9 Causes of Blood in Stool

2. Ulcerative Colitis

Ulcerative colitis is a type of inflammatory bowel disease that affects the large intestine, mainly the colon and rectum. It occurs when the lining of the colon becomes swollen and develops small open sores called ulcers. The exact cause is not fully understood.

The immune system may mistakenly react to the lining of the large intestine, leading to ongoing inflammation. Genetics and certain environmental factors may increase risk. Stress and diet do not cause ulcerative colitis, but they can worsen symptoms. Common symptoms include bloody stool, mucus in the stool, and an urgent need to use the bathroom.

Many people also experience cramping or pain in the lower abdomen. Symptoms often develop gradually and may flare up for weeks before easing. As inflammation progresses, the colon may lose its ability to absorb water properly, which can lead to fluid loss and fatigue. In severe cases, ulcers may cause heavy bleeding.

3. Broken Skin

Broken skin around the anus can lead to small amounts of blood appearing in the stool or on toilet paper. This often happens when tiny tears form in the lining of the anal area, known as anal fissures, usually after passing large or hard stools.

Straining during bowel movements, frequent wiping, irritation from diarrhea, or dryness and low moisture around the anus can all make the skin more likely to crack and bleed. Common symptoms include sharp pain during or after a bowel movement. The blood is typically bright red and appears separate from the stool rather than mixed within it.

Bleeding is usually mild but can be uncomfortable. To support healing, keep the area clean and avoid harsh wiping. Drinking enough water and adding fiber to your diet can help soften stools and reduce strain.

4. Diverticular Disease

Diverticular disease occurs when small pouches, called diverticula, form in the wall of the large intestine. These pouches can trap waste or become irritated, and when they bleed, you may notice bright red or maroon blood in your stool. The bleeding is often painless, though it can be heavy in some cases.

Diverticula usually develop because of increased pressure inside the colon. A diet low in fiber can make stools hard and dry, causing the colon to strain more to move them. Over time, this pressure may create weak spots in the bowel wall, leading to pouch formation. In some cases, the pouches become inflamed or infected, a condition known as diverticulitis.

This may cause abdominal pain, fever, or changes in bowel habits. If a blood vessel near one of the pouches becomes damaged, bleeding can occur and may require medical attention.

5. Angiodysplasia

Angiodysplasia occurs when small blood vessels in the colon or small intestine become enlarged and fragile, allowing blood to leak into the digestive tract. It most often affects the right side of the colon and becomes more common with age.

Many people do not feel pain with angiodysplasia. Some notice bright red or dark blood in the stool, while others only learn about the condition through stool testing. Bleeding may happen off and on and can be easy to miss. When bleeding continues over time, even in small amounts, it can lead to anemia.

This may cause symptoms such as fatigue, shortness of breath, or pale skin as the body loses red blood cells. Angiodysplasia is identified using tests such as colonoscopy or CT angiography, along with blood tests that check for signs of anemia. These tests help locate the bleeding vessels and assess the extent of blood loss.

6. Cancer

Cancer in the digestive system, such as colon, rectal, or stomach cancer, can sometimes cause blood to appear in the stool. Bleeding may occur when a tumor damages nearby blood vessels or tissues. Depending on where the bleeding starts, the blood may appear red, dark red, or make stools look black.

Along with bleeding, other changes may develop over time. These can include ongoing diarrhea or constipation, stools that appear narrower than usual, or a sensation that the bowel does not fully empty. Some people also experience abdominal pain, persistent fatigue, or unintended weight loss.

To identify the source of bleeding, tests such as stool studies or a colonoscopy may be used to find abnormal growths or areas of concern. In some cases, a small tissue sample is collected to confirm the diagnosis. Treatment options vary and may include surgery, chemotherapy, radiation therapy, or other targeted approaches designed to slow or stop cancer growth.

7. Polyps

Polyps are small growths that form on the inner wall of the colon or rectum. They develop when cells in the lining grow more than they should. Most polyps are harmless, but some can slowly turn into cancer over time if not removed.

Polyps can appear as a single growth or in clusters. They become more common with age, especially after 50. A family history of colon cancer or having polyps in the past can also increase risk. Some grow on thin stalks and resemble small mushrooms, while others are flat and attach directly to the bowel wall.

Their size can range from a few millimeters to several centimeters. Many people with polyps do not have noticeable symptoms. When polyps bleed, you may see red or dark blood in the stool or on toilet paper after a bowel movement. In some cases, bleeding is not visible and is only detected through stool testing.

8. Varicose Veins of the Esophagus

Varicose veins of the esophagus, also called esophageal varices, develop when blood flow through the liver slows due to scarring or damage. As pressure builds in nearby veins, the veins leading to the esophagus become swollen and stretched. These enlarged veins are fragile and can tear or burst, leading to bleeding that may show up in the stool.

This condition most often occurs in people with long-term liver disease, such as cirrhosis. Ongoing liver damage increases pressure in the portal vein system, raising the risk of varices and bleeding. Avoiding alcohol and managing liver-related conditions may help lower future risk. Many people do not notice symptoms until bleeding occurs.

Small amounts of bleeding can make stool appear dark or tar-like. Heavier bleeding may cause vomiting blood, dizziness, or weakness due to blood loss. Evaluation typically involves using a thin tube with a camera, called an endoscope, to look for enlarged veins and active bleeding.

9. Peptic Ulcers

Peptic ulcers are open sores that form in the inner lining of the stomach or the upper part of the small intestine. They develop when the protective layer that normally shields the digestive lining from stomach acid becomes damaged, allowing acid to irritate the tissue and cause pain or bleeding.

The most common causes include infection with a specific type of bacteria and frequent use of nonsteroidal anti-inflammatory drugs. These factors weaken the stomach’s protective defenses and increase the risk of ulcer formation. Stress and spicy foods do not directly cause ulcers, but they can worsen symptoms. Typical symptoms include a dull or burning pain in the upper abdomen, bloating, nausea, or feeling full quickly.

The pain often comes and goes and may feel worse when the stomach is empty. If an ulcer bleeds, you may notice black or tarry stools. In some cases, blood may appear dark red or mixed with stool. Severe bleeding can cause vomiting that looks like coffee grounds, which suggests bleeding higher in the digestive tract.