Black poop is usually harmless and caused by something you ate, drank, or took as a supplement. But in some cases, it signals bleeding in the digestive tract. The key distinction comes down to texture and smell: harmless black stool looks normal aside from its color, while stool darkened by blood is sticky, tarry, and has a noticeably foul odor.
Common Foods and Supplements That Turn Stool Black
Blueberries are one of the most common culprits. Eating a large amount can tint stool so dark it looks almost black. Black licorice does the same thing, as can heavily dyed candies, where multiple food colorings mix together in the gut and produce a dark result. Dark leafy greens, beets, and foods with dark food coloring can also shift stool color noticeably.
Iron supplements are a frequent cause. They often turn stool dark green or outright black, and this is completely expected. If you recently started an iron supplement and noticed the change, that’s almost certainly the explanation.
Pepto-Bismol and similar bismuth-based stomach medications are another well-known cause. The active ingredient, bismuth, reacts with trace amounts of sulfur in your saliva and digestive system to form a black compound. This can make your stool jet black. The effect usually fades within several days of stopping the medication.
How to Tell If It’s Blood
Black stool caused by bleeding in the digestive tract has a medical name: melena. It looks and feels distinctly different from stool that’s just been darkened by food or supplements. Classic melena is jet black with a tarry, sticky consistency, almost like roof tar. It also has a uniquely strong, offensive smell that’s hard to miss. That odor comes from blood being broken down as it travels through the digestive tract. The longer blood has been in the gut, the darker and more pungent the stool becomes.
If your black stool has a normal texture and doesn’t smell unusually foul, it’s very likely dietary. If it’s sticky, shiny, and has a smell that strikes you as distinctly worse than usual, that’s a different situation.
What Causes Bleeding in the Digestive Tract
Melena typically comes from bleeding in the upper digestive tract, meaning the esophagus, stomach, or the first part of the small intestine. By contrast, bleeding lower in the digestive system (the colon or rectum) usually shows up as bright red blood in or on the stool. The reason upper bleeding produces black stool is that stomach acid and digestive enzymes break down the blood over hours as it moves through the system.
Common causes of upper digestive bleeding include stomach ulcers, inflammation of the stomach lining, and tears in the esophagus. One significant and often overlooked risk factor is regular use of common painkillers like ibuprofen, naproxen, and aspirin. These nonsteroidal anti-inflammatory drugs (NSAIDs) can damage the stomach lining and increase the risk of upper digestive bleeding up to fourfold. Among the most commonly used options, ibuprofen carries the lowest risk, roughly doubling it, while naproxen increases the risk about fourfold. Taking these medications alongside certain antidepressants (SSRIs) compounds the risk further.
Alcohol use, especially heavy drinking, can also contribute by irritating the stomach lining or worsening existing ulcers.
Black Stool in Newborns
If you’re a new parent, black stool in a newborn is completely normal. A baby’s first bowel movements consist of meconium, a thick, dark, tar-like substance that accumulated in the intestines before birth. Babies typically pass meconium within 24 to 48 hours after delivery, and the stool gradually transitions to lighter colors over the following days as feeding begins.
If a newborn hasn’t passed meconium within 48 hours, that can indicate a medical issue such as an intestinal blockage or other conditions that need evaluation.
When Black Stool Needs Attention
A single episode of black stool after eating blueberries or taking Pepto-Bismol doesn’t require any action. But certain combinations of symptoms point to something more serious. Lightheadedness, dizziness, or feeling faint alongside black stool suggests enough blood loss to affect your blood pressure. Pale skin, unusual fatigue, or a racing heartbeat are also signs that bleeding may be significant.
If you can’t connect the color change to a food, supplement, or medication you’ve recently taken, it’s worth paying attention. And if the stool has that characteristic tarry, sticky quality with a strong odor, that’s the clearest signal to get evaluated promptly. Severe bleeding can require hospitalization, but many causes of upper digestive bleeding are treatable once identified.
How Doctors Check for Hidden Blood
When stool color is ambiguous, a simple stool test can detect blood that isn’t visible to the naked eye. The newer version of this test, called FIT, is more accurate than the older method for detecting blood. It specifically targets human blood proteins, which reduces false positives from dietary factors. The test is noninvasive and can be done at home with a kit from your doctor’s office. If the test is positive, further evaluation with an endoscopy or colonoscopy typically follows to locate the source of bleeding.