A ring of redness on the foreskin may be caused by overstimulation, phimosis, allergy and other factors. 1. Overstimulation: men frequently masturbate and masturbate with too much force, causing stimulation to the foreskin, which can lead to a circle of redness in the foreskin, accompanied by mild pain. 2. Circumcision: men do not wash the foreskin area for a long time, may induce infection, causing circumcision, stimulated by inflammatory substances, will lead to a circle of redness, accompanied by itching, swelling and other symptoms. 3. Allergy: for example, allergy to condoms, so that the foreskin localized allergic reaction, will make the foreskin has a circle redness, may also be accompanied by itching. The foreskin has a circle, and there are other abnormal manifestations, should be vigilant for disease factors, it is recommended to consult a doctor for appropriate examination and treatment, to avoid adverse effects.