Black poop is not always a sign of something dangerous, but it can be. The answer depends almost entirely on the texture, smell, and what you’ve recently eaten or taken. In many cases, a food or supplement is the simple explanation. But black stool that is tarry, sticky, and unusually foul-smelling can signal bleeding in the upper digestive tract, which needs prompt medical attention.
Harmless Causes of Black Stool
Several common foods and over-the-counter products can turn your stool black without any bleeding involved. The most frequent culprits are iron supplements, bismuth-based stomach remedies (like Pepto-Bismol), activated charcoal, black licorice, blueberries, and blood sausage.
Iron supplements are probably the most common cause. When you take more iron than your body can absorb, the excess passes through your gut and darkens the stool. A European food safety review found that black stools reflect large amounts of unabsorbed iron in the gut and that the effect tends to show up at supplemental doses above about 25 mg per day. If your total daily iron intake stays around 40 mg or below (from food and supplements combined), black stools are less likely to occur.
Bismuth, the active ingredient in several over-the-counter stomach and diarrhea medicines, can also darken your stool to a grayish black and even turn your tongue dark. According to the Mayo Clinic, this is temporary and resolves once you stop taking the product. In both of these cases, the color change is cosmetic and harmless.
How to Tell if It’s Blood
The critical distinction is between stool that’s simply stained dark and stool that contains digested blood. When blood from the stomach, esophagus, or upper intestine travels through the digestive tract, it gets broken down and turns the stool a distinctive jet black. This is called melena, and it looks and feels very different from food-stained poop.
Classic melena has three hallmarks: it is jet black, it has a tarry or sticky consistency (think the texture of roofing tar), and it has an unusually strong, offensive odor that’s noticeably worse than normal stool. That smell comes from blood being digested as it moves through your intestines. If your stool is simply dark from blueberries or iron pills, it won’t have that same sticky texture or that distinctive foul smell.
This texture-and-odor check is a practical first step you can do at home. Formed, solid stool that’s dark but otherwise normal in texture is almost always from something you ate or took. Loose, sticky, tar-like stool with a terrible smell is a red flag.
What Causes Bloody Black Stool
When black stool does contain blood, the source is typically somewhere in the upper digestive tract: the esophagus, stomach, or the first part of the small intestine. The most common causes include stomach ulcers (peptic ulcers), inflammation of the stomach lining (gastritis), and swollen veins in the esophagus that can occur with liver disease. Less commonly, tumors in the stomach or upper intestine can bleed slowly enough to produce melena without other obvious symptoms.
The key point is that the bleeding has to travel a significant distance through the gut to turn black. Bleeding from the lower intestine or rectum typically shows up as bright red or maroon-colored blood instead. So black, tarry stool specifically points to a problem higher up in the digestive system.
Symptoms That Signal an Emergency
Black, tarry stool on its own warrants a call to your doctor. But certain accompanying symptoms suggest you may be losing blood fast enough to need emergency care:
- Dizziness or lightheadedness, especially when standing up, which can indicate dropping blood pressure from blood loss
- Rapid heartbeat or feeling your heart pounding, as your body tries to compensate for less blood volume
- Unusual fatigue or weakness that comes on suddenly
- Vomiting blood or material that looks like coffee grounds
- Abdominal pain, particularly in the upper stomach area
Any combination of tarry black stool with these symptoms points to active upper gastrointestinal bleeding. This is a situation where getting to an emergency room quickly matters.
Black Stool in Newborns
If you’re a new parent noticing very dark stool in a newborn, this is almost certainly normal. A baby’s first stool, called meconium, is blackish green, thick, and sticky. It’s made up of water, cells, mucus, hair, and other materials the baby swallowed in the womb. Most babies pass meconium within 24 to 48 hours after birth. After those first few days, stool color should gradually shift to yellow, green, or brown as the baby starts digesting milk. If black stool returns later in infancy after meconium has already cleared, that’s worth mentioning to your pediatrician.
What to Do Next
Start by thinking about what you’ve eaten or taken in the last day or two. If you’re on iron supplements, taking bismuth-based stomach medicine, or recently ate a large serving of blueberries or black licorice, give it a couple of days after stopping and see if the color returns to normal. That’s usually all it takes to confirm a harmless cause.
If you can’t connect the color to any food or supplement, or if the stool is sticky and tar-like with an unusually bad smell, contact your doctor. They can test a stool sample for hidden blood, which is a quick and straightforward way to determine whether bleeding is actually present. This test removes the guesswork and gives you a clear answer about whether further investigation is needed.