Healthy stool is some shade of brown, ranging from light tan to dark brown. That color comes from a bile pigment called stercobilin, a byproduct of your liver processing old red blood cells. Bile starts out green, and as it travels through your digestive tract, enzymes chemically break it down, gradually shifting the color from green to brown. When something interrupts that process, or when foods, supplements, or bleeding add their own pigments, your stool changes color.
Green Stool
Green is one of the most common color changes, and it’s usually harmless. Bile is naturally green when your liver first releases it. If food moves through your large intestine faster than normal, like during a bout of diarrhea, bile doesn’t have time to fully break down, and your stool stays green. Eating large amounts of leafy greens, drinking brightly colored beverages with green food dye, or taking iron supplements can also turn things green.
On its own, green stool that happens once or twice and lines up with something you ate is rarely a concern. If it persists for more than a few days with no obvious dietary explanation, it may point to an ongoing digestive issue worth investigating.
Yellow, Greasy, or Foul-Smelling Stool
Yellow stool that looks greasy, floats, and smells worse than usual often signals excess fat that your body failed to absorb. Normally, enzymes from your pancreas break down dietary fat so your intestines can absorb it. When that process falls short, undigested fat passes through and changes both the color and texture of your stool.
Several conditions can cause this. Celiac disease damages the lining of the small intestine so it can’t absorb nutrients properly. Chronic pancreatitis and cystic fibrosis can reduce the supply of digestive enzymes your pancreas produces. Crohn’s disease, small intestinal bacterial overgrowth (SIBO), and a parasitic infection called giardiasis can all interfere with fat absorption as well. An occasional pale-yellow stool after a high-fat meal is not unusual, but consistently greasy, floating stools are worth bringing up with your doctor.
Pale, Clay-Colored, or White Stool
Stool that looks pale gray, clay-colored, or almost white is a more urgent signal. The brown pigment in stool comes directly from bile, so when stool loses that color entirely, it typically means bile isn’t reaching your intestines. The most common reason is a problem with your biliary system: the network of your liver, gallbladder, and bile ducts.
Gallstones can physically block a bile duct. Hepatitis, cirrhosis, and fatty liver disease can reduce bile production. Tumors or cysts on the liver, bile ducts, pancreas, or gallbladder can also obstruct bile flow. Narrowing of the bile ducts (called biliary strictures) and inflammation of those ducts are less common but possible causes. In newborns, a condition called biliary atresia, where bile ducts don’t form correctly, can cause persistently pale stool and requires early treatment. Clay-colored stool that lasts more than a day or two, especially alongside dark urine, yellowing skin, or abdominal pain, warrants prompt medical attention.
Red or Maroon Stool
Red stool gets people’s attention, and for good reason, but it doesn’t always mean something is wrong. Beets, tomatoes, red peppers, and foods with red dye can all give stool a reddish tint. If you ate something red in the last day or two, that’s the likely culprit.
Bright red blood, on the other hand, usually points to bleeding from the lower digestive tract: the rectum or anus. The most common cause in middle-aged and older adults is hemorrhoids, which are swollen blood vessels around or just inside the anus. Anal fissures, small tears in the skin of the anal canal, also produce bright red blood that shows up on toilet paper or the surface of the stool. Certain intestinal infections from bacteria or parasites can cause bloody diarrhea with cramping as well.
Maroon-colored stool suggests the bleeding source is a bit higher up in the intestines, giving the blood more time to darken before it exits. If you see red or maroon stool that doesn’t match up with a food you recently ate, especially if it happens more than once or comes with pain, dizziness, or weakness, that combination needs medical evaluation quickly.
Black or Tarry Stool
Black stool has two very different explanations, and telling them apart matters. The harmless version comes from iron supplements, activated charcoal, or bismuth-based medications like Pepto-Bismol. These darken stool but don’t change its texture or smell in a distinctive way.
The concerning version is called melena: stool that’s jet black, tarry, sticky, and has a particularly strong, offensive odor. That smell comes from blood being digested as it travels through the GI tract. Melena usually indicates bleeding from the upper digestive system, such as a stomach ulcer or inflamed esophagus. The longer blood spends in your system before exiting, the darker and more foul-smelling it becomes. If your stool is black but you’re taking iron or bismuth, that’s likely the cause. If it’s black, sticky, and unusually foul without those supplements, treat it as urgent. A doctor can run a simple stool test to confirm whether blood is present.
Stool Color in Babies
Newborn stool follows a predictable color progression that can catch new parents off guard. Almost all babies pass meconium as their first bowel movements: thick, black, tarry-looking stool that built up in the intestines before birth. This is completely normal and clears within the first few days.
Once a baby starts breastfeeding or drinking formula, stool transitions to green or yellow with a more liquid consistency. Breastfed babies typically stay in the green-yellow-brown range for as long as they nurse. Formula-fed babies produce similar colors, sometimes slightly lighter. The key color to watch for in infants is white or very pale stool, which can indicate a bile duct problem and should be evaluated right away.
When Color Changes Are Worth Investigating
A single unusual stool that traces back to something you ate or a supplement you’re taking is almost never a problem. The color should return to brown within a day or two once that food or substance clears your system. Where it gets more serious is when a color change persists beyond a few days, recurs without an obvious dietary explanation, or shows up alongside other symptoms like fever, abdominal pain, diarrhea, unexplained weight loss, or dizziness.
Red and black stool tend to raise the most alarm because they can indicate bleeding. But persistent pale or clay-colored stool is equally important to address, since it can signal liver or gallbladder problems that worsen without treatment. If a doctor suspects hidden blood in your stool, they may order a fecal occult blood test, which detects blood that isn’t visible to the naked eye. A positive result doesn’t identify the source of bleeding on its own, so it’s typically followed by a colonoscopy to get a direct look inside the colon.
Paying attention to what you ate in the last 24 to 48 hours is the simplest first step. If diet explains the change and the color normalizes, you can move on. If it doesn’t, the color itself is a useful clue that helps your doctor narrow down what’s happening and where.