Possible Causes of Bloody Stool

Blood in the stool happens because there is bleeding somewhere in the gastrointestinal (GI) tract. This is the system of organs that takes in food, digests it, and expels waste. Because bleeding can occur anywhere along the GI tract, from mouth to anus, bloody stool can have a number of causes.

Blood in the stool usually looks blood-red or maroonish. Blood that comes from the upper GI tract and is digested as it moves through the gut may look different. This blood is called melena and looks black and tar-like.

Because blood in the stool may be a symptom of something serious, like cancer, it should never be ignored. Always see a doctor if you find blood in your stool. A physical exam, lab tests, and details from your personal history can help a doctor find the cause.

This article discusses some of the possible reasons for blood in the stool.

potential causes of bloody stool

Verywell / Laura Porter

Upper GI Bleed

Blood in your stool may come from the upper GI tract. The most common cause of this is peptic ulcer disease. Ulcers are sores in the lining of the stomach or upper intestine. Blood from a peptic ulcer can be red or it can be black and tarry.

An upper GI bleed can be diagnosed with an endoscopy. During this procedure, a gastroenterologist looks at your upper GI tract with a camera attached to a narrow, flexible tube. The tube is passed down your throat to your gut.

If you have serious upper GI bleeding, you will need surgery.

Anal Fissure

Anal fissures are the most common cause of bloody stool in infants, but adults can get them too. The blood from anal fissures is bright red in color.

Anal fissures are caused by constipation, or large, firm stools that are hard to pass. This can cause a crack in the skin. Stretching the skin of the anus makes fissures visible.

Fortunately, anal fissures usually heal on their own. You can treat the pain and discomfort with petroleum jelly. Drinking more water and eating high-fiber foods can help soften your stools. 

Polyps

A polyp is a small growth on the lining of your intestinal tract. There are a few different types of polyps. Adenomatous polyps are some of the most common. These polyps grow on the lining of the colon, or large intestine. About 25% of adults aged 50 and over have this type of polyp.

Adenomatous polyps can develop into colorectal cancer, or cancer of the colon or rectum. Colorectal cancer is the third most common cause of cancer-related deaths in the United States.

Although most cases of colorectal cancer develop from adenomatous polyps, only around 5% of polyps will become cancerous.

Polyps often have no symptoms, but sometimes they can cause bloody stools. The blood can be red or dark and tarry.

Polyps can be removed before they become cancerous. If they do progress to cancer, the cancer is treatable if caught early. That is why all people age 45 and older should be regularly screened for colorectal cancer. This can be done with a colonoscopy or stool-based test.

Hemorrhoids

Hemorrhoids are swollen blood vessels that can bulge from the anus. Hemorrhoids are often uncomfortable. They can be painful or itch. Because there are a lot of blood vessels around the anus and rectum, hemorrhoids may bleed bright, red blood.

You may be at risk for hemorrhoids if you:

  • Have chronic diarrhea
  • Are frequently constipated
  • Do a lot of heavy lifting
  • Sit for long periods of time
  • Are pregnant

Surgery is an option if your hemorrhoids are severe, but most hemorrhoids do not require surgery. Eating more fiber or using a salve like Preparation H can help.

Gastroenteritis

Gastroenteritis is an illness of the stomach and intestines. It can be caused by a virus, bacteria, or parasite. Sometimes, gastroenteritis can cause bloody diarrhea. This is more common in bacterial gastroenteritis.

Food poisoning is a type of gastroenteritis. Bacteria that commonly cause food poisoning include:

  • Campylobacter
  • E. coli
  • Listeria
  • Salmonella

Most of the time, gastroenteritis gets better on its own, but see a doctor if your symptoms last for more than one or two days.

Angiodysplasia

Bloody stool that can't be explained is often caused by angiodysplasia. Angiodysplasia can happen as the blood vessels in the gut age or weaken. This type of bleeding can be red or dark and tarry.

Angiodysplasia is common during end-stage renal disease (kidney disease) or renal failure. People with a common genetic bleeding disorder called von Willebrand disease may also have angiodysplasia.

Angiodysplasia can be treated in a few different ways, including:

  • Removal during endoscopy
  • Hormone therapy
  • Blood transfusions
  • Iron supplements.

