Black poop can range from dark greenish-black to jet black, depending on the cause. The most important visual clue isn’t just the color but the texture, consistency, and smell. A stool that’s black because of something you ate or a supplement you took looks and behaves very differently from one that’s black because of internal bleeding.
Two Types of Black Stool
Not all black poop is the same, and telling the two types apart matters. The first type is stool that’s been stained dark by something harmless you consumed. Iron supplements, bismuth-based medications like Pepto-Bismol, activated charcoal, black licorice, blueberries, and blood sausage can all turn stool black or very dark green. This kind of black stool typically holds its normal shape and texture. It may look unusually dark in the toilet, but it flushes normally and doesn’t have an unusual smell beyond what you’d expect.
The second type is called melena, and it looks distinctly different. Classic melena is jet black with a tarry, sticky consistency. Think of road tar or thick motor oil. It often sticks to the toilet bowl and can be difficult to flush. If you wiped and looked at the tissue, it would smear rather than come off cleanly. Melena also has a particularly strong, foul odor that’s noticeably worse than a typical bowel movement. That smell comes from blood being broken down as it passes through the digestive tract.
Why Bleeding Turns Stool Black
When bleeding happens high in the digestive tract, in the stomach or the first part of the small intestine, the blood doesn’t stay red. As it moves downward, digestive enzymes break down hemoglobin, the protein in red blood cells that carries oxygen. This chemical breakdown transforms the bright red color into a dark, almost black pigment by the time the blood reaches the end of the digestive tract. The process also produces that distinctive tarry stickiness and strong odor. The further the blood has to travel, the darker and more digested it becomes.
This is why bleeding lower in the digestive tract, closer to the rectum, typically produces bright red or maroon-colored blood instead. Red blood in or on your stool (called hematochezia) usually signals a problem in the colon or rectum, while black tarry stool points to something higher up.
How to Tell the Difference at Home
The single most reliable way to distinguish harmless black stool from melena is the smell. Stool darkened by iron pills, bismuth, or food won’t have an unusual or especially offensive odor. Melena has a smell that’s hard to ignore, often described as sickeningly sweet or rotten, and distinctly different from normal stool.
Texture is your second clue. If your stool is dark but formed, solid, and roughly the shape you’d expect, it’s more likely stained by something you consumed. Melena tends to be loose, sticky, and tar-like. It clings to surfaces and has an almost greasy quality.
Context helps too. Think back over the past day or two. Did you take an iron supplement, chew Pepto-Bismol tablets, eat a bowl of blueberries, or take activated charcoal? If so, you likely have your explanation. If nothing in your recent diet or medication use accounts for the color change, and especially if the stool is tarry and foul-smelling, that warrants prompt medical attention.
When Black Stool Signals a Problem
Melena on its own is a sign of bleeding in the upper digestive tract, which can come from ulcers, inflammation of the stomach lining, or other conditions. The amount of blood needed to produce melena is relatively small, so stool can appear very dark even from minor bleeding. But any amount of internal bleeding needs evaluation.
Pay attention to how you feel alongside the black stool. Dizziness or lightheadedness, feeling unusually weak or fatigued, a racing heartbeat, or abdominal pain alongside tarry black stool are all signs that bleeding may be significant. Vomiting material that looks like coffee grounds is another red flag, since that’s what partially digested blood looks like when it comes back up rather than passing through.
Testing for Hidden Blood
If there’s any doubt about whether black stool contains blood, your doctor can run a fecal occult blood test. This is a simple lab test performed on a small stool sample. The fecal immunochemical test is the more sensitive and commonly preferred version. It detects tiny amounts of blood that aren’t visible to the naked eye. A positive result confirms bleeding and typically leads to further investigation, such as an endoscopy, to find the source.
Black Stool in Newborns
If you’re a new parent, black poop in the first couple of days is completely normal. A newborn’s first stool, called meconium, is blackish-green, thick, and sticky, resembling tar or sludge. Unlike melena, meconium doesn’t smell. Your baby should pass meconium within 24 to 48 hours after birth, and the stool will gradually transition to a lighter color, typically yellowish or greenish, over the following days as feeding gets established. Black stool that appears after this initial transition period, or that returns later in infancy, is not normal and should be evaluated.