Black diarrhea should not be ignored. It is often a sign of bleeding in your digestive tract, which can have numerous causes depending on where the bleeding is coming from. The source of bleeding can be located anywhere from your nose or mouth to your large intestine. Black diarrhea caused by bleeding is called melena. Stools may also appear black from non-bleeding causes, such as certain foods, supplements and medicines.
Mouth, Nose, Throat and Esophagus Bleeding
Brisk bleeding from any problem in the mouth, nose or throat may be swallowed, producing melena. As blood travels through the digestive tract, acid in the stomach, other digestive juices and bacteria break it down, changing it from red to black. When mixed with stools, this will make the stools appear black, like tar.
Bleeding from ulcers or inflammation in the esophagus -- the tube connecting the throat to the stomach -- can also produce melena. These conditions may be caused by infections or backup of stomach acid into the esophagus, as in gastroesophageal reflux disease. Cancer of the esophagus may bleed, producing melena, but this is usually a late symptom. Weight loss and swallowing problems are generally earlier warning signs of this cancer.
Sometimes bleeding results from a tear in the wall of the esophagus -- called a Mallory-Weiss tear. These tears are typically caused by repeated forceful retching and vomiting. Swollen veins in the wall of the esophagus -- esophageal varices -- may also produce melena. They are typically caused by cirrhosis of the liver. Both Mallory-Weiss tears and varices may cause severe, life-threatening bleeding, which often results in vomiting up blood as well as melena.
Bleeding from the stomach is another possible source of melena. When bleeding is brisk, vomiting may also occur. In this case, stomach acid breaks down the blood, producing a dark brown color. The vomited material typically resembles coffee grounds.
Stomach ulcers are a common source of bleeding from the stomach. These ulcers may be caused by infection with the bacteria Helicobacter pylori, excess stomach acid or stomach cancer. Stomach bleeding may also be caused by generalized inflammation of the stomach, called gastritis. This typically results from infections, alcohol excess, stress or certain medications, especially nonsteroidal anti-inflammatory drugs (NSAIDs).
Small Intestine Bleeding
Bleeding in the small intestine may also produce melena. Ulcers are a common cause of small intestine bleeding. They usually occur in the first part of the intestine, known as the duodenum. H. pylori infection is the most common cause of duodenal ulcers, according to Merck Manual.
Crohn disease is an inflammatory disease that can be found anywhere in the digestive tract but commonly occurs in the last part of the small intestine, called the ileum. It produces inflammation and ulcers that can bleed.
Large Intestine Bleeding
Bleeding from the large intestine -- or colon -- usually causes frank red blood in the stools instead of black diarrhea. But if the bleeding occurs slowly or originates from the first part of the colon, the stools may appear black. Colon cancer and angiodysplasia are two conditions in the large intestine that usually produce slow bleeding. Angiodysplasia is an area of abnormal blood vessels that can occur anywhere in the digestive tract. These blood vessels are weak and have a tendency to bleed.
Foods, Supplements and Medicines
Certain foods can cause black stools. They may or may not cause the stools to be diarrhea-like as well. Black licorice is one of the most common offenders. Blood sausage and very bloody meats can also cause black stools. Dark colored fruits and vegetables, such as blueberries, blackberries, prune juice and beets are other possible causes.
Iron supplements are a common source of black stools, although they often cause constipation instead of diarrhea. Another cause of black stools and possibly diarrhea is bismuth, the active ingredient in several medicines used for stomach symptoms, such as Pepto-Bismol and Kaopectate. The antacid Maalox may also cause black diarrhea.
Seeking Medical Attention
If you have black stools, see your doctor promptly unless you have eaten a food or taken a supplement or medicine known to cause black stools. Seek immediate medical attention if you have a large amount of black diarrhea or your black stools are accompanied by abdominal pain, vomiting, lightheadedness or fainting.
Reviewed by Mary D. Daley, M.D.
- Gastroenterology: Clinical Cases Uncovered; Satish Keshav, et al.
- Primary Care Medicine: Office Evaluation and Management of the Adult Patient; Allan H. Goroll, et al.
- Interpreting Signs and Symptoms; Helen C. Ballastas, et al.
- Merck Manual Professional Version: Peptic Ulcer Disease
- Medline Plus: Black or Tarry Stools
- Merck Manual Professional Version: Overview of Gastritis
- Mayo Clinic: Stool Color -- When to Worry