Black stool has two main causes: something you ate or swallowed, or bleeding somewhere in your upper digestive tract. The difference between a harmless explanation and a serious one often comes down to texture, smell, and what else you’re feeling. Most people who notice black poop can trace it to a food, supplement, or medication, but it’s worth knowing what to look for.
What Harmless Black Stool Looks Like
Several common foods and over-the-counter products can turn your stool dark brown to black. Iron supplements are one of the most frequent culprits. Bismuth, the active ingredient in Pepto-Bismol and similar stomach medicines, reacts with tiny amounts of sulfur in your saliva and digestive system to form bismuth sulfide, a black-colored compound. This can darken both your tongue and your stool, and it’s completely harmless.
Black licorice, blueberries, blood sausage, and activated charcoal can all do the same thing. If you recently consumed any of these, the color change typically resolves within a day or two after you stop. The stool itself will look dark but otherwise normal in texture. It won’t be sticky or unusually foul-smelling.
When Black Stool Signals Bleeding
The medical term for black stool caused by bleeding is melena, and it looks and smells distinctly different from a food-related color change. Classic melena is jet black with a tarry, sticky consistency. It has a particularly strong, offensive odor that most people find unmistakable. That smell comes from blood being broken down as it travels through your digestive system. A smaller amount of bleeding may produce stool that looks more dark brown than true black, which can make it harder to distinguish from dietary causes.
Melena typically points to bleeding in the upper part of your digestive tract: the esophagus, stomach, or the first section of your small intestine. The blood turns black because stomach acid and digestive enzymes break it down during the hours it takes to move through your system. This is different from bright red blood in or on your stool, which usually means bleeding lower down, closer to the rectum.
Common upper GI sources include stomach ulcers (often from long-term use of anti-inflammatory painkillers like ibuprofen or naproxen), irritation of the stomach lining, and tears in the esophagus. Less commonly, bleeding can come from abnormal blood vessels or growths in the upper digestive tract.
How to Tell the Difference
Ask yourself three questions. First, have you taken Pepto-Bismol, iron supplements, or eaten any of the foods listed above in the past couple of days? If yes, that’s likely your answer. Stop taking or eating the suspect item and see if your stool returns to normal.
Second, what does the stool actually look like? Food and supplement-related darkening produces stool that’s dark but formed and normal in texture. Melena is sticky and tar-like, almost like roofing tar or thick motor oil. It clings to the bowl. If your stool has that sticky, tarry quality, that’s a more concerning sign regardless of what you’ve eaten recently.
Third, how do you feel otherwise? Black stool from bleeding rarely happens in isolation. Pay attention to lightheadedness or dizziness (especially when standing up), unusual fatigue, a racing heartbeat, abdominal pain, nausea, or vomiting that looks like coffee grounds. Any of these alongside black stool suggests active blood loss and needs prompt medical attention.
What Happens if You Go to the Doctor
If your doctor suspects bleeding, the first step is usually a stool test to confirm whether blood is actually present. A fecal immunochemical test can detect hidden blood that isn’t visible to the naked eye, and it’s more sensitive than older stool tests. It only tells your doctor whether blood is there or not. It can’t identify where the bleeding is coming from.
If blood is confirmed, the next step is typically an upper endoscopy, where a thin camera is passed through your mouth into your stomach and upper intestine to locate the source. This procedure both diagnoses and, in many cases, treats the bleeding at the same time.
Keep in mind that a negative stool test doesn’t always rule out a problem. Some bleeding is intermittent, meaning it can be present one day and absent the next. If your symptoms return or you continue noticing tarry black stools, that warrants follow-up even after a normal test result.
Black Stool in Newborns
If you’re a new parent noticing very dark stool in your baby’s diaper, this is almost certainly meconium, which is completely normal. Meconium is the thick, dark green to black substance that fills a baby’s intestines before birth. Babies typically pass it within 24 to 48 hours after delivery. Once your baby starts feeding on breast milk or formula, their digestive system pushes the remaining meconium out, and stool color gradually transitions to yellow or green over the following days. Black stool in a newborn only becomes a concern if it persists beyond the first few days of life or reappears after stools have already lightened.
The Bottom Line on Timing
If you can connect your black stool to a specific food, supplement, or medication, give it 48 to 72 hours after stopping that item. Your stool color should return to its usual brown. If it doesn’t, or if you never had an obvious dietary explanation to begin with, that’s worth a call to your doctor. If the stool is tarry and sticky, has a notably foul smell, or you’re experiencing dizziness, weakness, or abdominal pain alongside it, don’t wait. Those symptoms together suggest enough blood loss to need evaluation the same day.