Stool color is primarily determined by bile, a digestive fluid your liver produces, and the foods you eat. Healthy stool ranges from light to dark brown, though temporary shifts into green, yellow, or even red are often harmless. Understanding what each color signals can help you tell the difference between a dietary quirk and something worth investigating.
Why Normal Stool Is Brown
The brown color of stool comes from a pigment called stercobilin, and the process that creates it starts with your red blood cells. As old red blood cells break down, they release a compound called heme. Your body converts heme first into a green pigment (biliverdin), then into a yellow one (bilirubin). Your liver makes bilirubin water-soluble and sends it into your small intestine through bile.
Once bilirubin reaches your gut, bacteria go to work on it. A specific bacterial enzyme reduces bilirubin into a colorless compound called urobilinogen, which then gets oxidized and further broken down into stercobilin, a dark orange-brown pigment. That final product is what gives stool its characteristic color. The whole chain depends on bile flowing freely from your liver, enzymes working properly, and gut bacteria doing their job. When any link in that chain is disrupted, stool color changes.
Green Stool
Green stool has two common explanations: diet and speed. Bile starts out yellow-green and only turns brown after enzymes in your intestines have time to chemically alter it. If food moves through your large intestine too quickly, as happens with diarrhea, bile doesn’t fully break down and stool stays green. This is probably the most common non-dietary cause of green stool, and it resolves once your digestion returns to normal.
On the dietary side, large servings of leafy greens like spinach or kale, green food coloring in drink mixes or ice pops, and iron supplements can all turn stool dark green. Iron supplements sometimes produce a shade so dark it looks almost black, which can be alarming but is harmless.
Yellow or Greasy Stool
Occasional yellow stool isn’t unusual, but stool that’s consistently yellow, oily, foul-smelling, or that floats is a sign of fat malabsorption. This means your digestive system is struggling to break down and absorb dietary fat, so it passes through and comes out in your stool. The texture is often loose or mushy, and you may notice an oily film on the toilet water.
Fat malabsorption can stem from problems in several organs. Your pancreas may not be producing enough digestive enzymes. Your liver or gallbladder may not be delivering enough bile. Conditions like celiac disease can damage the lining of your small intestine and impair absorption. Infections, including the parasite Giardia, can also trigger it. If yellow, greasy stools persist for more than a few days, the underlying cause usually needs to be identified.
Pale, Clay, or White Stool
Pale or clay-colored stool is one of the more medically significant color changes because it points to a lack of bile reaching your intestines. Without bile, stool loses its pigment entirely and appears light beige or chalky white. The technical term for this is acholic stool.
In adults, the most common causes are blockages in the bile ducts, such as gallstones, tumors, or inflammation that physically prevents bile from draining into the small intestine. Liver diseases that reduce bile production can have the same effect. In newborns, a condition called biliary atresia, where the bile ducts are blocked or absent from birth, produces persistently pale stools. Babies older than two weeks who have pale poop along with jaundice (yellowing of the skin) need prompt evaluation. Bismuth-based medications like Pepto-Bismol can sometimes lighten stool as well, but truly clay-colored stool that persists warrants medical attention.
Black Stool
Black stool falls into two very different categories, and the distinction matters. The harmless kind comes from something you consumed: iron supplements, Pepto-Bismol, or dark foods like black licorice or blueberries. This type of black stool has a normal texture and no unusual smell.
The concerning kind is called melena: jet-black stool that’s tarry, sticky, and has a distinctly strong, offensive odor. The smell is a byproduct of blood being digested as it moves through your gastrointestinal tract. Melena typically signals bleeding in the upper digestive system, such as from a stomach ulcer, an inflamed esophagus, or another source above the small intestine. The blood turns black because stomach acid and enzymes break it down during digestion. If your stool is black and sticky rather than just dark, and you haven’t taken iron or bismuth medications, that’s a situation that needs medical evaluation quickly.
Red Stool
Red stool can look alarming, but the cause ranges from completely benign to genuinely urgent. On the harmless end, beets are the classic culprit. The pigments in beets (called betalains) can turn both stool and urine pink or red, and the effect typically clears within 48 hours. Tomato products, cranberries, and red food coloring can do the same. If you’ve eaten one of these foods and the color disappears within two days, there’s nothing to worry about.
Bright red blood in stool, on the other hand, usually indicates bleeding in the lower part of your digestive tract: the colon, rectum, or anus. Hemorrhoids are the most common cause. They’re swollen veins in the rectum or anus, often triggered by straining during constipation, and they tend to produce small amounts of bright red blood on the toilet paper or surface of the stool. Anal fissures, which are small tears in the lining of the anal canal, cause similar bleeding along with sharp pain. Diverticulitis, where small pouches in the colon wall become infected and inflamed, can also cause bleeding when the fragile blood vessels inside those pouches rupture.
The volume and pattern of bleeding help distinguish minor from serious causes. A few drops on the toilet paper after a hard bowel movement is very different from large amounts of blood mixed into the stool, which could signal a more significant problem in the colon.
What’s Normal for Babies
Infant stool follows its own color timeline, and new parents often find it surprising. A newborn’s first several bowel movements consist of meconium, a thick, black, tarry substance that built up in the intestines before birth. This is completely normal and doesn’t signal bleeding.
Once meconium passes (usually within the first few days), stool transitions to shades of yellow, brown, and green, all of which are considered healthy. Breastfed babies typically produce mustardy yellow stool with a seedy texture. Formula-fed babies tend toward yellow-tan with hints of green. The key color to watch for in infants is persistent pale or white stool, especially when paired with jaundice, as this can indicate biliary atresia or another bile duct problem.
Medications and Supplements That Change Color
Several common medications can alter stool color in ways that mimic more worrisome conditions. Iron supplements frequently turn stool dark green or black. Bismuth subsalicylate (the active ingredient in Pepto-Bismol) can produce jet-black stool that looks similar to melena but lacks the tarry texture and foul odor. Some antibiotics shift stool to yellow or green by disrupting the gut bacteria responsible for converting bile pigments to their usual brown.
If you’ve recently started a new medication and notice a stool color change, check the side effect information. In most cases, the color returns to normal once you stop taking the medication.
How Long Diet-Related Changes Last
Most food-related stool color changes resolve within one to two days, since that’s roughly how long it takes for food to pass completely through your digestive tract. Beets, for example, typically clear within 48 hours. If a color change persists beyond that window and you can’t link it to something you’re eating regularly, it’s more likely to reflect something happening inside your digestive system rather than on your plate.