What Are the Causes of Black Stool?

Black stool can be caused by eating certain foods, taking certain medications or supplements (like iron), or it can be the result of something more serious. Stool is also known as bowel movements, feces, or poop, and bodily waste left over after digestion.

See a doctor if you have a history of gastrointestinal (GI) bleeding, your stool has an especially foul smell, or the problem lasts longer than a few days.

This article explores the symptoms and causes of black stool.

Food and Supplements

Black stools could be caused by food, supplements, medication, or minerals. Iron supplements, taken alone or as part of a multivitamin for iron-deficiency anemia, may cause black stools or even green stools.

Foods that are dark blue, black, or green may also cause black stools. Substances that are often found to cause black stools include:

• Black licorice
• Blueberries
• Iron supplements
• Lead
• Bismuth subsalicylate (Pepto-Bismol)

If you're seeing black stools and can trace it back to a food you ate, that's OK. However, you should consult with a doctor immediately if black stools cannot be traced back to a food, an iron supplement, or Pepto-Bismol.

If there's no obvious reason for a black stool, it could be time to look for blood in the stool. A variety of medical reasons can cause black stools that are also tarry with a foul smell.

Blood in the Stool (Melena)

Blood that comes from the upper GI tract—such as the esophagus or the stomach—may turn the stool black. This is a condition called melena. If you have melena, you may also notice that your stool has a tarry texture or is similar to coffee grounds.

As the blood passes through the body and interacts with enzymes in the digestive process, the blood changes from red to black. This makes it a bit more difficult to tell if there is red blood in or on the stool.

Bright red blood in or on the stool is typically blood from the lower GI tract, such as the rectum or the colon. This is a condition called hematochezia. Blood stemming from this region will be more red in appearance, because it will be exposed to less of the digestive process.

Some people may have a known risk factor for bleeding in the GI tract. Talk to a doctor about the potential for bleeding and blood in the stool if any of these potential risk factors apply to you:

• Liver disease
• Cancer
• Dieulafoy lesion (a rare condition of the stomach)
• Erosive esophagitis (inflammation in the esophagus)
• Erosive gastritis (inflammation in the stomach)
• Intestinal ischemia (blood supply to the intestines is cut off)
• Peptic ulcers (sores in the stomach lining or upper part of small intestine)
• Tear in the esophagus (Mallory-Weiss tear)
• Varices (abnormally large veins) in the esophagus or stomach

Diagnosis

The black color alone is not enough to determine whether or not there is blood in the stool. Remember, it could be caused by food or iron supplements. Therefore, a doctor will need to confirm if there is blood, which may require various tests.

Your doctor may have you collect a small stool sample at home using a special kit, which is then sent to a lab for evaluation.

If you are diagnosed with melena, a physician may order further diagnostic tests to determine the cause and the exact location of the bleeding.

In particular, your healthcare provider may conduct an esophagogastroduodenoscopy (EGD, or upper endoscopy). This procedure involves inserting a flexible tube with a camera down your throat so that your doctor can inspect the lining of the esophagus, stomach, and upper intestine.

Causes of Blood in Stool

Stool that is visibly black and tarry typically indicates the presence of an acute condition in the upper GI tract. After the bleeding has stopped, stool may continue to appear black and tarry for several days.

Possible causes of melena include a bleeding ulcer, gastritis, esophageal varices (enlarged veins), or a tear in the esophagus from violent vomiting (Mallory-Weiss tear).

Ulcer

An ulcer is a type of sore on the lining of the stomach that can cause bleeding and result in melena. Contrary to popular belief, stomach ulcers are not usually caused by stress or spicy food, although these can aggravate an already existing ulcer.

In fact, stomach ulcers are usually caused by an infection with bacteria called Helicobacter pylori (H. pylori). Your doctor may prescribe antibiotics to eliminate the infection. Your doctor may also recommend an acid reducer.

Long-term use of pain medications, known as nonsteroidal anti-inflammatory drugs (NSAIDs), are another cause of stomach ulcers. NSAIDs include common over-the-counter drugs, such as ibuprofen, naproxen sodium, and aspirin. Some NSAIDs are prescribed by physicians.

NSAIDs can irritate the stomach by weakening the lining's ability to resist acid made in the stomach. For this same reason, NSAIDs have an adverse effect on Crohn's disease and ulcerative colitis—conditions that cause ulcers and inflammation of the GI tract.

Stomach ulcers caused by NSAIDs usually heal after the offending drug is discontinued.

Gastritis

Gastritis is inflammation of the stomach lining. This inflammation can be caused by too much alcohol, eating spicy foods, smoking, infection with bacteria, or by the prolonged use of NSAIDs. Gastritis can also develop after surgery or trauma, or it may be associated with already existing medical conditions.

Gastritis that is left untreated can lead to stomach ulcers and other complications. Some people have no symptoms, while acute, suddenly occurring cases of gastritis may only result in tarry, black stool.

Persistent bleeding can lead to more severe symptoms like:

• Abdominal pain
• Lightheadedness
• Nausea
• Vomiting
• Indigestion

If your doctor suspects gastritis, they may prescribe antacids or proton pump inhibitors, antibiotics that treat H. pylori infection, or sucralfate—a drug that helps the stomach heal by soothing irritation.

If these treatments fail to resolve your symptoms, your doctor may order an upper endoscopy to take a closer look at your stomach and small intestine.

Esophageal Varices

Esophageal varices are enlarged veins in the wall of the lower esophagus or upper stomach. When these veins rupture, they may cause bleeding and lead to blood in the stool or in vomit.

Esophageal varices are serious complications resulting from high blood pressure brought on by cirrhosis of the liver.

Most people with esophageal varices experience no symptoms unless the veins rupture. Symptoms of bleeding esophageal varices include:

• Melena
• Vomiting blood
• Lightheadedness
• Fainting

These symptoms warrant immediate medical attention, as bleeding esophageal varices are life-threatening.

Mallory-Weiss Tear

This is a tear in the mucous membrane that joins the esophagus and the stomach. If this tear bleeds, it can result in melena.

This condition is fairly rare. It only only occurs in about seven out of 100,000 people in the US and may be caused by violent vomiting, coughing, or epileptic convulsions. About 5% of people with a Mallory-Weiss tear do not survive.

Like other conditions that cause melena, symptoms of a Mallory-Weiss tear may not be obvious. Along with tarry, black stool, some people may experience any of the following:

• Vomiting tarry blood
• Lightheadedness
• Shortness of breath
• Diarrhea
• Abdominal pain
• Chest pain

For most people, the tear will heal on its own. If it does not resolve itself, you may need endoscopic treatment to seal the lesion. This may either take the form of a medication that is injected internally, or a type of heat therapy known as electrocoagulation.

Summary

Stool that appears black is not always a sign of a bigger health problem. Your stool can look black as a result of food or iron supplements you have eaten. If that's the case, the color will return to normal within a day or so.

If it doesn't, and if you cannot trace it back to something you have eaten, ask yourself:

• Does the stool have a tarry appearance, somewhat like coffee grounds?
• Is there an especially foul smell that has not gone away?
• Does my medical history place me at risk for gastrointestinal bleeding?

If you answered yes to one or more of these questions, or if you are experiencing symptoms like nausea, vomiting, or lightheadedness, you should contact your healthcare provider.

A Word From Verywell

Though it may be surprising to see, occasional black stool is not something to worry about so long as it occurs after you eat dark-colored foods or take an iron supplement.

That said, if black or tarry stools cannot be attributed to something you have consumed, or you simply feel like something is off, it's best to get checked out. Some of the conditions that cause GI bleeding can be life-threatening unless treated promptly.