Blood blisters on the outer skin of the scrotum may be caused by overstimulation, bacterial infection, genital herpes and other factors. 1. Overstimulation: when the scrotum is subjected to excessive pressure or excessive friction, it will cause tension blisters to appear on the outer skin of the scrotum, accompanied by pain, redness and other symptoms. 2. Bacterial infection: men do not pay attention to the hygiene of the lower body, which may lead to local bacterial infection of the scrotum, and when the infection is serious, it will cause blood blisters to appear on the outer skin of the scrotum, accompanied by itching, tingling and other symptoms, and pus will appear in serious cases. 3. genital herpes: men have unclean sex, may be infected with genital herpes, will make the scrotum as well as the penis area blood blisters, accompanied by tingling, and has a strong contagious, serious will be broken and oozing. If there are blood blisters on the outer skin of the scrotum and other abnormal manifestations, it is recommended to consult a doctor in time for appropriate examination and treatment to avoid adverse effects.