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What Can Cause Red Stool or Black Stool?

If You Suspect Blood In Your Stool, Get Evaluated By A Doctor


Updated June 16, 2014

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A change in stool color can cause a lot of stress when you don't know why it is happening. Common reasons for a change in stool color include foods (especially those with artificial colors) and dietary supplements. The cause of red stools or black stools could be benign, such as food coloring, but could also be from bleeding in the gastrointestinal tract (the stomach, small intestine, or large intestine). Blood is a warning sign for both serious digestive problems such as colon cancer and relatively common problems such as hemorrhoids.

Causes Of Black Or Dark Stool

The medical term for passing stools that are black and foul smelling due to the presence of blood is "melena." To detect how much blood is passed in a black stool a physician may order a fecal occult blood test. Melena is diagnosed if 6 tablespoons (200 milliliters) of blood or more was passed in the stool. The darkened color of the blood usually indicates that the bleeding is coming from higher up in the gastrointestinal tract and not from the lower part, or the colon. This type of bleeding might be caused by:

A black stool caused by food, supplements, medication, or minerals (but not blood) is known as "false melena." Iron supplements, taken by many women to combat iron-deficient anemia, may cause stools to be black or even greenish in color. Multivitamins that contain iron may also have the same effect. In addition, foods that are dark blue or black in color may cause black stools. Substances that can cause false melena are:

An ulcer is a sore on the lining of the stomach which can cause bleeding. Stomach ulcers are typically caused either by infection with a bacterium called Helicobacter pylori (H. pylori) or by use of pain medications known as NSAIDs (nonsteroidal anti-inflammatory drugs).

Gastritis is the inflammation of the stomach lining and can be caused by overindulging in alcohol or food, eating spicy foods, smoking, infection with bacteria or prolonged use of NSAIDs. Conditions which can lead to gastritis include pernicious anemia, autoimmune diseases, and chronic bile reflux.

Causes Of Red Stool

The passage stool that is red or maroon colored due to the presence of blood is called "hematochezia." The brighter color of the blood indicates that it may be coming from a source in the lower gastrointestinal tract. A physician should investigate blood in the stool to rule out any potentially serious conditions. Causes of red blood in the stool can include:

A common source of bright red blood in the stool or on toilet paper is hemorrhoids. Hemorrhoids are enlarged veins in the rectal area that may burst and bleed. Hemorrhoids are not usually serious, and can often be treated effectively with over the counter medications. Troublesome hemorrhoids that won't heal may need the attention of a physician or prescription medication.

A fissure is a tear or ulcer in the lining of the anal canal (the last part of the rectum before the anus). Fissures can occur in anyone, but are more common in middle age or young adults and can cause bright red bleeding. Acute fissures generally heal with non-invasive treatments.

Colon polyps can also cause red blood to appear in the stool. Polyps are growths on the inside of the colon that are believed to be the precursors to colon cancer. Blood that may be from polyps or colon cancer is not always visible in or on the stool. This type of blood is called "occult blood," and can be identified with a simple stool test. The fecal occult blood test may be done as part of a screening panel for colon cancer.

IBD and diverticular disease are also sources of bleeding from the gastrointestinal tract. Both Crohn's disease of the colon and ulcerative colitis can result in blood passed in the stool, frequently along with diarrhea. Pouches in the colon wall (known as diverticula) caused by divercular disease may produce considerable amounts of blood in the stool.

Finally, several different types of food with natural or artificial coloring may also cause red colored stools. These can include:

  • red gelatin, popsicles, or Kool-Aid
  • tomato juice or soup
  • large amounts of beets

Blood in the stool may not always be the result of a serious or chronic condition, but it should always be checked by a physician. Any change in bowel habits, such as color, odor, frequency, or consistency (constipation or diarrhea) that does not clear up within a few days is reason to make an appointment with a family practitioner or a gastroenterologst.


Heller JL. "Bloody or tarry stools." A.D.A.M. 7 Jan 2011. 4 Sept 2013.

Johns Hopkins Children's Center. "Gastrointestinal Bleeding or Blood in the Stool." The Johns Hopkins University. 2013. 10 Aug 2013.

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