Green poop is almost always harmless. The most common cause is simply eating a lot of green vegetables or foods with green dye, though faster-than-normal digestion can also turn your stool green by interrupting the chemical process that normally makes it brown.
Why Stool Is Normally Brown
Your liver produces bile, which starts out greenish-yellow. As bile travels through your intestines, bacteria in your colon break it down into compounds called urobilinoids. These are initially colorless but oxidize into an orange-brown pigment, which is what gives stool its typical color. The whole journey from mouth to toilet takes anywhere from 10 to 73 hours in healthy adults, with most of that time spent in the colon where this color transformation happens.
When anything disrupts that process, whether by speeding food through the gut or overwhelming the system with green pigments, stool can come out green instead of brown.
Foods That Turn Stool Green
Chlorophyll is the most common culprit. It’s the pigment that makes plants green, and it can do the same to your poop. Eating generous amounts of spinach, kale, or broccoli is the classic cause, but other chlorophyll-rich foods can have the same effect: avocados, fresh herbs, matcha, and even pistachios (which get their green color from chlorophyll and related plant pigments). Blueberries, surprisingly, can also produce green stool.
Artificial food dyes are another frequent cause. Brightly colored frosting, candy, or sports drinks can tint stool in unexpected ways. If you eat enough rainbow-colored candy, the mixed dyes can even make stool look black. The effect typically shows up within a day or two and clears once you stop eating the food in question.
Fast Digestion and Green Bile
If food moves through your intestines faster than usual, bile doesn’t have enough time to be fully broken down by gut bacteria. The result is stool that still carries bile’s original green color. This is why diarrhea often looks green regardless of what you ate. Anything that speeds up transit, including a stomach bug, food intolerance, stress, or even a strong cup of coffee on an empty stomach, can produce this effect.
Colonic transit alone normally takes 10 to 59 hours. When that window shrinks significantly, the brown-making bacteria simply don’t have time to finish the job.
Medications and Supplements
Iron supplements are a well-known cause of darker or greenish stool. Antibiotics can also cause green poop by killing off some of the gut bacteria responsible for converting bile pigments to brown. If you recently started a new antibiotic course and notice the change, that connection is likely the explanation. The color typically returns to normal after you finish the medication and your gut bacteria repopulate.
Green Stool in Babies
Green poop is especially common in infants and usually not a concern. In breastfed babies, it can happen when a baby doesn’t fully finish feeding on one side, missing some of the higher-fat milk that comes later in a feeding. That fat content affects how breast milk is digested, and without it, stool can turn green. Breastfed newborns may also have green stool simply because their gut bacteria haven’t fully established yet.
Formula-fed babies on specialized hydrolyzed formulas (used for milk or soy allergies) commonly produce green stool as well. And just like adults, babies with diarrhea may have green poop because of faster transit time.
When Green Stool Needs Attention
A single green bowel movement, or even a few days of green stool after a big salad or a course of antibiotics, is not something to worry about. The Mayo Clinic recommends contacting a healthcare professional if green stool persists for more than a few days without an obvious dietary explanation. Seek immediate medical attention if green stool is accompanied by signs of dehydration, particularly in young children. Dehydration signs include dry mouth, reduced urination, and in infants, fewer wet diapers than usual or no tears when crying.
Persistent green diarrhea alongside fever or severe abdominal pain could point to an infection that needs treatment. But in most cases, green poop is your digestive system reacting normally to something you ate or to a temporary change in how quickly food is moving through you.