Green poop is usually a sign of something harmless: eating a lot of leafy greens, taking iron supplements, or food moving through your intestines faster than usual. In most cases, it resolves on its own within a day or two. Less commonly, green stool can signal a bacterial or viral infection, especially when paired with diarrhea.
Why Stool Is Normally Brown
Your liver produces bile, a yellow-green fluid that helps digest fats. When bile enters your intestines, bacteria break it down into a pigment called stercobilin, which gives stool its characteristic brown color. This conversion takes time. If food moves through your gut faster than normal, bile doesn’t fully break down, and your stool keeps that original green tint. This is the single most common reason for green poop that isn’t diet-related: rapid transit through the intestines, often from mild diarrhea or a stomach bug.
Foods That Turn Stool Green
Chlorophyll, the pigment that makes plants green, passes through your digestive system with its color largely intact. Spinach, kale, and broccoli are the most common culprits, but avocados, fresh herbs, matcha, and even pistachios contain enough chlorophyll to shift stool color noticeably. Blueberries can also produce green-tinged stool in some people.
Artificial food coloring is another frequent cause. Brightly frosted cupcakes, flavored drink mixes, ice pops, and candy with green or blue dyes continue tinting material as it moves through your gut. If your stool turns green a day after a birthday party or a round of colorful snacks, that’s almost certainly why.
Supplements and Medications
Iron supplements commonly turn stool dark green or even black. This is a well-known side effect and not a reason for concern on its own. Some antibiotics can also tint stool green or yellow, partly by disrupting the gut bacteria responsible for converting bile to its usual brown pigment. If the color change lines up with starting a new medication or supplement, that’s likely the explanation.
Infections That Cause Green Stool
Bacterial infections like Salmonella and E. coli can produce green diarrhea. These infections speed up intestinal transit dramatically, preventing bile from completing its color change. Viral infections, particularly norovirus (commonly called stomach flu), do the same thing. In these cases, green stool is almost always accompanied by other symptoms: watery diarrhea, cramping, nausea, or fever. The green color itself isn’t the problem. It’s a side effect of the rapid transit caused by the infection.
If green diarrhea lasts more than a couple of days, or if you notice signs of dehydration like dark urine, dizziness, or dry mouth, that warrants medical attention. The same applies if you develop a fever or see blood in your stool.
Green Stool in Babies
Green poop in infants has its own set of causes, most of them normal. Newborns pass meconium in their first few days, a dark greenish-black stool that’s completely expected. As feeding establishes, stool color shifts, but green tones can persist for several reasons.
Breastfed babies sometimes produce green stool if they don’t finish nursing on one side before switching. The earlier milk (foremilk) is lower in fat than the later milk (hindmilk), and missing that higher-fat portion can affect how the milk is digested, producing greener results. Babies on protein hydrolysate formula, which is designed for infants with milk or soy allergies, also tend to have green stool. Breastfed infants who haven’t yet developed a full population of gut bacteria may show green stool simply because those bacteria aren’t present in large enough numbers to convert bile pigments to brown.
Diarrhea in babies can also cause green stool for the same transit-time reason it does in adults. If your baby has persistent green diarrhea, seems unusually fussy, or shows signs of dehydration like fewer wet diapers, that’s worth a call to the pediatrician.
How Long Green Stool Typically Lasts
Diet-related green stool usually clears up within one to two bowel movements after you stop eating the trigger food. Medication or supplement-related changes persist as long as you’re taking the product. Infection-related green diarrhea generally resolves as the illness runs its course, typically within a few days to a week. If green stool continues for more than a few days without an obvious dietary explanation, or if it comes with fever, blood, or dehydration, it’s reasonable to get it checked out.