What causes blood in stool

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Last updated: April 4, 2026

Quick Answer: Blood in stool, also known as hematochezia or melena, can be caused by a variety of conditions, ranging from minor issues like hemorrhoids or anal fissures to more serious problems such as inflammatory bowel disease, ulcers, or colorectal cancer. The appearance of the blood (bright red or dark and tarry) can offer clues to its origin in the digestive tract.

Key Facts

Bright red blood in stool often indicates bleeding in the lower part of the digestive tract, like the rectum or colon.
Dark, tarry, or black stools (melena) usually suggest bleeding higher up in the digestive tract, such as the stomach or small intestine.
Common benign causes include hemorrhoids, anal fissures, and diverticular disease, accounting for many cases.
More serious causes like inflammatory bowel disease (Crohn's disease, ulcerative colitis), peptic ulcers, and polyps require prompt medical attention.
Colorectal cancer is a significant concern, especially in older adults or those with a family history, and screening is crucial.

Overview

Seeing blood in your stool can be alarming, but it's a common symptom with a wide spectrum of potential causes. The color and consistency of the blood, along with other accompanying symptoms, are important diagnostic clues for healthcare professionals. It's crucial to consult a doctor to determine the exact cause and receive appropriate treatment.

What is Blood in Stool?

Blood in the stool refers to the presence of blood in the feces. The appearance can vary significantly. It might be bright red, maroon, or even appear as dark, tarry stools. This variation in appearance is often related to the location and amount of bleeding within the digestive system.

Common Causes of Blood in Stool

Many conditions can lead to blood in the stool. Some are relatively minor and easily treatable, while others require more aggressive medical intervention.

1. Hemorrhoids

Hemorrhoids are swollen veins in the anus and rectum, similar to varicose veins. They are a very common cause of bright red blood on toilet paper or in the toilet bowl after a bowel movement. They can be internal or external and may cause itching, pain, and discomfort.

2. Anal Fissures

An anal fissure is a small tear in the lining of the anus, often caused by passing large or hard stools. Like hemorrhoids, they typically cause bright red bleeding, often noticeable on toilet paper, and can be quite painful, especially during bowel movements.

3. Diverticular Disease

Diverticulosis occurs when small pouches (diverticula) form in the wall of the colon. If these pouches become inflamed (diverticulitis) or if a blood vessel within a pouch erodes, it can lead to significant bleeding. This bleeding is often painless and can range from mild to severe, sometimes resulting in maroon-colored stools.

4. Peptic Ulcers

Ulcers are sores that develop on the lining of the stomach or the upper part of the small intestine (duodenum). They can be caused by infection with Helicobacter pylori bacteria or by the long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen. Bleeding from an ulcer can cause dark, tarry stools (melena) due to the blood being digested as it passes through the digestive tract. Severe bleeding can also lead to vomiting blood.

5. Inflammatory Bowel Disease (IBD)

IBD is a group of chronic inflammatory conditions affecting the digestive tract. The two main types are Crohn's disease and ulcerative colitis. Both can cause inflammation and ulceration of the intestinal lining, leading to blood in the stool, often mixed with mucus. Diarrhea, abdominal pain, and weight loss are common symptoms.

6. Polyps and Colorectal Cancer

Colorectal polyps are small growths on the lining of the colon or rectum. While most polyps are benign, some can develop into cancer over time. Polyps can bleed, sometimes intermittently, leading to occult blood (blood not visible to the naked eye) or visible red or dark blood in the stool. Colorectal cancer itself is also a significant cause of bleeding, which may be the first sign of the disease.

7. Other Causes

Less common causes include bleeding from the upper gastrointestinal tract (esophageal varices, Mallory-Weiss tears), ischemic colitis (reduced blood flow to the colon), infections causing gastroenteritis, and certain medications that can irritate the stomach lining.

When to See a Doctor

Any instance of blood in the stool should prompt a consultation with a healthcare provider. It is particularly important to seek immediate medical attention if you experience:

Large amounts of bleeding
Sudden, severe abdominal pain
Dizziness, lightheadedness, or fainting
Vomiting blood or material that looks like coffee grounds
Black, tarry stools accompanied by fever or weakness
Unexplained weight loss

Diagnosis and Treatment

Diagnosis typically involves a thorough medical history, physical examination, and potentially further tests such as:

Fecal Occult Blood Test (FOBT): Detects hidden blood in the stool.
Colonoscopy: A procedure using a flexible camera to examine the entire colon, allowing for visualization and biopsy of abnormalities.
Sigmoidoscopy: Similar to colonoscopy but examines only the lower part of the colon.
Upper Endoscopy (EGD): Examines the esophagus, stomach, and duodenum.
Imaging Tests: Such as CT scans or barium enemas, may be used in certain situations.

Treatment depends entirely on the underlying cause. It can range from dietary changes and topical creams for hemorrhoids and fissures to medications for IBD and ulcers, or surgery for polyps, cancer, or severe bleeding.

Prevention

While not all causes of blood in the stool are preventable, maintaining a healthy diet rich in fiber, staying hydrated, regular exercise, and avoiding excessive use of NSAIDs can reduce the risk of some conditions like constipation, hemorrhoids, and diverticular disease. Regular colorectal cancer screenings are vital for early detection.