The red rash on the glans is mostly caused by circumcision, allergic rashes, glansitis, sexually transmitted diseases and so on. 1. Circumcision: circumcision will lead to the presence of a large number of local bacteria, long-term chronic and easy to stimulate the glans easily cause red rash. 2. Allergic rash: after the glans comes into contact with allergens, itching, red rash and other allergic symptoms will appear. 3. Glans inflammation: glans infection with bacteria, Candida albicans, trichomonas, etc. can lead to different types of glans inflammation, which can lead to the symptoms of red rash on the glans. 4. Sexually transmitted diseases: such as genital herpes, condyloma acuminatum, syphilis, etc., early red rash on the glans can appear. Appearance of red rash on the glans need to go to the hospital in a timely manner for relevant examinations to identify the cause of the disease, targeted treatment; in addition to pay attention to private hygiene and cleanliness, to avoid unclean sex.