Black poop usually means you ate something that changed the color, like blueberries, black licorice, or iron supplements. But if your stool is black, tarry, and sticky with a strong foul smell, it could signal bleeding in your upper digestive tract, which needs medical attention. The key is knowing which type you’re dealing with.
Common Foods and Medications That Turn Stool Black
Several everyday foods and over-the-counter products can darken your stool enough to make it look black. The most common culprits include blueberries, black licorice, blood sausage, iron supplements, and activated charcoal. Bismuth-based medications like Pepto-Bismol are another frequent cause. When bismuth meets the small amounts of sulfur naturally present in your saliva and digestive system, they combine to form bismuth sulfide, a black substance. This is completely harmless and clears up once you stop taking the medication. You might also notice your tongue turning black for the same reason.
With all of these causes, your stool may look dark or black, but it will have a normal texture and smell. That distinction matters a lot.
How to Tell Harmless Black Stool From a Warning Sign
The medical term for black stool caused by bleeding is melena, and it looks and smells distinctly different from stool that’s simply been stained by food or medication. Classic melena is jet black with a tarry, sticky consistency, almost like roofing tar. It also has a particularly strong, offensive odor that’s hard to miss. That smell comes from blood being broken down and digested as it travels through your gut. The longer the blood has been in your system, the darker and more foul-smelling the stool becomes.
Stool that’s been darkened by blueberries or iron pills won’t have that sticky tar-like texture or that distinctive smell. If you recently ate one of the foods listed above or started a new supplement, that’s very likely the explanation. If you haven’t changed your diet or medications and the stool is tarry and unusually foul, that’s a different situation.
It’s also worth noting that a small amount of bleeding may look more dark brown than truly black, and some conditions that cause upper digestive bleeding can also cause diarrhea, making the stool wetter than the classic tarry description.
Why Bleeding Turns Stool Black
When bleeding happens in the upper part of your digestive tract (your esophagus, stomach, or the first section of your small intestine), the blood doesn’t stay red. Stomach acid chemically changes the hemoglobin in blood through oxidation, converting it from red to a dark brown or black substance. By the time that digested blood works its way through the rest of your intestines and comes out, it gives stool its characteristic black, tarry appearance. This is why black stool specifically points to upper digestive bleeding, while bleeding lower in the intestines or colon typically produces red or maroon-colored stool instead.
Medical Conditions That Cause Melena
The most common cause of upper digestive bleeding is peptic ulcers, which are open sores in the lining of the stomach or the upper part of the small intestine. These are often caused by a bacterial infection or long-term use of anti-inflammatory painkillers like ibuprofen or aspirin.
Other conditions that can cause black, tarry stools include gastritis (inflammation of the stomach lining), esophageal varices (swollen veins in the esophagus, often related to liver disease), and tears in the esophagus from severe vomiting. Tumors in the stomach or upper intestine can also bleed slowly enough to produce melena without other obvious symptoms.
Symptoms That Signal an Emergency
Black tarry stools on their own warrant a call to your doctor, but certain accompanying symptoms mean the bleeding may be significant. Feeling dizzy or lightheaded, fainting, a rapid heartbeat, unusual fatigue or weakness, vomiting material that looks like dark coffee grounds, and pale or clammy skin all suggest enough blood loss to affect your circulation. If you’re experiencing any of these alongside black stool, seek emergency care rather than waiting for a scheduled appointment.
What Happens When You Get Checked Out
If your doctor suspects your black stool contains blood, the first step is usually a stool test that detects hidden (occult) blood not visible to the naked eye. This simple test can confirm whether blood is actually present or whether the color change is harmless.
If blood is found, the next step is typically an upper endoscopy, where a thin flexible camera is passed through your mouth to examine your esophagus, stomach, and upper small intestine directly. This lets doctors both find and often treat the source of bleeding in the same procedure. If upper endoscopy doesn’t reveal the source, a colonoscopy may follow. In the uncommon situation where both come back normal, a capsule endoscopy (swallowing a tiny camera in pill form) can examine the middle sections of the small intestine that are harder to reach with standard scopes.
For most people who search this question, the answer turns out to be something they ate or a supplement they’re taking. A quick mental inventory of what you’ve consumed in the past day or two is the simplest first step. If nothing obvious comes to mind and the stool is sticky, tarry, or foul-smelling, that’s when it’s worth getting checked.