Black stool usually means one of two things: something you ate or swallowed temporarily changed the color, or there’s bleeding somewhere in your upper digestive tract. The difference between a harmless cause and a serious one comes down to texture, smell, and how you feel overall. Most of the time, the explanation is something simple, but knowing what to look for helps you figure out when it matters.
Harmless Causes That Turn Stool Black
Several everyday foods, supplements, and medications can darken your stool enough to make it look black or very dark green. The most common culprits are iron supplements, Pepto-Bismol (and other bismuth-containing products), activated charcoal, black licorice, blueberries, and blood sausage. When these are the cause, your stool may look darker than usual, but it keeps a relatively normal texture and doesn’t have an unusually foul smell. The color change stops within a day or two after you stop eating the food or taking the supplement.
If you recently started iron pills or took Pepto-Bismol for an upset stomach, that’s almost certainly your answer. There’s nothing to worry about, and no action needed.
When Black Stool Signals Bleeding
The medical term for black stool caused by bleeding is melena, and it looks and smells distinctly different from stool that’s been darkened by food. Melena is jet black with a tarry, sticky consistency, almost like asphalt or roofing tar. It also has a strong, offensive odor that’s noticeably worse than normal. That smell comes from blood being broken down and digested as it moves through your system.
The blackness happens because blood from the upper digestive tract (stomach, esophagus, or the first part of the small intestine) gets partially digested before it reaches the colon. By the time it comes out, the iron in the blood has oxidized, turning it dark black rather than red. Bleeding lower in the digestive tract, by contrast, tends to produce red or maroon-colored stool because the blood doesn’t have time to be broken down.
Upper digestive bleeding is roughly four times more common than lower digestive bleeding. It’s twice as common in men as in women, and the risk increases significantly after age 60.
Common Causes of Upper Digestive Bleeding
Stomach ulcers are the most frequent source. These are open sores on the lining of your stomach or the upper part of your small intestine, often caused by a bacterial infection or long-term use of anti-inflammatory painkillers like ibuprofen or aspirin. Inflammation of the stomach lining (gastritis) can also produce enough bleeding to cause melena, as can tears in the esophagus from forceful vomiting.
Less common but more serious causes include esophageal varices (swollen veins in the esophagus, typically related to liver disease) and tumors in the stomach or upper intestine. The severity ranges widely. Some people have slow, minor bleeding that only shows up in their stool color, while others experience acute episodes that require emergency care.
How to Tell the Difference
Three features separate melena from food-stained stool:
- Texture: Melena is tarry and sticky. Diet-related black stool has a normal consistency.
- Smell: Melena has a distinctly strong, foul odor you won’t get from iron pills or blueberries.
- Duration: If you can’t connect the color to a specific food, supplement, or medication, and it persists for more than a couple of bowel movements, bleeding is more likely.
Think about what you’ve eaten or taken in the last 24 to 48 hours. If nothing on the harmless list applies, the tarry texture and smell become much more important clues.
Warning Signs That Need Immediate Attention
Black, tarry stool on its own warrants a call to your doctor. But certain additional symptoms suggest severe or acute bleeding that needs emergency care. These include vomiting blood or material that looks like coffee grounds, feeling lightheaded or faint, a racing heart, cold or clammy hands and feet, pale skin, confusion, or excessive sweating. These are signs of shock from significant blood loss, which is life-threatening.
Overall mortality from upper digestive bleeding runs between 6% and 10%, which is why it’s taken seriously in medical settings. The risk of complications is higher if you’re over 60, have cardiovascular disease, or have a blood-clotting disorder.
How Doctors Investigate It
If your doctor suspects bleeding, the first step is usually a stool test that checks for hidden blood you can’t see with the naked eye. This is called a fecal occult blood test, and it simply involves providing a small stool sample. There are two versions: one uses a chemical reaction to detect blood, and the other uses antibodies that attach to a protein in blood cells. Both are quick and noninvasive.
If hidden blood is confirmed, the next step is typically a colonoscopy or an upper endoscopy, where a thin tube with a camera is guided through your digestive tract to locate the source. In some cases, a CT scan with contrast dye can provide detailed images of the entire colon and rectum. These procedures pinpoint where the bleeding is coming from, which determines the treatment approach.
Black Stool in Newborns and Infants
If you’re a parent noticing black stool in a baby, the context matters a lot. In the first few days of life, black, tar-like stool is completely normal. This is called meconium, and it’s made up of everything the baby swallowed in the womb: amniotic fluid, mucus, bile, and other materials. It’s thick, sticky, and dark greenish-black.
After the first three days, though, meconium should be gone. If a baby older than three days passes black, tarry stool, it could be a sign that blood has entered their digestive tract, and it needs medical evaluation. The same applies if you ever notice blood, mucus, or white and clay-colored stool in an infant of any age.