Blood in Stool (Rectal Bleeding): Causes and When to Worry

What the color of the blood tells you

Black stool is not always blood. Iron tablets, bismuth (Pepto-Bismol), black licorice and blueberries can darken stool. Beets, red food coloring and tomato skins can make it look red. Tarry, sticky, smelly black stool is the pattern that suggests bleeding. See melena for more detail.

Common causes of blood in stool

Hemorrhoids

Hemorrhoids are swollen veins inside or around the anus. Internal hemorrhoids bleed painlessly, leaving bright red blood on the paper or dripping into the bowl after a bowel movement. External hemorrhoids can form a painful lump. Constipation, straining, pregnancy and long sitting on the toilet make them worse.

Anal fissure

An anal fissure is a small tear in the lining of the anus, usually after passing a hard stool. It causes sharp pain during and after a bowel movement, often lasting an hour or more, and a little bright red blood.

Diverticular bleeding

Small pouches in the colon wall (diverticulosis) can suddenly bleed, causing a large amount of painless red or maroon blood. It is the most common cause of major lower bowel bleeding in older adults. It usually stops on its own but needs hospital assessment.

Infections

Bacterial infections such as Campylobacter, Salmonella, Shigella and some E. coli cause bloody diarrhea with cramps and fever. C. difficile infection can follow antibiotic use.

Serious causes not to miss

• Colorectal polyps and cancer: colorectal cancer may cause blood mixed with stool, a lasting change in bowel habit, anemia, weight loss or no symptoms at all. Rates are rising in adults under 50, which is why screening now starts at 45 in the US.
• Inflammatory bowel disease: ulcerative colitis causes bloody diarrhea with mucus and urgency. Crohn's disease can also bleed, often with pain and weight loss.
• Peptic ulcer: a bleeding peptic ulcer causes black stools, sometimes with upper abdominal pain. NSAIDs and H. pylori are the main causes.
• Ischemic colitis: reduced blood flow to the colon, usually in older adults, causes sudden cramping left-sided pain followed by bloody diarrhea.
• Angiodysplasia: fragile blood vessels in the bowel wall that bleed slowly or intermittently, mostly in older people.
• Intussusception: one part of the bowel telescopes into the next. In children aged 3 months to 3 years it causes episodes of severe crying with drawn-up legs and "redcurrant jelly" stool. In adults it is rare and usually caused by a polyp or tumor acting as a lead point, causing cramping pain, vomiting and sometimes blood in the stool.
• Meckel's diverticulum: a cause of painless, heavy bleeding in young children.

Accompanying symptoms and what they suggest

When to worry about blood in stool

Any visible blood should be mentioned to a doctor. The level of urgency depends on how much there is and what comes with it. Seek emergency care for heavy bleeding, black stools, or bleeding with dizziness or fainting. See a doctor within days for bleeding in anyone over 45, blood mixed into the stool, or bleeding with a change in bowel habit, weight loss or anemia.

How doctors find the cause

A doctor will ask about the color and amount of blood, when it appears, pain, bowel habits, weight, medicines (blood thinners, NSAIDs, iron), and family history. They will examine your abdomen and do a digital rectal exam, often with a short scope (anoscopy or proctoscopy) to look at the anal canal.

Tests may include:

• Blood tests: a complete blood count for anemia, iron studies, clotting tests and kidney function
• Stool tests: for infection, or a fecal immunochemical test (FIT) for hidden blood
• Colonoscopy: a camera through the whole colon, the main test for polyps, cancer, colitis and diverticular bleeding. Polyps can be removed during the test
• Flexible sigmoidoscopy: a shorter scope of the lower colon in younger people with typical rectal bleeding
• Upper endoscopy: for black stools, to look at the esophagus, stomach and duodenum
• CT angiography: for brisk bleeding, to find the bleeding vessel

Treatment

Treatment targets the cause:

• Hemorrhoids: more fiber and fluids, avoiding straining, sitz baths, over-the-counter creams, and office procedures such as rubber band ligation
• Anal fissure: fiber, stool softeners, warm baths and prescription ointments that relax the anal muscle
• Infection: fluids, and antibiotics only for some infections
• IBD: anti-inflammatory and immune-modifying medicines
• Ulcers: acid-suppressing medicines and H. pylori treatment
• Polyps and cancer: removal during colonoscopy, surgery, and other cancer treatments
• Major bleeding: hospital care with fluids, blood transfusion, and stopping the bleeding by endoscopy, interventional radiology or surgery

Home care for minor bleeding from hemorrhoids or a fissure

• Eat 25 to 35 grams of fiber a day from fruit, vegetables, whole grains or a fiber supplement, and drink plenty of water.
• Do not strain or sit on the toilet for long periods, including scrolling on a phone.
• Soak in a warm bath for 10 to 15 minutes after bowel movements.
• Use soft, unscented wipes or rinse with water.

Frequently asked questions

Should I worry about bright red blood in my stool?

A small amount of bright red blood on the paper after a hard stool is usually from hemorrhoids or a fissure. It still deserves a doctor's check, especially if you are over 45, the blood is mixed into the stool, it keeps happening, or you have weight loss or a change in bowel habit.

What does black stool mean?

Black, tarry, sticky and foul-smelling stool usually means bleeding from the stomach or upper intestine, such as a bleeding ulcer. This needs urgent medical care. Iron tablets and bismuth medicines also turn stool black, but the stool is not usually sticky or tarry.

Can stress cause blood in stool?

Stress does not directly cause bleeding. It can worsen constipation, hemorrhoids, irritable bowel symptoms and flares of inflammatory bowel disease, which can bleed. Blood in the stool should not be blamed on stress without a medical assessment.

Can intussusception cause blood in stool in adults?

Yes, but it is rare in adults. Adult intussusception is usually caused by a polyp or tumor that pulls one segment of bowel into the next. It causes cramping abdominal pain, vomiting, bloating and sometimes blood in the stool. It is diagnosed by CT scan and usually treated with surgery.

Is blood in stool always cancer?

No. Most rectal bleeding is caused by hemorrhoids or fissures. However, colorectal cancer can cause bleeding and is increasingly found in adults under 50, so new bleeding, especially with other symptoms, should be investigated rather than assumed to be hemorrhoids.

What tests are done for blood in stool?

Most people have a rectal examination and a blood count. Depending on age and symptoms, the next step is usually a colonoscopy or sigmoidoscopy. Black stools are investigated with an upper endoscopy. Stool tests check for infection or hidden blood.