14 Known Causes of Dark Stool

2. Dark-Colored Foods

Some foods can make your stool look dark without causing harm. These color changes often come from strong natural or added dyes that pass through your body. You may notice this after eating foods with deep blue, purple, red, or black color. The stool can look dark brown, greenish-black, or even near black. The color change usually fades within a day or two.

Foods commonly linked to darker stool include black licorice, blueberries and blackberries, beets and beet‑based foods, blood sausage, and foods with dark food coloring, such as certain candies or drinks. Charcoal-infused foods can also darken stool. These products have become more common in baked goods and drinks.

Smell and texture usually stay normal with food-related changes. You may not have pain, weakness, or other symptoms. That pattern helps separate food causes from health problems.

Looking at timing can help clarify the source. If dark stool appears soon after eating these foods and then clears, food is a likely cause. If the color lasts, looks tar-like, or comes with dizziness or stomach pain, the cause may not be food.

3. Medicines Containing Bismuth

Some antidiarrheal agents contain bismuth. When you take these medicines, you may notice dark or black stool. This change often looks sudden and can feel alarming.

Bismuth reacts with small amounts of sulfur in your saliva and digestive system. This reaction creates a dark substance that passes through your gut. As it leaves your body, it can turn your stool black or very dark green.

This color change does not mean bleeding in most cases. You may also notice a dark coating on your tongue. Both changes are harmless and usually fade a few days after you stop the medicine.

You often take these antidiarrheal agents for diarrhea, upset stomach, nausea, or heartburn. You usually use them for short periods. Using them longer than directed can increase side effects, including darker stool. Dark stool from bismuth differs from stool caused by bleeding. Bleeding often creates a sticky, tar-like texture and a strong smell.

4. Bleeding Ulcer

A bleeding ulcer forms when an open sore in your stomach or upper small intestine starts to bleed. This bleeding can turn your stool dark, sticky, and tar-like. The color changes because blood breaks down as it moves through your digestive system. You may notice other signs along with dark stool. These can include stomach pain, nausea, weakness, or feeling lightheaded. Some people also vomit material that looks dark or grainy.

Several factors can raise your risk. Long-term use of anti-inflammatory pain relievers can damage the stomach lining. Infection with certain bacteria can also weaken the lining and allow an ulcer to form.

Alcohol use and smoking can make ulcers worse. Stress alone does not cause ulcers, but it can slow healing. Poor eating habits may add irritation but usually do not start the problem by themselves. Bleeding from an ulcer can be slow or sudden. Slow bleeding may cause dark stool over days or weeks, while a faster bleeding can lead to more severe symptoms in a short time.

5. Esophageal Cancer

Esophageal cancer starts in the esophagus, the tube that carries food from your mouth to your stomach. It can cause dark stool when bleeding happens in the upper digestive tract. Your body digests this blood, which can turn stool black and sticky. You may not notice symptoms at first. As the disease grows, it can bleed slowly over time. This slow bleeding often leads to dark stool with a strong smell rather than bright red blood.

Other signs can appear as the cancer affects how food moves. You might feel food stick in your chest or have trouble swallowing. Heartburn, chest pain, or vomiting can also occur, even when you are not eating.

Certain risks raise your chance of this cancer. Smoking, heavy alcohol use, long-term acid reflux, and a condition where acid damages the esophagus lining can all play a role. Being male and older also increases risk. Dark stool linked to this condition often appears with other changes like weight loss, low energy, or feeling full quickly. Stool tests may identify blood traces even when you cannot see it.

6. Gastric Cancers

Gastric cancers start in the lining of your stomach. These cancers can cause dark stool when bleeding happens inside the stomach. The blood mixes with stomach acid, which turns it black and sticky by the time it passes out of your body.

You may not notice clear warning signs at first. Early symptoms often feel like common stomach problems. As the disease grows, bleeding becomes more likely, and dark stool may appear more often.

Dark stool linked to gastric cancers often appears very dark or black, has a sticky or tar‑like texture, and carries a strong, foul smell. This type of stool usually points to bleeding higher in the digestive tract. Unlike bright red blood, fresh blood is not visible because digestion alters its color before it leaves the body.

Other signs can appear along with dark stool. You may feel full after eating small amounts or lose weight without trying. Nausea, vomiting, or trouble swallowing can also occur as the stomach lining becomes damaged.

7. Mallory Weiss Tear

A Mallory Weiss tear is a small cut near the point where your food tube meets your stomach. This cut can bleed and cause dark, sticky stool. Dark stool forms when blood mixes with stomach fluids and moves through your gut.

You often develop this tear after strong or repeated vomiting. Long bouts of coughing can also cause it. You may notice other signs along with dark stool. These can include vomiting blood, feeling weak, or feeling lightheaded. The blood may look bright red when you vomit, but it often turns dark by the time it reaches your stool.

Most tears heal on their own within a few days. Doctors may use a camera test to find the tear if bleeding continues. During this test, they can stop bleeding with small tools if needed. You may receive acid-reducing medicines for a short time. These medicines lower stomach acid and help the area heal.

8. Esophageal Varices

Esophageal varices are swollen veins in your food pipe. They form when blood has trouble flowing through your liver and backs up into nearby veins. This pressure makes the veins stretch and weaken. If one breaks, it can bleed into your digestive tract. That bleeding can turn your stool dark, black, or tar-like.

