Digestive Disorders > Symptoms

Black stool – Where does dark and black stool come from?

Dr. med. Andre Sommer

Dr. med. Andre Sommer

Black bowel movements can be a sign of serious illness. Sometimes, however, intensely colored foods such as blueberries, liquorice or red wine cause a dark stool color. In addition, food supplements such as iron supplements can also be to blame for the black color. However, if the stool is deep black, shiny and smells extremely bad, it is usually tarry stool (malana). If you experience this, you should immediately see a doctor. They can clarify possible causes and advise on the treatment options.

What does a black bowel movement mean?

Those who find the shiny black, foul-smelling stool in their toilet for the first time often get a scare. But there isn't always something bad behind it. Tar stool arises when blood is added to the feces during the digestive process. Unlike light bloody stool, however, it rarely comes from the large intestine. Instead, it usually gets into the chyme in the stomach or duodenum. And that's why the bowel movement is black: If the red blood pigment hemoglobin comes into contact with stomach acid or digestive juices, it is either converted into black haematin by the stomach acid or it breaks down the bacteria in the small intestine. This creates a black mass with a consistency similar to coffee grounds. A doctor urgently needs to clarify where exactly the blood is coming from. In people who digest very slowly due to improper nutrition or a metabolic disorder, the blood can also come from the large intestine.

How do I recognize tar stool?

Dark colored stool can have many causes, for example it can arise from the color of certain foods **or **taking certain medications. Anyone who has eaten blueberries, cherries or licorice, takes coal tablets or iron supplements should wait a few days. If the droppings then return to their usual color, everything is fine. Affected persons can recognize the more dangerous tar stool by the fact that it is not only darker than usual, but also pitch black. It also shines conspicuously. And it has an extremely foul smell. Depending on the cause, you may also experience abdominal pain, diarrhea, nausea, or vomiting with blood. Anyone who experiences these symptoms should see a doctor as soon as possible.

How does the doctor diagnose black bowel movements?

If a patient presents himself to his doctor with suspected tar stool, he must first provide a stool sample. The doctor also asked him about the consistency of the feces, the frequency of bowel movements and the eating habits. Together with the examination of the stool sample, this often gives him important clues as to the cause of the tar stool. To determine the exact location of the bleeding, the doctor performs a gastroscopy or colonoscopy (by endoscopy).

How is tar stool produced?

If food and pharmaceuticals are excluded as the cause of black bowel movements, it is clear that bleeding must have occurred somewhere in the upper part of the gastrointestinal tract. This can happen in the esophagus, stomach or duodenum. **The blood mixes there with digestive juices **that break down the red blood pigment (hemoglobin). This gives it its deep black color.

What drugs can stain the stool black?

Some medications can make the stool black during the time of ingestion. This causes confusion for many, but has no disease value. These medications and supplements include:

  • Iron supplements
  • **Bismuth or bismuth preparations **(stool color is black-gray)

    • Bismuth subsalicylate **(e.g. **Pepto-Bismo)
  • Charcoal tablets
  • Roboranzien (strengthening / tonic)

What foods can make the stool dark or black?

Very dark or red foods can turn the stool black. These foods include:

  • Licorice
  • Beetroot
  • Red wine
  • Blueberries
  • Black pudding

Long-term abnormalities in the stool can also be treated with the help of the diet. We have developed a nutritional therapy program that is tailored to your symptoms for this purpose. Find out more about therapy here.


What diseases can black stool (tar stool) indicate?

Tar stool may indicate bleeding in the esophagus, stomach, or duodenum, which can be a symptom of various gastrointestinal disorders. The causes include:

Cause of blackening Frequency Description
Stomach ulcer (Peptic ulcers) 45% Stomach ulcers are one of the most common causes of tar stool. They usually arise from inflammation of the gastric mucosa. Other symptoms include stinging abdominal pain, nausea and nausea.
Ruptured esophageal varices 25% Increased portal pressure can cause varicose veins in the esophagus or stomach. If these burst, the high blood loss can be life-threatening. Symptoms include tar stools and bloody vomiting. If a varicose vein burst is suspected, the emergency doctor should be called.
Mallory-Weiss syndrome 15% With this disease, severe vomiting causes tears in the esophageal mucosa - alcoholics or people with bulimia are often affected.
Mucosal damage (Erosions) 5% If the mucous membranes in the esophagus, stomach or duodenum are damaged, bleeding can occur which leads to tar stool.
Stomach cancer 5% Gastric cancer develops on the gastric mucosa and shows hardly any symptoms in the early stages. Later, however, black bowel movements may occur.
Hemolytic anemia ? A type of anemia that causes red blood cells to break down. Due to this decay (hemolysis), the stool turns black. This can have congenital causes, for example sickle cell anemia or acquired causes, for example infections, side effects of medication.
Esophagitis ? Inflammation of the esophagus is associated with heartburn, difficulty swallowing, sometimes vomiting, diarrhea and black bowel movements.
Nosebleeds ? Ingested blood from heavy nosebleeds can turn the stool dark to black.

Rarer causes for black bowel movements are, for example, duodenal cancer, vascular abnormalities and biliary ulcers.

How is black stool treated?

Which treatment the doctor chooses for tar stool depends to a large extent on the underlying disease. But first he has to stop the bleeding that is causing the black bowel movements. To locate the cause, he examines the stomach with the endoscope. It is also possible to take hemostatic measures directly via a working channel of the endoscope. Drug options are also available. If none of these remedies stop the bleeding, surgery can be considered. However, a doctor must decide which is the best variant in individual cases. In any case, tar stool needs medical clarification, as it can be an indication of serious illnesses.

Why does my child have black bowel movements?

Black bowel movements are perfectly normal in newborn babies. They often swallowed the mother's blood at birth - as well as amniotic fluid, bile and intestinal mucus. Usually, bowel movements normalize after two days at the latest. The black, very sticky stool of newborns is called meconium.

Is black stool normal when I am pregnant?

Those who are pregnant and have black bowel movements usually do not need to worry. Since women often suffer from iron deficiency and this substance is important for the healthy development of the fetus, most pregnant women take an iron supplement. The iron oxidizes in the digestive tract, causing the stool to turn dark green to black. If you are unsure or are not taking any iron supplements, be sure to contact a doctor.


Koelz, H.R. and Arn, M., 2006. Neue Epidemiologie der akuten gastrointestinalen Blutung. Der Chirurg, 77(2), pp.103-110. Online: https://link.springer.com/article/10.1007/s00104-005-1142-7

Adler, G., Beglinger, C., Manns, M.P., Müller-Lissner, S. and Schmiegel, W. eds., 2013. Klinische Gastroenterologie und Stoffwechsel. Springer-Verlag. Online: https://www.springer.com/de/book/9783642629778

Goralnick, E. and Meguerdichian, D.A., 2014. Gastrointestinal bleeding. Rosen’s emergency medicine concepts and clinical practice, ed, 8, pp.248-253. Online: https://pdfs.semanticscholar.org/25a1/11b152d05ecd5594990c5104499aedebcd43.pdf

Dr. med. Andre Sommer

Dr. med. Andre Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara.

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