Common Causes of Red or Black Stool

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Red or black stools can be a shock when you don't know what caused them. It's not always something to worry about, though.

The reason for a change in stool color could be as simple as something you ate. Foods with artificial colors are a common culprit. Certain supplements, like iron, may also cause discolored stools.

Still, it's important to remember that red or black stools could be caused by bleeding in the gastrointestinal (GI) tract. This includes the stomach, small intestine, or large intestine.

Blood is a warning sign for digestive problems, both serious and relatively harmless. While easily treated problems like hemorrhoids can cause blood in the stool, so can colon cancer. This is why it's important not to ignore changes in stool color.

This article discusses some of the reasons for red or black stools, and how to know the difference between dietary causes and those that need to be evaluated by a doctor.

Black vs. Red Stool Medical Causes

Verywell / Jessica Olah

Food or Medication Causes

Foods are a frequent cause of discolored stools. This is especially true for foods that contain artificial colors. If your discolored stools are caused by something you ate, the color should go back to normal once the food has been digested and is out of your body.

Black Stool

Melena is black stool caused by GI bleeding. When black stools are caused by something you ingested, they are called "false melena." Some of the things that can cause false melena include:

  • Food
  • Supplements
  • Medications
  • Minerals

Iron supplements can help combat iron-deficiency anemia. They may also cause stools to be black or even greenish in color. Multivitamins that contain iron may have the same effect. Foods that are dark blue or black in color may also cause black stools.

Food and supplements that can cause black stool include:

Red or Maroon Stool

Some foods with natural or artificial coloring may cause red stools. These include:

  • Red gelatin, popsicles, or Kool-Aid
  • Tomato juice or soup
  • Large amounts of beets

Red stools in babies may be caused by the popular antibiotic Omnicef, which is often used for ear infections. However, because being on antibiotics can cause an infection of the intestinal tract called C. difficile, always call your healthcare provider if your baby has red stools.

Recap

Red and black stools can be caused by something you ate, or a supplement you took. Your stool should return to a normal color as soon as the substance is out of your system.

Medical Causes of Black Stool

True melena is black and foul-smelling. This is because it contains blood. If you have melena, your doctor may order a fecal occult blood test. This will help determine how much blood is in your stool.

Melena can be caused by 200 milliliters or more of blood passed in the stool. This is equal to a quarter cup or four tablespoons.

The dark color of the blood is a sign that the bleeding is higher up in the GI tract, in the stomach or the small intestine.

If you think there is blood in your stool, contact your doctor at once. It is important to find the cause of the bleeding.

Bleeding Ulcer

An ulcer is a sore anywhere along the lining of the stomach or intestine. Ulcers can sometimes bleed.

Ulcers usually have one of two causes:

Gastritis

Gastritis is an inflammation of the stomach lining. It can have various causes, including:

  • Overindulging in alcohol or food
  • Eating spicy foods
  • Smoking
  • Infection with bacteria
  • Prolonged use of NSAIDs

Certain medical conditions can also lead to gastritis. These include:

Bleeding in the Esophagus

A few medical conditions can cause bleeding in the esophagus. These include:

  • Esophageal varices, swollen veins in the esophagus
  • A tear in the esophagus caused by violent vomiting
  • Esophagitis, inflammation of the esophagus

Recap

Black stool that contains blood is called melena. The blood usually comes from higher in the GI tract. Some causes include ulcers, gastritis, and bleeding in the esophagus. 

Medical Causes of Red or Maroon Stool

Red- or maroon-colored stool that contains blood is called hematochezia. The brighter color is because the blood is coming from lower in the digestive tract, like the colon or the rectum.

Red blood in the stool can have a number of medical causes. Always see a doctor if you find blood in your stool.

Hemorrhoids

Hemorrhoids are a common source of bright red blood in the stool or on toilet paper. These are enlarged veins in the rectal area that may burst and bleed.

Hemorrhoids are not usually serious. They can often be treated with over-the-counter medications. Hemorrhoids that won't heal may need to be seen by a doctor. Prescription medication can help.

Anal Fissure

An anal fissure is a tear or ulcer in the lining of the anal canal. The anal canal is the last part of the rectum before the anus.

Anyone can get fissures, but they are most common in middle-aged people and young adults.

Fissures can cause bright red bleeding. They usually heal with home care.

Colon Polyps and Colon Cancer

Colon polyps can also cause red blood in the stool. Polyps are growths on the inside of the colon. Sometimes they can turn into colon cancer. Colon cancer may also cause blood in the stool.

Blood from these sources is not always visible in or on the stool. Blood that isn't visible is called occult blood.

A fecal occult blood test looks for this kind of blood. This test may be done to screen for colon cancer.

Digestive Disorders

Inflammatory bowel disease (IBD) is a name for conditions that cause inflammation of the bowel. These conditions can cause bleeding in the digestive tract. Both Crohn's disease of the colon and ulcerative colitis can cause bloody stool, often with diarrhea.

Diverticular disease can also cause red blood in the stool. Diverticula are pouches that form in the wall of the colon. People with this condition may have large amounts of blood in the stool.

Recap

Red blood in the stool could have harmless causes, like hemorrhoids and anal fissures. It could also be related to something more serious, like colon polyps, colon cancer, or a digestive disorder.

When to See a Healthcare Provider

Blood in the stool may not always be serious. Still, it is important to have this symptom checked out by a doctor.

This is true even when you already have a diagnosis of IBD or another chronic illness. Blood in the stool may mean your treatment needs to be changed.

See a doctor if:

  • You have changes in color, odor, or frequency of stools.
  • You can't think of any food or supplements that could explain the color change.
  • The color change lasts a few days.
  • You have other symptoms, like diarrhea, constipation, weakness, or dizziness.

If you have obvious blood in the stool or are passing blood with no stool, see a doctor at once. If there is extreme pain and blood loss, go to the emergency room or call 911.

Summary

Red or black stools could be caused by something harmless, like food or a supplement. Sometimes, though, they can be caused by bleeding somewhere in your GI tract.

Stomach problems like ulcers and gastritis may cause black stools. Bleeding in the esophagus can also cause this.

Red blood in stool is caused by bleeding lower in the GI tract. Hemorrhoids and anal fissures can cause it. More serious causes can include colon polyps, colon cancer, and digestive disorders like inflammatory bowel disease and diverticular disease.

Always see a doctor if you notice blood in your stool.

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5 Sources
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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