The blisters behind the sun are considered to be solar dermatitis, polymorphic sun rash, summer dermatitis and so on. 1. solar dermatitis: acute sunburn, is the skin overexposure to ultraviolet radiation produces a kind of inflammatory reaction, ultraviolet radiation will make the human body dermis cells release inflammatory mediators, will lead to local vasodilatation, permeability increase, in the sun within a few hours to more than ten hours after the acute sunburn. 2. polymorphic sun rash: this is a sun-induced and delayed photosensitive skin disease, this disease in the hours after sun exposure without symptoms of lesions, after a few days before the appearance of lesions, lesions are often pimples, pimples or edematous erythema. 3. summer dermatitis: a long period of high temperature, high humidity will trigger summer dermatitis, the onset of the initial stage is usually dense pinpoint-sized pimples, with the development of the disease will appear pimples, there is obvious itching. Blisters behind the sun should promptly seek medical attention to clarify the cause of symptomatic treatment. You should pay attention to keep the skin clean and hygienic, do not scratch with your hands, do not contact with pollutants, to avoid infection.