Dark green poop is almost always harmless. The most common causes are eating chlorophyll-rich foods, taking iron supplements, or having food move through your digestive system faster than usual. In most cases, your stool color will return to its normal brown within a day or two once the trigger passes.
How Stool Gets Its Color
Your liver produces bile, a yellowish-green fluid that helps digest fats. As bile travels through your intestines, bacteria break it down and gradually change its color from green to yellow to brown. That final brown shade is what most people see on a regular day. When something disrupts that process, whether it’s what you ate or how fast food is moving through you, the green pigment sticks around instead of completing its transformation.
Foods That Turn Stool Green
Chlorophyll is the pigment that makes plants green, and it can do the same to your stool. If you’ve been eating a lot of spinach, kale, broccoli, avocados, pistachios, fresh herbs, or matcha, that’s likely your answer. The chlorophyll passes through your digestive tract and tints everything along the way. The more you eat, the deeper the green.
Artificial food coloring can also be responsible. Brightly colored frosting, flavored drink mixes, ice pops, and candy contain dyes that keep tinting whatever they touch even after you swallow them. Blue and green dyes are especially common culprits, and sometimes blue dye mixed with yellow bile produces a surprisingly vivid green.
Iron Supplements and Medications
Iron supplements are one of the most common causes of dark green stool, sometimes so dark it looks almost black. This is a normal reaction to the iron and some physicians actually consider it a sign that the supplement is being absorbed properly. If the color bothers you, lowering your dose with your doctor’s guidance will typically lighten things up.
Certain antibiotics can also shift stool color toward green or yellow. This happens because antibiotics alter the gut bacteria responsible for breaking down bile. The effect is temporary and resolves once you finish the course of medication.
Rapid Digestion and Diarrhea
When food moves through your large intestine faster than normal, bile doesn’t have enough time to fully break down. It stays green instead of turning brown. This is why diarrhea often comes out greenish, regardless of what you ate. Anything that speeds up transit, from a stomach bug to stress to a strong cup of coffee on an empty stomach, can produce this effect.
Bacterial infections like Salmonella and E. coli, viral infections like norovirus, and parasites like Giardia all cause rapid-transit diarrhea that can look distinctly green. In these cases, the color itself isn’t the problem. What matters is whether you also have fever, severe cramping, blood in your stool, or diarrhea lasting more than a couple of days. Those symptoms together point to an infection that may need treatment.
Green Stool in Babies
A newborn’s very first stool, called meconium, is sticky and greenish-black. This is completely normal and clears within the first few days of life. After that transition, green poop in babies usually comes down to feeding.
Breastfed babies sometimes produce bright, frothy green stool. This often happens when the baby gets more of the thinner, watery milk at the start of a feeding (foremilk) and less of the richer milk that comes later (hindmilk). Feeding from one breast at a time until it’s fully drained can help balance this out. For formula-fed babies, green stool is commonly caused by iron-fortified formula, and it’s nothing to worry about.
How Long It Lasts
If food is the cause, your stool color will return to brown within one to three days after you stop eating the trigger food. Iron supplements will keep producing dark green stool for as long as you take them. For diarrhea-related green stool, the color normalizes once your digestion slows back to its usual pace.
Green stool on its own, without other symptoms, is rarely a sign of anything serious. The situations worth paying attention to are when green stool comes alongside persistent diarrhea, visible blood or mucus, significant abdominal pain, or fever. That combination suggests your body is fighting an infection or dealing with inflammation that may need medical attention.