Black poop has two very different explanations: something you ate or swallowed, or bleeding in your upper digestive tract. The difference matters, and fortunately it’s usually possible to tell the two apart based on texture, smell, and what else is going on in your body.
The Most Common Harmless Causes
Several everyday foods and over-the-counter products can turn your stool noticeably dark or black. Iron supplements are one of the most frequent culprits. Bismuth-based stomach medications like Pepto-Bismol do the same thing. Activated charcoal, black licorice, blueberries, and blood sausage can all darken stool color as well.
If iron supplements or bismuth are the cause, your stool typically returns to its normal color within one to two days after you stop taking them. The color change in these cases is purely cosmetic. Your stool may look darker, but it won’t have a distinctly foul odor or a sticky, tar-like consistency. That distinction is important.
What Bleeding in the Digestive Tract Looks Like
When black stool comes from blood, it looks and smells different from stool that’s simply been stained by food or supplements. Blood that originates high up in the digestive tract, such as the stomach or upper small intestine, gets partially digested as it travels through. Stomach acid and digestive enzymes break down the hemoglobin in red blood cells, turning it jet black by the time it reaches the colon.
The medical term for this is melena, and it has a very recognizable profile: jet black color, a tarry or sticky consistency that can almost resemble roofing tar, and a distinctly strong, offensive smell that’s noticeably different from normal stool. If your black stool looks firm and formed, doesn’t stick, and doesn’t smell unusually foul, it’s far more likely to be dietary.
Medical Conditions That Cause Black Stool
The most common cause of true melena is a peptic ulcer, an open sore in the lining of your stomach or the first section of your small intestine. These ulcers can slowly ooze blood, sometimes without causing much abdominal pain. Long-term use of anti-inflammatory pain relievers like ibuprofen or aspirin increases ulcer risk significantly.
Erosive gastritis, where the stomach lining becomes inflamed and worn down, can also produce enough bleeding to darken stool. This is often related to the same medications, heavy alcohol use, or bacterial infection.
A less common but more serious cause involves swollen veins in the esophagus, which develop when liver disease creates a backup of blood pressure in the portal vein. Blood gets rerouted through smaller veins in the lower esophagus that aren’t built to handle the volume. These thin-walled veins balloon outward and can leak or rupture, sometimes causing life-threatening bleeding. Black, tarry stool is one of the warning signs.
How to Tell If Blood Is Present
You can’t always tell by looking. If there’s any uncertainty, a simple stool test can confirm whether blood is present. The most widely used version, called a fecal immunochemical test (FIT), detects blood with about 87% sensitivity and 85% specificity. That means it catches most cases of hidden bleeding while producing relatively few false alarms. Your doctor can run this test quickly using a small stool sample.
An older version of this test, which uses a chemical reaction rather than antibodies, is somewhat less sensitive (around 68%) but still useful as a screening tool. Either way, the test removes the guesswork.
Symptoms That Signal an Emergency
Black, tarry stool on its own warrants a call to your doctor. But certain accompanying symptoms suggest active, significant bleeding and call for more urgent attention:
- Lightheadedness or feeling faint, especially when standing up, which can indicate meaningful blood loss
- Rapid heartbeat even at rest
- Vomiting blood or material that looks like coffee grounds
- Severe abdominal pain
- Cold, clammy skin or visible paleness
Any combination of these with black stool points to upper GI bleeding that may need immediate treatment.
Black Stool in Newborns
If you’re a new parent, seeing black stool in your baby’s diaper during the first few days of life is completely normal. This is meconium, a greenish-black, tar-like substance made up of everything your baby swallowed in the womb: amniotic fluid, mucus, bile, and shed cells. It typically passes within the first two to three days.
After those first few days, black stool in an infant should not reappear. If it does, it may indicate blood entering your baby’s gastrointestinal tract, which needs medical evaluation.
What to Do Next
Start by thinking about what you’ve eaten or taken in the past 48 hours. If you’re on iron supplements, bismuth medications, or recently ate a large amount of blueberries or black licorice, give it a day or two after stopping and see if the color normalizes. If it does, that was almost certainly the cause.
If you can’t explain the color, or if the stool is sticky, tar-like, and unusually foul-smelling, that pattern points toward digested blood. A stool test can confirm it, and your doctor will likely want to look at the upper digestive tract with an endoscopy to find the source. Most causes of upper GI bleeding are treatable, especially when caught before significant blood loss occurs.