Possible causes of blood in stool include gastroenteritis, anal fissures, hemorrhoids, inflammatory bowel disease, and more. Treatment can depend on the underlying cause.

This article explains the possible causes of bloody stool, including those more common in children, and how doctors diagnose and treat these issues.

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An injury to the gastrointestinal (GI) tract, inflammation, and ulcers can all cause the lining of the digestive tract to bleed. In some cases, perforation may occur, resulting in bleeding, abdominal pain, and severe illness.

If bleeding occurs in the GI tract, the blood passes out of the body with the stool.

Specific health issues that can lead to bleeding include the following:


Gastroenteritis refers to viral, fungal, or parasitic infections that affect the stomach and intestines.

Symptoms can last up to 14 days, depending on the cause, and can include:

Infection usually results from:

  • consuming food and water from contaminated sources
  • improper hand hygiene
  • contact with people who have an infection
  • consuming spoiled food, resulting in food poisoning

Some people may call viral gastroenteritis stomach flu. However, doctors no longer use this term as this is a gastrointestinal disease, while flu is a respiratory disease.

Anal fissure

Anal fissures are small tears in the lining of the anus. They may bleed and cause pain during a bowel movement.

Possible causes include:


Hemorrhoids are veins in the lower rectum and anus. Everyone has these veins, but straining or passing hard stool can cause swelling and rupturing, which can lead to symptoms such as blood in stool.

People with hemorrhoid trauma may notice a few drops of blood on the stool, on tissue, or in the toilet bowl. Factors that increase the size of hemorrhoids and, therefore, the risk of hemorrhoids bleeding include:

  • constipation
  • diarrhea
  • straining on the toilet
  • pregnancy

People may also cause bleeding by wiping too aggressively and causing trauma to large hemorrhoids. However, some people with large hemorrhoids may not have symptoms.

Peptic ulcers

Peptic ulcers are open sores that develop in the stomach lining or duodenum. A peptic ulcer on a blood vessel may cause bleeding and bloody stools.

Other symptoms include:

These ulcers can result from infection with Helicobacter pylori bacteria or long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs).


Diverticula are small pockets that can form inside the colon. They can bleed due to rupture of a vessel on the edge of the diverticulum. Healthcare professionals call this a diverticular bleed.

Risk factors for diverticular bleeding include:

  • NSAIDs
  • older age
  • blood thinners
  • cardiovascular disease
  • diabetes

Inflammatory bowel disease

Inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis, can cause bloody stool and other symptoms, such as:

  • abdominal pain
  • diarrhea
  • weight loss
  • fatigue

Experts do not know what causes IBD, but genetic factors and environmental triggers to the immune system may play a role.

Anal fistula

An anal fistula is a small tunnel that forms between the end of the bowel and the skin near the anus. Fistulas can also start in the colon and lead to another organ or the skin’s surface.

Colonic fistulas are less common than anal fistulas. Fistulas can occur as a complication of:

After an infection, pus can collect in tissues surrounding the anus. As the pus drains, it leaves behind the fistula, which may continue to ooze pus or blood.

Symptoms include:

  • skin irritation around the anus
  • pain
  • smelly discharge from anus
  • stool or gas passing through the skin, vagina, or urinary tract instead of the anus


A person may experience GI bleeding as a side effect of blood-thinning medications, such as:

Anyone who takes a blood-thinning medication and has a bloody bowel movement should notify their doctor immediately.


Cancerous tumors of the GI tract can weaken the lining of the GI tissues, causing bleeding.

However, cancer may be present without any visible signs of bleeding. People with a higher risk of cancer in the digestive system can ask a doctor about colonoscopies for surveillance, depending on their risk factors.

Doctors may recommend screening tests such as a fecal occult blood test for people without an increased risk.

Some potential causes of bloody stools in infants include:

  • Food allergies: Allergies to proteins in food or milk can cause gastroenteritis that leads to intestinal bleeding.
  • Structural changes: Issues that cause the intestines to become twisted — such as intestinal malrotation and volvulus — may lead to bleeding.
  • Necrotizing enterocolitis: This severe disease causes inflammation and tissue death within the large intestine. It usually affects premature or newborn babies. The disease can cause:
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Blood in stool may result from bleeding in the upper or lower GI tract — and the color of the blood can help indicate its source.

Black, tarry stool

Black, tarry stool may indicate a bleed in the upper GI tract, which includes the:

  • mouth
  • esophagus
  • stomach
  • duodenum — the upper part of the small intestine

As a general rule, the darker the blood, the higher the source of the bleed.

