Green poop is almost always normal and not a sign of anything serious. The most common causes are everyday things: eating leafy greens, consuming foods with blue or purple dyes, or taking iron supplements. In most cases, the color returns to its usual brown within a day or two once the trigger passes through your system.
To understand why stool sometimes turns green, it helps to know why it’s normally brown in the first place, and what can interrupt that process.
Why Stool Is Usually Brown
Your liver produces bile, a yellow-green fluid that helps digest fats. When bile first enters your intestines, it’s actually green, thanks to a pigment called biliverdin. As waste moves through the colon, bacteria break that pigment down through several chemical steps, eventually producing a dark orange-brown compound called stercobilin. That’s what gives stool its characteristic color.
This breakdown process takes time. In a healthy adult, waste spends roughly 30 to 40 hours traveling through the colon, with the normal range stretching anywhere from 10 to about 59 hours. Anything that speeds up transit, or anything that adds its own strong pigment to the mix, can result in green stool.
Foods That Turn Stool Green
The most straightforward cause is simply eating a lot of green food. Spinach, kale, broccoli, avocados, herbs, matcha, and pistachios are all rich in chlorophyll, the same pigment that makes plants green. Eat enough of them and that pigment carries straight through to your stool.
Blue and purple foods can also produce green stool, which surprises people. Blueberries contain compounds called anthocyanins that can tint stool blue or green. Artificial food dyes in brightly colored frosting, drink mixes, ice pops, and candy do the same thing. When blue or purple dye mixes with the yellow-green bile already in your intestines, the result is a vivid green. This is especially common in kids who eat brightly colored treats.
Medications and Supplements
Iron supplements are one of the most reliable causes of dark green or even blackish-green stool. This is a well-known side effect and completely harmless. Some antibiotics can also tint stool yellow or green, partly because they disrupt the gut bacteria responsible for converting bile pigments to their usual brown color. If you’ve recently started a new medication and notice the change, the timing is probably not a coincidence.
Rapid Transit and Diarrhea
When food moves through your intestines faster than normal, bile doesn’t have enough time to fully break down. The green pigment that would normally be converted to brown simply passes through intact. This is why diarrhea from any cause, whether it’s a stomach bug, food intolerance, stress, or too much coffee, often comes out green.
Certain infections are particularly associated with green diarrhea. Bacterial infections like Salmonella and E. coli, viruses like norovirus, and parasites like Giardia can all cause a rapid “gush” of unabsorbed bile through the intestines. In these cases, the green color isn’t the problem itself. It’s just a visible sign that everything moved through too quickly for normal processing.
Digestive Conditions
Conditions that affect how well your body absorbs nutrients can also produce persistently green stool. Celiac disease and Crohn’s disease, for example, can interfere with fat absorption and speed up transit time, both of which leave bile pigments underprocessed. If your stool is consistently green over weeks and you haven’t changed your diet, a malabsorption issue is worth considering, especially if you’re also experiencing bloating, weight loss, or fatty-looking stools.
Green Stool in Babies
Green poop in infants is extremely common and rarely concerning. Breastfed babies may produce green stool if they don’t fully finish feeding on one side, which means they get more of the lower-fat foremilk and less of the higher-fat hindmilk. This changes how the milk is digested. Babies on hydrolyzed protein formula (used for milk or soy allergies) also tend to have greener stool. And because newborns are still building up their gut bacteria, breastfed infants may simply lack enough of the microbes needed to convert bile pigments to brown. As the baby’s digestive system matures, stool color typically shifts.
When Green Stool Signals a Problem
On its own, green stool is not a red flag. It becomes worth paying attention to when it shows up alongside other symptoms: persistent diarrhea lasting more than a few days, fever, blood or mucus in the stool, significant abdominal pain, or unexplained weight loss. Those combinations can point to an infection or an underlying digestive condition that needs evaluation.
If you can trace the color back to a spinach salad, a handful of blueberries, or a new iron supplement, you have your answer. The color should return to normal once that food or supplement works its way through, typically within one to three days.