It may be alarming to find blood in the toilet or after wiping. There are many possible causes, and some are relatively harmless, some require treatment, and some may warrant emergency care.

Below, learn more about the possible causes of bloody stool, including those more common in children. Also, find out how doctors diagnose and treat these issues.

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The amount of blood in stool can indicate the severity of the underlying issue.

Blood in stool may result from bleeding in the upper or lower gastrointestinal (GI) tract — and the color of the blood can help indicate its source.

Black, tarry stool

Black, tarry stool may point to a bleed in the upper GI tract. As a general rule, the darker the blood, the higher the source of the bleed.

The upper GI tract includes the mouth, esophagus, stomach, and upper part of the small intestine, called the duodenum.

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 is usually a sign of a bleed in the lower GI tract. This section consists of the large intestine, rectum, and anus.

An injury to the GI tract can cause irritation that leads to bleeding. In other cases, ulcers form, rupturing the lining of an organ. In either event, the blood passes out of the body with the stool.

Specific health issues may be involved, such as:

Gastroenteritis

Gastroenteritis is a blanket term for conditions that cause an upset stomach. Most of these cases result from a bacterial or viral infection, according to the United Kingdom’s National Health Service (NHS).

Depending on the circumstances and symptoms — which can include bloody diarrhea — a doctor may refer to the infection as food poisoning or stomach flu.

Anal fissure

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

Hemorrhoids

Hemorrhoids are swollen veins in the lower rectum. Straining or passing hard stool can rupture these veins, leading to bloody bowel movements.

Peptic ulcers

Peptic ulcers are open sores that develop in the lining of the stomach or duodenum.

A peptic ulcer that forms on a blood vessel may cause bleeding and bloody stools.

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

Diverticula

Diverticula are small pockets that can form inside the colon. They are prone to infection and inflammation and can sometimes rupture and bleed.

The medical term for infection and inflammation of diverticula is diverticulitis.

Inflammatory bowel disease

Inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis can cause bloody stool.

Anal fistula

An anal fistula is a small tunnel that forms between the end of the bowel and the skin near the anus.

It typically develops when an infection near the anus causes pus to collect in surrounding tissues. As the pus drains, it leaves behind the fistula, which may continue to ooze pus or blood.

Medication

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

  • warfarin (Coumadin)
  • enoxaparin (Lovenox)
  • apixaban (Eliquis)

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

Colon polyps

Colon polyps can lead to bloody stools. These small growths may be benign or precancerous.

Cancer

Cancerous tumors of the GI tract can weaken the lining of the GI tissues, causing them to bleed.

Bloody stool may be especially common in infants. Some causes include:

  • Food allergies: Allergies to proteins in food or milk can cause gastroenteritis that leads to intestinal bleeding.
  • Structural gastrointestinal abnormalities: Issues that cause the intestines to become twisted — such as intestinal malrotation and volvulus — may lead to bleeding.
  • Necrotizing enterocolitis: This serious disease causes inflammation and tissue death within the large intestine, and it usually affects premature or newborn babies. The disease can cause:
    • blood in stool

A doctor will first ask how much blood was visible in the bowel movement, and they may also order a test called a complete blood count to help determine the extent of the blood loss.

The next steps depend on how much blood was lost.

Emergency situations

If a person reports a large amount of blood loss and has a low blood count, the doctor may perform an urgent endoscopy. This involves inserting a thin, flexible tube with a camera at one end into the GI tract to look for the source of the bleeding.

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

If the doctor is unable to identify and 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 a:

  • Fecal occult blood test: This involves analyzing a stool sample for the presence of blood.
  • 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 approach 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.

In some cases, surgery is necessary to prevent further bleeding. The doctor may perform it using endoscopy or colonoscopy. The procedure 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

If any of the following occur, seek emergency medical attention:

These symptoms could indicate that the person is losing a dangerous amount of blood.

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

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

Blood in stool can be alarming, but it is not always a cause for concern. The cause may be relatively harmless and heal on its own.

However, if the bleeding is persistent, seek medical advice. This is especially important if the bleeding accompanies pain.

Anyone who notices a lot of blood in a bowel movement should receive emergency care, especially if they also experience dizziness, fatigue, a rapid heartbeat, or shortness of breath.