According to the American College of Surgeons, upper GI bleeding is more common than lower GI bleeding, accounting for about 70% of all GI bleeds.

Bright red blood

This can indicate a bleed in the lower GI tract or, in more severe cases, a very aggressive bleed in the upper GI tract. This section consists of:

  • large intestine
  • rectum
  • anus

No change in color

Sometimes, blood in the stool only shows up in a lab test. It is not visible in the stool. People with a family history of bowel cancer may benefit from surveillance.

A doctor may ask:

  • how much blood was visible
  • whether it was only on the toilet paper or in the bowel movement
  • how often the blood appeared
  • if there was any pain or other symptoms

They may examine the rectum and order tests to help identify the cause and check how much blood the person has lost. The next steps depend on how much blood was lost.

Emergency situations

If a person reports significant blood loss, a doctor will give them blood to stabilize them. They may order a CT scan to locate the source of the bleeding. This shows them where to target treatment.

If the doctor already knows or highly suspects the source of bleeding, they may perform an endoscopy without a CT scan.

This involves inserting a thin, flexible tube with a camera at one end into the upper or lower end of the GI tract, depending on the type of blood the person has seen.

An upper endoscopy involves guiding the endoscope through the mouth and down into the upper GI tract. A colonoscopy is a form of endoscopy that involves inserting the endoscope into the anus and through the lower GI tract.

Once the doctor identifies the source of the bleeding, they can insert tiny instruments through the endoscope and use them to repair the damaged tissue.

They may also recommend interventional radiology — image-guided procedures — to block the bleeding vessel if they cannot reach or control the source of bleeding but they can target the source with imaging.

Alternatively, if the doctor cannot resolve the bleed, they may recommend surgical removal of all or part of the damaged area.

Nonemergency situations

If the bleeding does not appear to be life threatening, the doctor may order or perform the following:

  • Complete blood count: This blood test can help determine the extent of blood loss.
  • Digital rectal examination: This involves examining the rectum manually to identify hemorrhoids or other causes of bleeding within the rectum.
  • Endoscopy: This procedure allows the doctor to view the inner lining of the GI tract.

The best treatment depends on the cause and source of the bleeding within the GI tract.

If bleeding results from an ulcer, infection, or inflammation, the doctor may prescribe medications. If cancer is present, they will recommend a suitable course of treatment, depending on the stage and other factors.

In some cases, surgery is necessary to prevent further bleeding. Methods may involve:

  • injecting medicines to stop the bleeding
  • cauterizing the site using a heat probe, electric current, or laser
  • closing off the affected blood vessels using a band or clip

Doctors may use Hemospray — a medication that helps blood to clot — to stop bleeding.

A person should seek medical attention as soon as possible if they notice black or dark red stool or have bloody diarrhea.

A person with the following symptoms may be losing a large amount of blood and should seek emergency medical help:

  • a lot of blood or clots in the toilet bowl
  • a large amount of red or dark blood in a bowel movement
  • dizziness
  • chest pain
  • extreme fatigue
  • a pale appearance
  • a rapid heartbeat
  • shortness of breath

Some symptoms are less severe but still warrant investigation. A person should see a doctor if they experience:

  • unexplained abdominal pain
  • unexplained weight loss
  • pain when passing stool
  • a small amount of blood in a bowel movement

Below are some questions people often ask about blood in the stool.

Is blood in stools serious?

Blood in stool is often a sign of hemorrhoids or piles in younger adults. However, it can also indicate a more serious condition, such as bowel cancer or internal bleeding.

People with aggressive bleeding or other severe symptoms should seek immediate medical help. Even if bleeding is not aggressive, people should speak with a doctor to identify the underlying cause.

People with a family history of bowel cancer should ask about surveillance.

When should someone worry about blood in stools?

People should see a doctor urgently if their stools are black or dark red or if they have bloody diarrhea.

Non-stop bleeding is a medical emergency. A person should call 911 or go to the emergency room if there is a lot of blood or if they are bleeding non-stop.

Blood in the stool may turn out to be nothing alarming but it is always best to discuss it with a healthcare professional. They can help determine whether or not further testing is necessary.

A person should seek emergency medical care if there is a lot of blood, if there are blood clots, or if they have other signs of blood loss, such as dizziness or fainting.

Treatment will depend on the underlying cause. A diagnosis may involve a physical exam, blood tests, or medical imaging.