A blister outside the scrotum may be caused by physiological reasons, scrotal eczema, genital herpes and other reasons. 1. Physiological reasons: If the underwear is worn tightly, it is easy to cause friction, which may lead to the proliferation of local skin tissues in the scrotum, appearing outside the scrotum grows a blister. 2. Scrotal eczema: the scrotum area is easily moist, airtight, if you do not pay attention to the private hygiene, it will be easy to form eczema, the surface will have raised small blisters, and also accompanied by itching symptoms. 3. Genital herpes: a blister outside the scrotum may also be caused by genital herpes, which is a sexually transmitted disease, most of which are caused by bad sex. Due to the infection of herpes virus, gathering-like blisters are formed on the surface of the scrotum, accompanied by itching symptoms. After a blister outside the scrotum to rule out physiological causes, the patient should promptly go to the regular hospital to consult, clarify the cause of the disease and follow the doctor’s instructions for treatment.