You may not notice any signs at first. Small bleeding can change stool color without pain. Larger bleeding can cause vomiting blood, feeling dizzy, or looking pale. Long-term liver disease causes most cases. Scarring in the liver blocks normal blood flow. Alcohol-related liver damage and fatty liver disease are common reasons.

Dark stool happens because blood mixes with stomach acids. This process darkens the blood as it moves through your gut. By the time it reaches your stool, it often looks black and sticky. Doctors often find varices with a camera test that looks inside your throat and stomach. This test can also treat the veins by tying them off to stop bleeding.

9. NSAID Usage

Nonsteroidal anti-inflammatory drugs (NSAID) can cause dark stool when they irritate the lining of your stomach or upper gut. This irritation can lead to small cuts or sores that bleed. When blood mixes with stomach acid and moves through your digestive system, it can turn stool dark or black.

You may not feel pain right away. Bleeding can start slowly, even with short-term use. The risk rises if you take higher doses or use these drugs often. Dark stool linked to this drug class often looks black, sticky, or tar-like. It may also have a strong smell. These changes suggest bleeding higher in your digestive tract, not from the lower bowel.

You may also notice other signs along with dark stool. These can include stomach pain, nausea, weakness, or feeling lightheaded. Some people only notice the stool change and nothing else. Over-the-counter access makes these drugs easy to use, but that also increases risk. You might take them longer than planned without noticing harm.

10. Gastritis

Gastritis is inflammation of your stomach lining, which can bleed and turn your stool dark, black, or tar-like. As blood moves through your digestive system, it changes color and darkens your stool. You may not notice symptoms at first, and bleeding can happen slowly and without pain.

Common causes of gastritis include infection from stomach bacteria, regular use of anti‑inflammatory pain relievers, heavy alcohol use, and severe illness, injury, or major physical stress.

In some cases, your immune system mistakenly attacks the stomach lining. Less commonly, bile flowing back into the stomach irritates the tissue and leads to inflammation and bleeding. Dark stool linked to gastritis often appears with other signs such as stomach pain, nausea, vomiting, or poor appetite. If bleeding increases, you might feel weak or dizzy due to blood loss.

Treatment depends on the cause of the inflammation. Doctors focus on lowering stomach acid and allowing the lining to heal. If an infection causes the problem, treatment targets the infection while also protecting the stomach.

11. Benign Tumors

Benign tumors are noncancerous growths that can form in your digestive tract and affect how your stool looks. Some benign tumors in the stomach or upper small intestine bleed slowly over time, and blood moving through your digestive system can turn your stool black or tar-like. Many benign tumors cause no clear symptoms at first, and dark stool may be one of the few signs that something is wrong.

Common types that can lead to dark stool include growths such as polyps or other noncancerous tissue changes. These growths can rub against food and stomach acid, which causes small amounts of bleeding. You may notice additional changes along with dark stool, including a strong or foul stool odor, mild stomach discomfort, or feeling full sooner than usual.

12. Colitis

Colitis is swelling and irritation of the lining of your large intestine that can damage the surface and lead to bleeding. When bleeding moves slowly through your gut, it can darken before you pass it. This turns your stool dark brown, maroon, or almost black. The color often depends on how much blood is present and how long it stays in your body.

You may also notice loose stools, belly pain, or a strong urge to use the bathroom. Some people see mucus mixed with stool. These signs may flare up during active periods of the condition.

Several types of colitis exist, including long-term immune-related forms, short-term infections, and reduced blood flow to the colon. Each type can irritate the bowel and raise the chance of bleeding. Treatment focuses on calming inflammation and allowing the colon to heal. Doctors may use anti-inflammatory or immune-calming drug classes, and severe cases may require hospital care.

13. Colon Polyps

Colon polyps are small growths that form on the inside of your large intestine, often appearing during routine exams and usually not causing pain. Some colon polyps can bleed, and when bleeding happens slowly, your stool can turn dark brown or black as blood mixes with stool moving through your gut.

You may not notice other signs at first, but some people see blood on toilet paper, in the toilet, or on underwear. Others have bowel changes such as diarrhea or constipation lasting more than a week.

Not all polyps bleed, but flat polyps can still leak small amounts of blood over time, which makes dark stool more likely than bright red blood. Doctors often find polyps during a scope exam of the colon and usually remove them during the same procedure.

14. Foreign Objects or Trauma

Swallowing a foreign object or experiencing injury to your digestive tract can lead to dark stool. Sharp items, hard food pieces, or accidentally swallowed objects can scrape or cut tissue as they move through your body. Bleeding higher up in the digestive tract can darken your stool by the time it passes.

Physical trauma can also play a role. A hard hit to your abdomen, a fall, or forceful vomiting can injure the lining of your throat or stomach. Small tears may bleed slowly, which darkens your stool over time. You may not feel pain right away, which can delay noticing the cause.

Dark stool from injury often looks tar-like and smells strong. Your body digests the blood as it moves through your system, causing this color change. You might also notice symptoms such as stomach pain, nausea, or feeling lightheaded. Ongoing dark stool after trauma or a known swallowing incident signals active bleeding inside your body.