Is Blood in Your Stool a Sign of Cancer?

This page is for anyone who has noticed blood in their stool and wonders if it could be cancer. It covers what the blood can look like, the common causes, and what a doctor checks.

Not always, but it should never be ignored. Hemorrhoids, infection and other conditions can cause it. Blood can also be a sign of colorectal cancer, so see your doctor right away to find the cause.

Blood in the stool can look different depending on where it comes from. Bright red blood often points to bleeding lower down, near the rectum or anus. Black, tarry stool can mean bleeding higher up in the digestive tract, such as the stomach. Sometimes there is no visible blood at all. Only a small, hidden amount shows up, and a stool test can detect it. This is one reason routine colorectal screening exists. It can catch bleeding you would never notice on your own.

A tumor in the colon or rectum can bleed. Slow blood loss over time can cause anemia, a low red blood cell count. The American Cancer Society says this can cause tiredness and weakness. Sometimes anemia is the first clue.

• Hemorrhoids, swollen veins in the rectum or anus, can cause bleeding.
• Anal fissures, small tears in the anus, can also bleed.
• Infections and inflammatory bowel disease can also cause blood in the stool.
• Some foods and medicines, such as black licorice, blueberries, iron pills, or bismuth (Pepto-Bismol), can turn stool black without bleeding.

Your doctor asks about the color and amount of blood. They ask whether you have pain, weight loss, or a change in bowel habits. A physical exam, including a rectal exam, can find hemorrhoids or fissures right away in many cases. If the cause is not clear, your doctor may suggest a colonoscopy. A thin, flexible tube with a camera examines the entire colon. Doctors can remove any abnormal tissue for a biopsy during the same procedure. NCI puts the usual wait for a pathology report at up to 10 days after the procedure.

Finding hemorrhoids explains bleeding for many people, but it does not automatically rule out a second cause higher up. If bleeding continues after hemorrhoids are treated, or if you are due for colorectal screening, follow up rather than assuming the hemorrhoids explain everything.

CDC notes that the U.S. Preventive Services Task Force recommends colorectal cancer screening for adults age 45 to 75, even without symptoms. A yearly stool test, called a fecal immunochemical test, can pick up hidden blood you would never notice. A colonoscopy is usually done every 10 years for people at average risk. It checks for polyps or cancer in the rectum and whole colon. Doctors can remove most polyps, small growths that can turn into cancer, during the test.

• Call 911 or go to an emergency department if you pass a large amount of blood, your stools look black and tarry, you vomit blood, or bleeding comes with dizziness, chest pain, a racing heart, or severe pain in the belly. Do not drive yourself.
• Call your care team right away if bleeding keeps repeating over several days, or you feel unusually weak or breathless with it.
• Call your doctor right away if you see any blood in your stool, even once and even when you feel well. MedlinePlus and the American Cancer Society both say to contact your doctor promptly.

• What could be causing this bleeding?
• Do I need a colonoscopy, or can we start with an exam?
• Am I due for colorectal cancer screening based on my age?
• What amount or pattern of bleeding should send me to urgent care?

• National Cancer Institute — Colon Cancer Treatment (PDQ)
• MedlinePlus — Gastrointestinal bleeding
• MedlinePlus — Black or tarry stools
• American Cancer Society — Colorectal Cancer Signs and Symptoms
• CDC — Screening for Colorectal Cancer
• National Cancer Institute — Pathology Reports