What causes blisters on the penis?

Penile blisters may result from prolonged friction due to wearing tight underwear, which damages the epidermal tissue and leads to blister formation. It is also possible that the blisters are caused by an allergic reaction to the material of the underwear or other substances. If there is a history of unhygienic sexual activity, poor local hygiene, or contact with clothing used by someone carrying the herpes virus, the blisters could also be due to infection with the herpes simplex virus, leading to genital herpes.