The most common causes of bleeding after a bowel movement are hemorrhoids or anal fissures, but colorectal polyps or colorectal cancer may also be present. It is recommended to go to the Department of Anorectal Surgery for further examination and diagnosis. 1. Hemorrhoids: Hemorrhoids are varicose veins near the anus that bleed when the stool is too hard and causes the vein tumor to rupture. 2. Anal fissure: because of external forces, stool is too hard to cause the mucous membrane of the anal opening fissure, in addition to blood, will be accompanied by pain. 3. Colorectal polyps: mostly benign, may bleed when the polyp is large, the bleeding is small, the bleeding may be blood clots or darker colored blood. 4. Colorectal cancer: It may be accompanied by loss of appetite, weight loss, gradual thinning of stools, then severe constipation, and later diarrhea. Usually the duration of the disease is more than one year, and in most cases it is several years. Bleeding is caused by feces rubbing against the tumor, causing it to bleed.