Fortunately, in most people, angiodysplasia disappears on its own.

Inflammatory Bowel Disease (IBD)

Inflammatory bowel disease (IBD) is an autoimmune disease of the bowels. When you have an autoimmune disease, your immune system attacks part of your own body. In IBD, this leads to inflammation and damage of the intestines.

Crohn's disease and ulcerative colitis are the two most common types of IBD. Symptoms can include bloody stool, which may be red or dark and tarry.

IBD can be treated in a few different ways:

  • Steroids
  • Immune-modifying agents
  • Surgery

Fortunately, new drugs are reducing the number of IBD patients who need surgery.

Cancer

Because blood in the stool may be a symptom of colorectal cancer, it is important to see a doctor if you notice this symptom. Bleeding from colorectal cancer may be red or dark and tarry.

Colorectal cancer was once thought to mostly affect people over the age of 50. Recent research, however, found that this cancer is also the third leading cause of cancer-related death in adults younger than 50.

There is good news, though. Thanks to earlier detection and treatment, the five-year survival rate for patients with colorectal cancer has been steadily increasing over time.

Diverticular Disease

Diverticula are abnormal pouches that can form in your lower intestine. There are two types of diverticular disease.

The simple presence of diverticula is called diverticulosis. Sometimes, though, diverticula become infected or inflamed. When that happens, the disease is called diverticulitis.

Both forms of diverticular disease can cause pain and blood in the stool. When diverticular disease causes bleeding, it will usually appear suddenly and be red or maroon in color.

Diverticula grow out of weaknesses in the wall of your colon. Sometimes they can grow to be several centimeters in size. The disease is often blamed on a low-fiber diet, but the true cause is unknown.

A surgeon can stop bleeding from diverticula during an endoscopy or abdominal surgery. Diverticula can be treated in or out of a hospital. Diverticulitis can often be successfully treated with antibiotics.

Ischemic Colitis

Ischemic colitis happens when the blood vessels that supply the large intestine are narrowed or blocked. Most cases of ischemic colitis happen in elderly people. The condition can be short-term or long-term. Symptoms include:

  • Red blood in the stool
  • Diarrhea
  • An urgent need to defecate
  • Abdominal pain and vomiting

Most cases of ischemic colitis last a short time and resolve on their own. Sometimes, though, people with severe cases of ischemic colitis need to be hospitalized. Patients with severe disease may need intravenous (IV) fluids, antibiotics, and bowel rest, or a restricted diet.

About 20% of people who develop ischemic colitis end up needing surgery. Unfortunately, surgery for ischemic colitis is very dangerous. Up to 65% of patients who have this surgery will die.

False Alarm

Sometimes, what looks like bloody stool is really just coloring from something you've eaten. Dyes used in some fruit punch and gelatin can make your stool red. Beets may do the same thing.

Summary

Blood in the stool can have a number of causes. Hemorrhoids and anal fissures are annoying and painful, but not harmful.

Some causes of gastrointestinal bleeding may require surgery, including upper GI bleeds, polyps, angiodysplasia, inflammatory bowel disease, diverticular disease, and ischemic colitis.

Sometimes, blood in the stool can be a symptom of something serious, like cancer. Blood in the stool may also be a false alarm.

A Word From Verywell

It is important to see a physician if you find blood in your stool. It can be scary to see blood on toilet tissue or in the bowl, and you might be tempted to ignore it and hope it goes away. But because colorectal cancer is a leading cause of death, even for people under the age of 50, you should never ignore blood in your stool.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
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  • Stephan M, Carter C, Ashfaq S. Chapter 50. Pediatric Emergencies. In: Stone C, Humphries RL. eds. CURRENT Diagnosis & Treatment Emergency Medicine, 7e. New York, NY: McGraw-Hill; 2011.

  • Usatine RP, Smith MA, Chumley HS, Mayeaux EJ, Jr.. Chapter 66. Hemorrhoids. In: Usatine RP, Smith MA, Chumley HS, Mayeaux EJ, Jr.. eds. The Color Atlas of Family Medicine, 2e. New York, NY: McGraw-Hill; 2013.