Black diarrhea can be a sign of bleeding in your upper digestive tract, which is a serious medical situation. It can also be completely harmless, caused by something you ate or a supplement you took. The key difference comes down to texture, smell, and whether you have other symptoms alongside it.
Why Stool Turns Black
When bleeding occurs high up in the digestive tract, typically in the stomach or upper small intestine, the blood doesn’t stay red. Digestive chemicals interact with it as it travels downward, turning it black and giving it a thick, tar-like consistency. This type of black stool has a medical name: melena. It also has a distinctly foul smell that’s noticeably different from normal stool.
But blood isn’t the only thing that turns stool black. Several foods and supplements do the same thing without any danger at all. Black licorice, blueberries, blood sausage, iron supplements, activated charcoal, and bismuth-based medications like Pepto-Bismol can all produce dark or black stool. In these cases, the color change is temporary and stops once the substance clears your system.
How to Tell the Difference
The most important clue is texture. Melena from internal bleeding is sticky, tar-like, and coats the toilet bowl. It has an unusually strong, unpleasant odor. Black stool from food or supplements, on the other hand, tends to look more like normal stool that just happens to be darker. It won’t have that sticky, tarry quality.
Think about what you’ve consumed in the last day or two. If you recently took Pepto-Bismol, started an iron supplement, or ate a large serving of blueberries, that’s likely your explanation. If nothing in your diet or medication routine explains the color, the cause is more concerning.
Medical Causes of Black Stool
When black, tarry diarrhea does signal bleeding, the source is usually in the stomach or upper small intestine. The most common conditions behind it include:
- Peptic ulcers: open sores in the stomach lining or the first part of the small intestine, often linked to certain bacteria or long-term use of anti-inflammatory painkillers
- Severe inflammation: irritation of the stomach lining (gastritis) or the esophagus (esophagitis)
- Erosion of the stomach lining: sometimes caused by alcohol, medications, or critical illness
- Ruptured veins in the esophagus or stomach: swollen blood vessels that can burst, often associated with liver disease
- Esophageal tears: caused by forceful or prolonged vomiting
- Cancer: tumors in the stomach, esophagus, or pancreas can cause slow or sudden bleeding
Peptic ulcers are by far the most frequent culprit. If you’ve been dealing with stomach pain, heartburn, or nausea alongside the black stool, an ulcer is a strong possibility.
Warning Signs That Need Immediate Attention
Black, tarry diarrhea on its own warrants a call to your doctor. But certain accompanying symptoms suggest the bleeding is significant and needs urgent care. Dizziness or lightheadedness, a rapid heartbeat, feeling faint, vomiting (especially if the vomit looks like coffee grounds), cold or clammy skin, and unusual weakness or fatigue all point to enough blood loss that your body is struggling to compensate. If you experience any of these alongside black stool, treat it as an emergency.
Black Stool in Babies
Newborns pass a greenish-black, tar-like stool called meconium during their first few days of life. This is completely normal. It’s the result of everything the baby swallowed in the womb: amniotic fluid, mucus, bile, and other materials. After the first three days, though, black tarry stool in a baby is no longer expected. In an infant older than three days, black stool may indicate that blood has entered the baby’s digestive tract, and it needs medical evaluation promptly.
What You Should Do
Start by ruling out the simple explanations. If you can trace the color to a food, supplement, or medication, stop taking it for a day or two and see if the stool returns to normal. Iron supplements are one of the most common culprits people overlook.
If you can’t identify an obvious dietary cause, or if the stool is sticky and tar-like with an unusually strong odor, that pattern points toward bleeding in the upper digestive tract. This is especially true if you also feel weak, dizzy, nauseous, or have stomach pain. The combination of black, tarry diarrhea with any of those symptoms is not something to wait out or monitor at home.