A foreskin ulcer is a defect formed when the foreskin of the penis becomes necrotic and falls off, and is a common manifestation of sexually transmitted diseases. The ulcers on the foreskin are commonly caused by genital infections, such as genital herpes, syphilis, glans penis and, in a few cases, cancerous ulcers. The most common causes of foreskin ulcers are syphilis, hard chancre and soft chancre. The ulcers of hard chancre are round or oval in shape, with clear boundaries, edema and elevation at the periphery, flesh-red base, cartilage-like hardness when touched, and plasma secretions on the surface; the ulcers of soft chancre are similar in shape to hard chancre, but with obvious pain and softer texture. The most common disease causing foreskin ulcers is genital herpes virus infection, in which there are clusters or scattered small blisters on the foreskin, which break down to form erosions or ulcers, accompanied by pain. In addition, certain precancerous lesions can also cause foreskin ulcers, such as white keratosis and erythema hyperplasia, but they are relatively rare. To sum up, the main causes of foreskin ulcers are genital herpes, syphilis, and certain cancerous ulcers. Once you find a foreskin ulcer, you need to go to the urology department or dermatology department in time to make a clear diagnosis and then make targeted treatment.