Normal stool is brown because of a pigment called stercobilin, a dark orange compound produced when your gut bacteria break down bile. The shade can range from light tan to deep brown and still be perfectly healthy. Changes in color usually reflect something you ate or drank, but certain colors can signal a problem worth paying attention to.
Why Stool Is Brown in the First Place
The brown color of stool starts with the breakdown of old red blood cells. Your body recycles the iron-containing molecule in red blood cells (heme) by splitting it apart, eventually producing a yellow compound called bilirubin. Your liver makes bilirubin water-soluble by attaching sugar molecules to it, then sends it into your intestines through bile.
Once in the gut, bacteria go to work. A single enzyme called bilirubin reductase converts bilirubin into a colorless compound called urobilinogen. That compound then oxidizes and breaks down further into stercobilin, the pigment that gives stool its characteristic brown. Anything that disrupts this chain, whether it’s a change in bile flow, gut transit speed, or bacterial activity, can shift the color.
Green Stool
Green stool is common and almost always harmless. The two main causes are diet and speed. Leafy greens like spinach and kale contain chlorophyll that can tint your stool green, especially in large amounts. Green food coloring in drink mixes, ice pops, and candy does the same thing. Iron supplements are another frequent culprit.
The other explanation is rapid transit. Bile starts out green when it enters your intestines. As bacteria process it during the slow trip through your colon, it gradually turns brown. If food moves through too quickly, often because of diarrhea, bile doesn’t fully break down, and stool comes out green. If the green color goes away once your digestion normalizes or you change your diet, there’s nothing to worry about.
Yellow, Greasy Stool
Occasional yellow stool isn’t alarming, but stool that’s consistently yellow, greasy, foul-smelling, and tends to float points to fat malabsorption. This happens when your body can’t properly digest or absorb the fat in your food, so it ends up in your stool instead.
The most common reasons fall into two categories. The first is pancreatic insufficiency, where your pancreas doesn’t produce enough digestive enzymes. This can result from chronic pancreatitis, cystic fibrosis, or pancreatic cancer. The second is damage or disease in the small intestine itself. Celiac disease, Crohn’s disease, small intestinal bacterial overgrowth (SIBO), and parasitic infections like giardia can all interfere with fat absorption. If you’re noticing oily, pale-yellow stools that leave a greasy residue in the toilet bowl on a regular basis, that pattern is worth investigating.
Pale, Clay, or White Stool
Stool gets its brown color from bile salts released by the liver. When stool turns pale, clay-colored, or chalky white, it typically means bile isn’t reaching your intestines in normal amounts. This points to a problem somewhere in the biliary system: the network connecting your liver, gallbladder, and pancreas.
Gallstones are the most common culprit. A stone can block the bile duct and cut off the flow of bile entirely. Other causes include narrowing of the bile ducts, liver infections that reduce bile production, cysts in the bile ducts, and tumors of the liver, bile ducts, or pancreas. Pale stool that persists for more than a day or two is one of the color changes most likely to indicate a real medical issue, especially if it comes with dark urine, yellowing skin, or abdominal pain.
Black Stool
Black stool has two very different explanations: one harmless, one serious.
The harmless version comes from what you’ve consumed. Pepto-Bismol and other bismuth-containing medications commonly turn stool black. So do iron supplements, activated charcoal, black licorice, blueberries, and blood sausage. If you can trace the color to something you recently ate or took, that’s almost certainly the cause.
The serious version is called melena: black, tarry, sticky stool with a distinctive foul smell. This appearance comes from blood that has been digested as it travels through the GI tract, and it typically signals bleeding in the upper digestive system (the stomach, esophagus, or upper small intestine). Bleeding from the right side of the colon or the small bowel can also produce it. If your black stool is tarry and sticky rather than simply dark, and you haven’t taken any of the substances listed above, that’s a red flag.
Red or Bloody Stool
Bright red blood in or on stool usually comes from the lower digestive tract: the colon, rectum, or anus. Hemorrhoids and anal fissures are the most frequent causes, and both are common. Diverticular disease and inflammatory conditions like ulcerative colitis can also produce visible red blood.
Before assuming the worst, consider what you’ve eaten in the past 48 hours. Beets are notorious for turning stool (and urine) red or pink. Dragon fruit, blackberries, rhubarb, and foods with red dye can all mimic the appearance of blood. If you’ve eaten any of these recently, give it a couple of days and see if the color normalizes.
In rarer cases, bright red blood can actually come from vigorous bleeding in the upper GI tract that moves through the intestines rapidly. The key distinction is volume and context. A streak of red on toilet paper after straining is very different from a toilet bowl full of red or dark blood, which needs prompt evaluation.
Stool Color in Newborns
Infant stool follows a predictable color progression that can surprise new parents. A newborn’s first stools are meconium: a thick, sticky, greenish-black substance that looks like tar. This is completely normal and clears within the first couple of days.
After meconium passes, stool transitions to a greenish-brown, then settles into a color that depends on feeding. Breastfed babies typically produce loose, mustard-yellow stool, sometimes with small seed-like flecks. Formula-fed babies tend toward tan or yellowish-brown. In infants, pale or white stool is the color that warrants the most concern, as it can indicate a problem with bile flow that needs early detection.
What’s Worth Tracking
A one-time color change after a big serving of beets or a course of iron supplements is nothing to act on. What matters more is persistence and context. Stool that stays an unusual color for several days without a dietary explanation, or that comes with symptoms like abdominal pain, unexplained weight loss, fever, or dizziness, tells a different story. Black tarry stool, persistent pale or clay-colored stool, and significant amounts of red blood are the three color changes that most reliably point to something that needs medical attention.