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What causes black stools? 20 possible conditions

What Are Bloody or Tarry Stools?

Bloody or tarry stools refer to a stool sample that is either dark red or black in color. Bloody or tarry stools can indicate bleeding or other injuries in your gastrointestinal tract. You may also have dark, discolored bowel movements after eating dark-colored foods. Notify your doctor any time you have bloody or black-colored stool to rule out serious medical conditions.

Medical Causes of Black, Tarry Stools

Bleeding in the upper portion of your digestive system can cause black, tarry stools. Ulcers or another form of irritation in your esophagus or stomach known as gastritis can cause bleeding. When the blood mixes with digestive fluids, it takes on the appearance of tar.

Certain medications can also lead to black-colored stools. Iron supplements and bismuth-based medications, for example, can darken your stools.

Sometimes, serious blood and circulation abnormalities in your digestive system can cause black, tarry stools. These include:

  • bowel ischemia: a reduction of blood flow to the intestines
  • vascular malformation: misshapen veins
  • varices: large protruding veins in the intestines

Medical Causes of Red, Bloody Stools

Red or bloody stools can also be caused by several different medical conditions. Your stools may be bloody due to bleeding in the lower half of your digestive system. Cancerous or benign polyps on your colon can produce gastrointestinal bleeding in some cases. Inflammatory bowel diseases such as diverticulosis, ulcerative colitis, and Crohn’s disease may cause you to expel bright red or maroon-colored blood in your stool.

A common cause of blood stools is the presence of hemorrhoids. Hemorrhoids are swollen veins located in your rectum or anus. Straining to produce a bowel movement can cause bleeding.

Blockages at any point in your digestive tract can cause black, tarry, or bloody stools.

Dietary Causes of Bloody- or Tarry-Looking Stools

The foods you eat can cause your stools to appear bloody or tarry. Eating red or black foods can give your feces a dark appearance without the existence of blood. Black licorice, blueberries, dark chocolate cookies, red-colored gelatin, beets, or red fruit punch are all examples of foods that can discolor your bowel movements.

What to Expect at the Doctor’s Office

Your doctor will take a medical history and perform a physical examination to determine the cause of your unusual stool color. Imaging tests such as MRIs, X-rays, and CT scans can help your doctor see the blood flow to your digestive system. These diagnostic tools will reveal any blockages that could be causing gastrointestinal (GI) bleeding.

Your doctor may schedule a colonoscopy to assess the condition of your colon. A colonoscopy is often performed under sedation. Your doctor will use a thin, flexible tube with a camera on the end to see the inside of your colon and look for the cause of your symptoms.

Treatment and Management of Bloody or Tarry Stools

Treatment of bloody or tarry stools varies according to the cause of the problem. According to the American Cancer Society, people that have hemorrhoids can ease the passage of stool and reduce bleeding by using stool softeners under a doctor’s direction (ACS). Sitz baths can also ease the pain of hemorrhoids and prevent bleeding.

Your doctor may prescribe acid-reducing medications to treat bleeding ulcers, or antibiotics and immunosuppressant drugs to calm inflammatory bowel disease and infections.

Vein abnormalities and blockages may require surgical repair if the bleeding does not stop on its own. If you have lost a lot of blood through your stool, you may be at risk for developing anemia. You may need a blood transfusion to replenish your supply of red blood cells.

Polyps on your colon that cause bloody stools can indicate precancerous conditions or cancer in some people. Your doctor will determine the appropriate treatment for these conditions. Removal of the polyps may be all that is needed in some cases. Others may require radiation therapy and chemotherapy if cancer is present.

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See a list of possible causes in order from the most common to the least.


Bleeding Esophageal Varices

This condition is considered a medical emergency. Urgent care may be required.

Bleeding esophageal varices occur when swollen veins in your lower esophagus rupture and bleed due to excess pressure. This condition is a medical emergency and must be dealt with promptly.

Read more »


Stomach Ulcer

Stomach ulcers are painful sores in the stomach lining or small intestine. They occur when the mucus that protects the stomach from digestive juices is reduced.

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Peptic Ulcer

Peptic ulcers are painful sores in the lining of the stomach, esophagus, or small intestine. Peptic ulcers are a fairly common health problem.

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Transfusion Reactions

A transfusion reaction is a rare condition that occurs when a person receives a transfusion with blood that is not matched to their blood type. This may cause symptoms such as back pain, fever, fainting, or dizziness.

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Necrotizing Enterocolitis

This condition is considered a medical emergency. Urgent care may be required.

Necrotizing enterocolitis is inflammation and death of intestinal tissue. It may involve just the lining or the entire thickness of the intestine. This very dangerous disease is most common in premature infants.

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Colorectal (Colon) Cancer

Colorectal cancer is a cancer that originates in the rectum or colon. Both of these organs are located at the lower portion of your digestive system. The colon is at the end of the large intestine and the rectum is a...

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Colonic (Colorectal) Polyps

Colonic polyps are growths that appear on the surface of the large intestine. A person may have more than one polyp, and they may be flat or raised, benign or cancerous.

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Stomach Cancer (Gastric Adenocarcinoma)

Stomach cancer occurs when cancerous cells form in the stomach lining. Because it's difficult to detect, it's often not diagnosed until it's more advanced.

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Colitis is inflammation of the colon, often causing discomfort and pain in the abdomen, as well as other gastrointestinal symptoms. Colitis has many possible causes, which determine the type.

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This condition is considered a medical emergency. Urgent care may be required.

Most common in boys, intussusception occurs when a portion of the intestines become enfolded, causing a blockage. Symptoms include abdominal pain, vomiting, bloody stools, and others. It is potentially life-threatening.

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Crohn’s Disease

Crohn's disease is a chronic bowel disease that causes severe inflammation of the digestive tract. It is associated with abdominal pain, diarrhea, and may affect your quality of life. Crohn's disease is characterized b...

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Diverticula are bulging sacs that can appear in the lining of your large intestine. Diverticulitis occurs when these sacs get acutely infected or inflamed.

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Weakness in your stomach lining allows digestive juices to damage and inflame it, causing gastritis. It comes in both acute and chronic forms.

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Alcoholic Liver Disease

Damage to the liver from excessive drinking can lead to ALD. Years of alcohol abuse cause the liver to become inflamed and swollen. This damage can also cause scarring known as cirrhosis. Cirrhosis is the final stage o...

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Acquired Platelet Function Disorder

Platelets are a type of blood cell. They play an important role in healing from injuries. Platelets help your body to form blood clots and stop bleeding. Some people’s platelets don’t function the way the...

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Enteritis is the inflammation of your small intestine. In some cases, the inflammation includes the stomach and large intestine. Ingesting food and water contaminated with bacteria is a leading cause of enteritis...

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Esophageal Cancer

Esophageal cancer occurs when a malignant (cancerous) tumor forms in the lining of the esophagus, which is the muscular tube responsible for moving food from the throat to the stomach. As the cancer grows, it can affec...

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This condition is considered a medical emergency. Urgent care may be required.

Anthrax is a serious illness caused by a microbe that lives in soil, called Bacillus anthracis. Inhalation may result in cold and flu symptoms; signs of ingestion include nausea and abdominal pain.

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Acute Gastritis

Acute gastritis is a sudden inflammation or swelling in the lining of the stomach. It causes severe and nagging pain. Fortunately, the pain usually only lasts for a short time. Acute...

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Hypersensitivity (Allergic) Vasculitis

Vasculitis is inflammation of blood vessels. It can damage blood vessels by thickening, scarring, and weakening the cell wells. There are many different types of vasculitis; some are acute and last a short time, whil...

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.