What Can Cause Red Stool or Black Stool?

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

Strawberry gelatin
Red foods could lead to red stools. Check your diet for red dyes or even foods that are naturally red. Image © john shepherd / E+ / Getty Images

Having red stools or black stools can cause a shock when you don't know why it is happening. Common reasons for a change in stool color include eating certain foods (especially those with artificial colors) and taking dietary supplements (such as iron). The cause of red stools or black stools could be nothing to worry about, such as those that are caused by food coloring. It's important to keep in mind, however, that red or black in the stool could 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 and easily treated problems such as hemorrhoids. Find out if the change in your stool could be from something you ate or if you actually do need to call your doctor.

Medical Causes of Black Stool

The medical term for stools that are black and foul smelling because they contain blood is "melena." To figure out how much blood is present in a black stool a physician may order a fecal occult blood test. Melena can be caused by 200 milliliters (or more) of blood being passed in the stool, which is also equivalent to a quarter of a cup, or 4 tablespoons. The darkened color of the blood is a sign that the bleeding is coming from somewhere higher up in the digestive tract (the stomach or the small intestine) and not from the lower part, or the colon. If you think there is blood in your stool, contact your doctor immediately to have the cause checked out.

This type of bleeding might be caused by:

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 over-the-counter or prescription pain medications called 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.

Harmless Causes of Black Stool

A black stool caused by food, supplements, medication, or minerals (but not blood) might be called "false melena." The stool might be black, but it doesn't actually contain any blood. 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. Food and supplements that can cause black stool are:

Medical Causes Of Red Stool

Stool that is red or maroon colored because it contains blood is called "hematochezia." The brighter color of the blood is because it is coming from somewhere lower in the digestive tract (like the colon or the rectum). If you see blood in the stool, it should always be checked out by a doctor.


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 to be evaluated by a physician to see if prescription medication is needed.

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 that are done at home.

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 start of 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 discovered with a simple stool test. The fecal occult blood test may be done as a screening tool for colon cancer.

IBD and diverticular disease are also sources of bleeding from the digestive 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.

Harmless Causes Of Red 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

When Is Dark Stool Serious?

Blood in the stool may not always be the result of a serious or chronic condition, but it should always be checked out 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 gastroenterologist. This is true even in the setting of IBD or other chronic illnesses, because treatments might need to be changed.


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

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

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