A circle of foreskin redness after intercourse, the possible causes are as follows: 1, excessive local friction, resulting in local redness and swelling of the foreskin, mostly seen in the process of the first or early sexual intercourse, can appear corresponding changes, may be related to the length of intercourse or too high frequency. It is recommended to stop the related intercourse, can recover by itself. 2, local contact allergy, after the use of condoms may appear contact allergy, local redness and swelling, can be accompanied by local itching or skin erosion and other changes. It is recommended to go to the hospital for examination, and if contact allergy is diagnosed, anti-allergy treatment is required. 3, some sexually transmitted diseases, such as not fixed sexual partners, unclean sexual contact, may be infected with gonococcus or mycoplasma, chlamydia, etc., resulting in local redness or increased discharge, pus in the urethra, urinary frequency, urinary urgency and other symptoms. It is recommended that relevant pathogenic tests, such as culture tests for gonococcus or mycoplasma or chlamydia, be performed to confirm the diagnosis and provide symptomatic treatment.