Blood on male underwear may be some physiological phenomenon, but also may be caused by certain disease factors such as hemorrhoids, kidney stones, urinary tract infections, etc., should be timely consultation to identify the cause of the disease. 1. Physiological phenomenon: men’s underwear with blood may be due to sexual misconduct or excessive masturbation, caused by the foreskin ligament tear or genital injuries, will lead to men’s underwear with blood, this is a normal physiological phenomenon, after recuperation can be restored to normal. 2. Pathological factors: (1) hemorrhoids: it may also be that the venous plexus at the bottom of the anorectum and the anal mucosa is varicose, thus forming bleeding caused by hemorrhoids. (2) Kidney stones: if the patient suffers from kidney stones, the stones will damage the mucous membrane of the ureter or bladder, and there will be blood on the male underwear. (3) Urinary tract infection: if the patient has urinary tract infection, it will trigger congestion and erosion of urethral mucosa, which will also trigger blood on male underwear. Other diseases such as rectal tumors can also lead to blood on male underwear, patients should consult the doctor in time, after clarifying the cause of the disease under the guidance of the doctor for treatment.