Dark brown stool is usually normal. The color that crosses into concerning territory is jet black, especially when the stool is also tarry, sticky, and has an unusually strong smell. That combination suggests digested blood, not just a dark meal. A stool that’s simply dark brown, even very dark brown, is almost always harmless.
Normal Dark Stool vs. Concerning Black Stool
Stool color naturally ranges from light brown to very dark brown depending on what you’ve eaten, how hydrated you are, and how long food spent in your digestive tract. Slower transit time means more bile breakdown, which deepens the brown color. None of this is a problem.
The line you’re looking for isn’t just about darkness. It’s about a specific combination of features. Medically significant black stool, called melena, is jet black with a tarry, sticky consistency, almost like roofing tar. It also has a distinctly foul odor that’s noticeably worse than regular stool. That smell comes from blood being broken down by stomach acid and digestive enzymes as it moves through your gut. The longer the blood travels through your system, the darker and more pungent it becomes.
A small amount of internal bleeding can look more dark brown than black, so color alone isn’t always a reliable indicator. The sticky texture and strong odor are the more telling signs. If your stool is dark but has a normal consistency and doesn’t smell markedly different, it’s far less likely to involve blood.
What Makes Stool Black Without Bleeding
Several everyday foods and supplements turn stool very dark or even black, with no blood involved at all. The most common culprits:
- Iron supplements: One of the most frequent causes of harmless black stool. If you recently started taking iron, this is likely your answer.
- Bismuth subsalicylate: The active ingredient in Pepto-Bismol. It reacts with trace sulfur in your digestive tract and turns stool black, sometimes for several days after a single dose.
- Dark-colored foods: Blueberries, black licorice, beets, dark chocolate, and foods with dark food coloring can all darken stool significantly.
Stool that’s been stained by food or supplements won’t have the sticky, tarry texture or the distinctively awful smell of digested blood. That’s the practical way to tell the difference at home. If you can connect the timing to something you ate or a supplement you started, and the stool looks dark but otherwise normal, you’re probably fine.
Why Blood Turns Stool Black
When bleeding happens in the stomach or upper part of the small intestine, the blood doesn’t stay red. Stomach acid converts the hemoglobin in red blood cells into a dark brown-black compound. By the time this digested blood reaches the end of your digestive tract, it’s been chemically transformed enough to turn the entire stool black and give it that characteristic tar-like appearance.
The location of bleeding matters for what you’ll see. Bleeding in the stomach typically produces black, tarry stool. Bleeding higher in the colon or small intestine tends to produce dark red or maroon stool. Bleeding low in the colon, rectum, or anus usually shows up as bright red blood on the stool or on toilet paper. The farther blood has to travel through your digestive system, the darker it gets.
When Dark Stool Needs Attention
Black, tarry stool that you can’t explain with diet or supplements warrants a call to your doctor. It doesn’t always mean something serious, but upper GI bleeding can come from stomach ulcers, inflammation of the stomach lining, or other conditions that benefit from early treatment.
Certain symptoms alongside dark stool make the situation more urgent. Feeling lightheaded or dizzy, vomiting blood (which may look like coffee grounds rather than bright red), or feeling unusually weak or faint could indicate enough blood loss to affect your blood pressure. That’s a situation for same-day medical care, not a wait-and-see approach.
If your doctor wants to check whether dark stool actually contains blood, they’ll use a simple stool test. The most accurate version, called a fecal immunochemical test, detects hidden blood with about 86 to 92 percent sensitivity. It’s a straightforward at-home collection that gets sent to a lab, and it can pick up bleeding that isn’t visible to the naked eye.
Dark Stool in Newborns
If you’re asking about a baby, the rules are different. Newborns pass meconium, their first stool, within 24 to 48 hours of birth. Meconium is dark greenish-black, thick, and sticky. This is completely normal and expected. It’s made up of materials the baby ingested in the womb, not blood.
Over the first few days of life, stool gradually transitions from black-green to yellow-green to the mustard-yellow color typical of breastfed infants, or tan-brown for formula-fed babies. If a newborn hasn’t passed meconium within 48 hours, that could signal an intestinal blockage or another condition that needs evaluation. And if dark black stool reappears after the meconium phase has passed, that’s worth bringing up with your pediatrician, since it’s no longer expected at that point.