Green poop is almost always harmless. In most cases, it simply means you ate something green or that food moved through your digestive system a little faster than usual. Occasionally, though, green stool that lasts more than a few days or comes with diarrhea, fever, or cramping can signal an infection worth checking out.
Why Stool Is Normally Brown
Your liver produces bile, a green fluid that helps you digest fats. As bile travels through your digestive tract, enzymes chemically break it down and gradually shift its color from green to brown. That process takes time. If everything moves at a normal pace, your stool comes out brown. If transit speeds up for any reason, bile doesn’t fully break down, and the green color carries through to the toilet bowl.
Foods That Turn Stool Green
This is the most common explanation. Chlorophyll, the pigment that makes plants green, can do the same to your stool. Spinach, kale, and broccoli are frequent culprits, but the list also includes avocados, fresh herbs, matcha, and even pistachios (which get their green color from the same pigment). The more of these foods you eat in a sitting, the more vivid the result.
Artificial food dyes are another common cause. Brightly frosted cupcakes, green sports drinks, candy, and ice cream can all tint your stool shades that look alarming but are completely benign. The dye simply continues coloring whatever it touches as it passes through.
If a food or dye is the cause, your stool color typically returns to normal within a day or two after you stop eating it. There’s nothing you need to do in the meantime.
Supplements and Medications
Iron supplements are well known for turning stool dark green or even black. This is a harmless side effect of unabsorbed iron and not a reason to stop taking them. Some antibiotics can also shift stool toward green or yellow by disrupting the balance of gut bacteria that normally help process bile pigments. If the color change started around the same time as a new medication, that’s likely the connection.
Infections That Cause Green Stool
Bacterial infections like Salmonella and E. coli, viral infections like norovirus, and parasites like Giardia can all produce green diarrhea. The mechanism is straightforward: these infections speed food through your intestines so quickly that bile has no time to change color. You’ll almost always have other symptoms too, including watery diarrhea, cramping, nausea, or fever.
Antibiotic-associated infections can also be responsible. In a small case series, 80% of stool specimens from patients with a particular antibiotic-related bacterial infection were greenish. The takeaway isn’t to panic, but to pay attention if green stool and diarrhea develop during or shortly after a course of antibiotics.
Green Stool in Babies
Green poop in newborns and infants is especially common and rarely a concern. Meconium, a baby’s first stool, is naturally dark green to black. After that transition period, several things can keep stool green:
- Foremilk/hindmilk imbalance: If a breastfed baby doesn’t finish nursing on one side, they may get less of the higher-fat hindmilk. This affects how the milk is digested and can produce green stool.
- Specialty formula: Protein hydrolysate formulas, used for babies with milk or soy allergies, often produce green or dark green stool.
- Developing gut bacteria: Breastfed infants sometimes lack the full range of intestinal bacteria that help process bile, so green tones are normal as their microbiome matures.
- Diarrhea: Just like in adults, faster transit means greener stool.
For babies, the bigger concern is always hydration rather than color. Frequent watery stools that soak through diapers matter more than the shade.
When Green Stool Needs Attention
A single green bowel movement, or even a couple of days of green stool after a big salad or a course of antibiotics, is not a problem. The Mayo Clinic recommends contacting a healthcare professional if green stool persists for more than a few days without an obvious dietary explanation.
Green stool paired with diarrhea deserves closer attention because dehydration is the real risk. If you’re also experiencing fever, bloody stool, severe abdominal pain, or signs of dehydration like dizziness, dark urine, or dry mouth, those symptoms together point toward an infection or another condition that benefits from evaluation. The green color alone, without these accompanying signs, is almost never the problem.