Black poop usually means one of two things: something you ate or swallowed changed the color, or blood from your upper digestive tract has been digested on its way through. The first is harmless. The second needs medical attention. Telling them apart is straightforward once you know what to look for.
Harmless Causes of Black Stool
Several common foods and medications turn stool black without any bleeding involved. Iron supplements are one of the most frequent culprits. Bismuth, the active ingredient in Pepto-Bismol, is another. Activated charcoal, black licorice, blueberries, and blood sausage can all do the same thing.
If one of these is responsible, your stool will be dark but otherwise normal in texture. It won’t be sticky or tarry, and it won’t have an unusually strong smell. The color change typically resolves within a day or two after you stop taking the supplement or eating the food in question.
What Digested Blood Looks Like
When bleeding occurs in the esophagus, stomach, or upper small intestine, the blood gets broken down as it travels through the rest of the digestive tract. By the time it reaches the toilet, it no longer looks red. Instead, it produces a distinctive type of stool that doctors call melena: jet black, sticky, tarry in texture, and notably foul-smelling. The odor is a byproduct of blood being digested, and it’s strong enough that most people notice it immediately.
That sticky, tar-like consistency is the clearest way to distinguish digested blood from a stool that’s simply been stained dark by food or medication. Color alone isn’t enough to tell the difference, but texture and smell are reliable clues. It takes roughly 50 milliliters of blood in the stomach (about 3 tablespoons) to turn stool black this way.
Common Medical Causes
About 90% of significant digestive bleeding originates above the point where the small intestine begins, in the esophagus, stomach, or duodenum. The most common causes include:
- Peptic ulcers: Open sores in the stomach lining or upper small intestine, often caused by a bacterial infection or long-term use of anti-inflammatory painkillers like ibuprofen or aspirin.
- Gastritis: Inflammation of the stomach lining, which can erode blood vessels near the surface.
- Esophageal varices: Swollen veins in the esophagus, typically linked to liver disease, that can rupture and bleed.
- Tears in the esophagus: Sometimes caused by forceful vomiting or retching.
In rare cases, if food moves slowly through the intestines, bleeding from further down the digestive tract (as far as the beginning of the large intestine) can also produce black, tarry stool. But this is uncommon. Most of the time, black tarry stool points to a problem higher up.
How to Tell If You Should Be Concerned
Start by thinking about what you’ve eaten or taken in the last day or two. If you recently took Pepto-Bismol, started an iron supplement, or ate a large serving of blueberries, that’s likely your answer. Watch for a return to normal color once you stop.
If you can’t trace the color to a food or medication, pay attention to the texture and smell. A tarry, sticky stool with a strong odor is a sign of bleeding and warrants prompt medical evaluation. You don’t need to wait for additional symptoms to act on this one.
Certain accompanying symptoms make the situation more urgent. Abdominal cramping or pain, feeling lightheaded or dizzy, or fainting suggest enough blood loss to affect your circulation. More severe signs include a fast heart rate, pale skin, cold hands and feet, confusion, and heavy sweating. These are symptoms of shock from significant blood loss and require emergency care immediately.
What Happens During Evaluation
If you seek care for black, tarry stool, the initial goal is figuring out whether blood is actually present and where it’s coming from. A simple stool test can detect hidden blood that isn’t visible to the eye. If bleeding is confirmed, the standard next step is an endoscopy, a procedure where a thin, flexible camera is passed through the mouth to examine the esophagus, stomach, and upper small intestine. This is typically done within 24 hours of arriving at the hospital.
For people whose risk turns out to be very low based on their symptoms and lab results, outpatient follow-up may be appropriate instead of hospitalization. Not every case of black stool from bleeding requires an emergency admission, but it does require evaluation to rule out something that could worsen.
Black Stool vs. Bright Red Blood
The color of blood in your stool tells you roughly where the bleeding is happening. Black, tarry stool generally means the source is in the upper digestive tract, because the blood has had time to be broken down during digestion. Bright red blood on toilet paper or in the bowl usually comes from the lower digestive tract: the colon, rectum, or anus. Hemorrhoids are a common and relatively benign cause of bright red bleeding.
Neither type should be ignored if it persists, but they point to different parts of the digestive system and different underlying causes. The distinction helps guide what kind of evaluation you’ll need.