Erythema of the glans after coitus may be caused by friction stimulation, prepuce glansitis, sexual diseases, etc., and need to be further diagnosed by the doctor. 1. Friction stimulation: friction action during coitus can cause local capillary expansion, which can be manifested in a phenomenon similar to glans erythema. 2. Foreskin glansitis: due to the stimulation of inflammatory factors, can cause erythema, itching and other symptoms at the glans. 3. Sexual diseases: such as syphilis, if infected with syphilis spirochete in the process of coitus, small erythema can appear. It is recommended that those who have erythema on the glans after coitus should go to the hospital in time to clarify the cause, and if treatment is needed, standardized treatment should be carried out under the guidance of the doctor to avoid delaying the condition.