Green poop is almost always harmless. It usually means you ate something green, food moved through your intestines faster than normal, or you’re taking a supplement or medication that changes stool color. In most cases, your next bowel movement will look perfectly normal without you doing anything differently.
How Stool Gets Its Normal Brown Color
Your liver produces bile, a digestive fluid that starts out yellow-green. As bile travels through your intestines, bacteria living in your gut chemically convert its pigments into a brown compound called stercobilin. This is what gives stool its typical brown color. The process takes time, though. If anything disrupts it, whether that’s speed, diet, or changes to your gut bacteria, stool can stay green.
Foods That Turn Stool Green
The most common culprit is chlorophyll, the pigment that makes plants green. Eating generous amounts of spinach, kale, broccoli, avocados, herbs, or matcha can tint your stool bright green. Pistachios contain chlorophyll too and can have the same effect. Even blueberries, surprisingly, can produce greenish shades.
Artificial food coloring is another frequent cause. Brightly frosted cupcakes, flavored drink mixes, ice pops, and green-dyed candy keep their tinting power all the way through your digestive tract. If you ate something with vivid coloring in the last day or two, that’s likely your answer.
Fast Digestion and Diarrhea
When food moves through your intestines faster than usual, gut bacteria don’t have enough time to fully convert bile from green to brown. The result is greenish stool. This is why green poop often shows up alongside diarrhea, whether from a stomach bug, food intolerance, stress, or anything else that speeds up your digestion. Once your bowel movements return to a normal pace, the color typically follows.
Medications and Supplements
Several common over-the-counter products can change stool color:
- Iron supplements often darken stool to a deep green or even black-green. This is one of the most common supplement-related causes.
- Antibiotics can disrupt the balance of gut bacteria responsible for converting bile pigments, leading to green or yellowish stool.
- Bismuth subsalicylate (the active ingredient in some antidiarrheal medications) reacts with sulfur in your digestive system and can turn stool dark green or black.
- Antacids containing aluminum hydroxide can produce a greenish tint.
If you recently started any of these, that’s very likely the explanation. The color change is a cosmetic side effect, not a sign of harm.
Green Stool in Babies
Green poop in infants is common and has its own set of causes. Newborns pass meconium in their first days, which is dark green to black and completely normal. After that transition, breastfed babies may produce green stool if they don’t finish feeding on one side. This means they get more of the lower-fat milk at the start of a feeding and less of the higher-fat milk that comes later, which can affect how the milk is digested.
Babies on protein hydrolysate formula (used for milk or soy allergies) also tend to have greener stool. Breastfed infants sometimes lack the full range of intestinal bacteria needed to complete the bile conversion process, which can keep stool greenish for a while. Diarrhea in babies causes green stool for the same transit-time reason it does in adults.
When Green Stool Signals a Problem
A single green bowel movement, or even a few in a row after a big salad or a round of antibiotics, is not a concern. But green stool lasting more than a few days without an obvious dietary or medication explanation is worth mentioning to a doctor. The same goes if green stool comes with persistent diarrhea, since dehydration is the real risk there, especially in young children. Drink plenty of fluids and seek prompt care if you notice signs of dehydration like dizziness, dry mouth, or dark urine.
Green stool on its own is not a sign of cancer, internal bleeding, or serious organ disease. Black, tarry stool or red-streaked stool are the color changes that warrant more urgent attention. Green is, overwhelmingly, the least worrisome color change your stool can make.