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What Are the Causes of Black Stool Color?

author image Sarah Harding
Sarah Harding has written stacks of research articles dating back to 2000. She has consulted in various settings and taught courses focused on psychology. Her work has been published by ParentDish, Atkins and other clients. Harding holds a Master of Science in psychology from Capella University and is completing several certificates through the Childbirth and Postpartum Professional Association.
What Are the Causes of Black Stool Color?
Dark-colored foods can cause black stool color. Photo Credit blueberries image by Horticulture from Fotolia.com

An unusual color of stool can be alarming, but it is not always a cause for concern. If fecal matter is dark black, tarry or bloody, especially on a recurrent basis, medical treatment is necessary. The University of Maryland Medical Center (UMM) explains that passing black stools can be due to an issue that exists anywhere within the entire digestive system. The digestive system includes everything from the mouth to the anus.


A number of foods and medicines can lead to black stools. In most cases, eating such foods or pills will only cause a temporary bout of darkened stools. The UMM says these consumable items include black licorice, lead, iron pills, medicines containing bismuth and blueberries.

Blood Vessel Issues

Any abnormality in the blood vessels within the digestive tract can cause bleeding, which will appear as black stool after passing through the digestive system. The UMM identifies specific blood vessel issues such as vascular malformation, bowel ischemia, esophageal varices and stomach varices. When a vascular malformation occurs, the blood flow can be constricted or a cluster of blood vessels can develop abnormally. The Cincinnati Children's Hospital explains that this is a defect present at birth, but it may not be identified until an issue, such as black stools, develops. Bowel ischemia causes constriction and reduced blood flow to the bowel lining, specifically the intestines.

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A number of components in the digestive tract can become inflamed, causing black stools. Inflammation can be the result of an infection or irritation. Some foods can trigger the irritation, depending on the individual's health issues. Some digestive problems, like Crohn's disease or irritable bowel syndrome (IBS), can make a person prone to unusual stools, including black and tarry matter. The UMM points out that the use or overuse of medications like ibuprofen, naproxen or aspirin is often to blame for persistent inflammation and ulcers within the digestive system.


An ulcer is an open wound that can develop within the digestive system. It can cause internal bleeding that is excreted as black stool, or it can cause a person to pass bloody stools when the ulcer is near the end of the digestive tract. The Mayo Clinic explains that in order for blood to be the cause of black stools, the bleeding would have to take place in the upper section of the digestive tract, such as the stomach.

Similar to an ulcer, a wound inside the digestive tract caused by puncture or other trauma can cause black stools, explains the UMM. Ulcers are typically caused by stomach acids and other internal digestive processes, whereas another type of wound can be the result of blunt force.

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