Black Stools: 6 Common Causes & What to Do

Clinical review: Dr. Antonio Carlos Moraes
Gastroenterologist
June 2022

Dark or black stool usually occurs when there is digested blood mixed in the feces. It is often a sign of bleeding at the beginning of the digestive tract, near the esophagus or stomach. Bleeding in these areas can happen due to ulcers or varices. 

Black poop can also happen with more minor coincidences, like with diets that are rich in iron or with people who take iron supplements. Some medication can also cause darker stools. 

Nonetheless, if your black stools persist for more than 2 days, you should see your doctor for assessment. A stool test will likely be ordered, and the doctor may also opt to send you for a colonoscopy. Once the underlying cause is identified, appropriate treatment can be initiated. Learn more about what different colors of poop can mean

The most common causes of black stools are: 

1. High iron intake

Diets that are high in iron and contain plentiful amounts of beans, red meat or beets may result in darker stools. When foods with high iron contents are consumed, the intestine may not be able to absorb all the iron into the body, and eliminates excesses in the stool. Iron will often give the stool a black color.

It is important to note, however, that dark stools from high iron will not have any changes to odor. Stools with blood, on the other hand, will have a more distinct smell. 

What to do: There is no need to consume an exaggerated amount of iron every day unless medically indicated. Reduce your iron intake and monitor your stool color, as it should return to its normal, lighter color within a few days. 

2. Intake of red or black foods

In addition to foods with high iron contents, foods with a very intense red or black color can also darken poop. Some examples include:

  • Licorice
  • Blackberries 
  • Dark chocolate
  • Jello with red food coloring
  • Beets

What to do: If you suspect that your stool color has changed due to your diet, monitor the types of food you eat and avoid very intensely-colored foods. If your black stools persist after a few days of monitoring, you should see your doctor for doctor. 

3. Medication or supplement use

Some supplements, like iron and lead pills, can lead to black poop after their first days of use. Other medications that can cause black stools are anticoagulants and anti-inflammatories.

What to do: If you notice that your stool color has become darker within a few days of starting a new medication or supplement, you should advise your prescriber so that he or she can assess whether the medication is safe to continue.

4. Stomach ulcers

Stomach ulcers, also known as gastric ulcers, are lesions that form on the stomach lining. They can cause symptoms like stomach pain, vomiting and bleeding, which is then noted in the stools. Stools that contain blood will have an intensely foul odor and will be much darker than usual. Read more about what causes stomach ulcers and other symptoms you may experience.

What to do: Treatment for stomach ulcers is usually monitored by a gastroenterologist. Goals will be to treat the underlying cause, and may involve using medication to reduce or neutralize stomach acid. 

5. Esophageal varices

Esophageal varices occur when the blood vessels in the esophagus become dilated. This usually happens as a consequence of liver disease. Rupture of these vessels can lead to vomit with blood as well as blood in the feces, which gives stool a black color. You may also experience pallor, dizziness, and shortness of breath. 

What to do: Treatment for esophageal varices will depend on the severity, amount of bleeding and the underlying cause. Mild cases can be conservatively treated with medication, while more severe cases of vessel rupture will require surgical repair. 

6. Stomach or intestinal cancer

Stomach or intestinal cancer can also lead to dark stools due to increased senstivity and risk for bleeding in these organs. 

What to do: Treatment for cancer, which is monitored by an oncologist, is aimed at destroying cancer cells and decreasing the risk for spreading. It may involve chemotherapy, radiation therapy and/or surgery. 

Black stools in babies

Black stools in babies are often observed in the first days after delivery. This first stool os called meconium, It is a dark green poop that is produced by the fetus while in-utero, and eliminated within the first hours of life. By the 6th day, the stool color may stool have some green or burgandy tinges. After a few weeks and months, baby stools will often change in color and textures. Poop will especially change with the introduction of new foods, like oatmeal, fruits, vegetables, meats and eggs. 

In some cases, baby stool may appear to have scant amounts of blood, however it is generally not a concern. It is usually a sign of a milk allergy or a cold virus. Nonetheless, you should still inform your doctor if you notice in red colors or new dark color changes in your baby’s stool. 

When to go to the doctor

You should see your doctor for assessment if you suspect that your stool contains blood. Other signs and symptoms that should be assessed include:

  • A new, intensely foul odor 
  • Severe abdominal pain 
  • Nausea and vomiting 
  • Bright red blood in the stool or vomit 
  • Weight loss 
  • Appetite changes 

The doctor will assess your symptoms and health history, and may order testing like a stool test or endoscopy. 

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Atualizado por Tua Saude editing team, em June de 2022. Clinical review por Dr. Antonio Carlos Moraes - Gastroenterologist, em March de 2022.

References

  • NHS. Bleeding from the bottom (rectal bleeding). Available on: <https://www.nhs.uk/conditions/bleeding-from-the-bottom-rectal-bleeding/>. Access in 07 Feb 2020
  • AMERICAN CANCER SOCIETY. Blood in Stool. Available on: <http://www.cancer.org/treatment/treatments-and-side-effects/physical-side-effects/stool-or-urine-changes/blood-in-stool.html>. Access in 07 Feb 2020
Show more references
  • GOLDMAN, Lee; SCHAFER, Andrew I.. Goldman-Cecil Medicina. 25.ed. Rio de Janeiro: Elsevier, 2018. 892-898.
Gastroenterologist
Gastroenterologist with specialization completed at the Federal University of Rio de Janeiro. Licensed to practice under the CRM-RJ #436069.