, pain, blisters, and flaking and other symptoms, preferably in children, women, and water surface operation. 2. Ultraviolet allergy: it is an abnormal perverse reaction of the skin caused by sunlight on the human body, some people can react to a small amount of exposure to ultraviolet radiation, the clinical manifestations of the face, neck, back of the hands, side of the body and other easy to expose parts of the rash, doughnuts, or blister-like skin rash. 3. Insufficient skin cleansing: part of the population belongs to oily skin, the skin in the light of the situation of easy sweating and secretion of oil, if the cleaning is not in place will produce an accumulation of oil, clogging the pores, resulting in hair follicles are susceptible to bacterial infections and inflammation, the formation of pustules. There may be other reasons for acne in the sun, so it is recommended to go to the hospital if necessary to clarify the cause and follow the doctor’s instructions for standardized treatment.