A circle of redness and swelling of the foreskin after intercourse may be related to local excessive friction, or local contact allergy or some sexually transmitted diseases, such as gonococcal or mycoplasma infections, etc. It is recommended to go to the hospital for examination to clarify the specific causes of the disease. 1. Localized excessive friction: too much time in the same room, or too much violence and other reasons, can lead to localized redness and swelling of the foreskin, most often in the process of the first time to have sex, but also may be too high with the frequency of sexual life. 2. Local contact allergy: some patients may have contact allergy after using condoms, local redness and swelling, which may be accompanied by local itching or skin erosion. 3. Sexually transmitted diseases: patients may be infected with gonococcus or mycoplasma, chlamydia, etc. after unclean sexual contact, resulting in local redness, swelling or increased secretion, accompanied by pus in the urethra, urinary frequency and other symptoms. It is recommended to carry out relevant pathogenetic testing and so on to clarify the specific causes of the disease. There are many reasons for the redness and swelling of the foreskin after intercourse, so it is recommended to go to the hospital for consultation and examination, and active treatment.