Rectal bleeding may occur for many reasons. Common causes of rectal bleeding include:

• Anal fissure (a small tear in the lining of the anal canal)
• Constipation — which can be chronic and last for weeks or longer.
• Hard stools
• Hemorrhoids (swollen and inflamed veins in your anus or rectum)

Less common causes of rectal bleeding include:

• Anal cancer
• Angiodysplasia (abnormalities in the blood vessels near the intestines)
• Colon cancer — cancer that starts in the part of the large intestine called the colon.
• Colon polyps
• Crohn's disease — which causes tissues in the digestive tract to become inflamed.
• Diarrhea
• Diverticulosis (a bulging pouch that forms on the wall of the intestine)
• Inflammatory bowel disease (IBD)
• Ischemic colitis (colon inflammation caused by reduced blood flow)
• Proctitis (inflammation of the lining of the rectum)
• Pseudomembranous colitis (colon inflammation caused by an infection)
• Radiation therapy
• Rectal cancer
• Solitary rectal ulcer syndrome (ulcer of the rectum)
• Ulcerative colitis — a disease that causes ulcers and swelling called inflammation in the lining of the large intestine.

Call 911 or emergency medical assistance

Seek emergency help if you have significant rectal bleeding and any signs of shock:

• Rapid, shallow breathing
• Dizziness or lightheadedness after standing up
• Blurred vision
• Fainting
• Confusion
• Nausea
• Cold, clammy, pale skin
• Low urine output

Seek immediate medical attention

Have someone drive you to an emergency room if rectal bleeding is:

• Continuous or heavy
• Accompanied by severe abdominal pain or cramping

Schedule a doctor's visit

Make an appointment to see your doctor if you have rectal bleeding that lasts more than a day or two, or earlier if the bleeding worries you.