Green poop is almost always harmless. In most cases, it means you ate something with a lot of green pigment, you’re taking a supplement that changes stool color, or food moved through your digestive system faster than usual. Occasionally, green stool points to an infection or other digestive issue worth paying attention to.
How Stool Gets Its Color
Normal stool is brown because of a pigment called bilirubin. Your liver produces bile, which starts out yellow-green, and as it travels through your intestines, bacteria break it down into that familiar brown color. The process takes time. Average transit through the colon alone is 30 to 40 hours, and anything up to about 72 hours is still considered normal.
When something interrupts that process, whether it’s a pigment from food overriding the brown, a supplement altering the chemistry, or food rushing through too quickly for bile to fully break down, the result can be green stool.
Foods That Turn Stool Green
The most common cause is simply eating a lot of green vegetables. Spinach, kale, and broccoli are packed with chlorophyll, the pigment that makes plants green, and your body doesn’t always fully break it down during digestion. Eat enough of these and the green pigment passes straight through. Avocados, fresh herbs, pistachios, and matcha (powdered green tea) can do the same thing.
Artificial food dyes are another frequent culprit. Blue and green dyes used in candy, ice cream, frosting, sports drinks, and brightly colored cereals can produce surprisingly vivid green stool. Purple or blue dyes can also mix with the yellow-green of bile and come out looking green. If you recently ate something with intense coloring, that’s likely your answer.
Iron Supplements and Medications
Iron supplements are well known for changing stool color. They typically turn stool dark green to black, which catches people off guard. This happens because iron reacts with digestive enzymes as it passes through your gut. The color change is a normal side effect and not a sign that anything is wrong, as long as you’re taking iron intentionally.
Some antibiotics can also cause green stool by disrupting the balance of gut bacteria. Since those bacteria are responsible for converting bile pigments to brown, killing them off temporarily changes the equation. Bismuth-containing medications (the active ingredient in some stomach remedies) can have a similar darkening effect.
When Food Moves Too Fast
If nothing you’ve eaten recently explains the color, the cause may be speed. When food passes through your intestines faster than normal, bile doesn’t have enough time to be fully broken down by bacteria. The result is stool that retains bile’s original green tint.
This can happen during a bout of diarrhea from any cause: a stomach virus, food poisoning, stress, or a food intolerance like lactose sensitivity. It can also happen after eating a very large meal or drinking a lot of caffeine. If the green color shows up alongside loose or watery stool, rapid transit is the most likely explanation. Once your digestion returns to its normal pace, the brown color comes back.
Infections and Digestive Conditions
Certain bacterial infections, particularly from Salmonella, Giardia, or E. coli, can cause persistent green diarrhea. These infections speed up transit time dramatically and can also trigger excess bile secretion. The green stool in these cases typically comes with other noticeable symptoms: cramping, nausea, fever, or stool that’s watery for more than a couple of days.
Conditions like Crohn’s disease, celiac disease, and irritable bowel syndrome can also occasionally produce green stool, usually because they affect how well nutrients and bile are absorbed. But in these cases, green stool would rarely be the only symptom. You’d typically also notice ongoing changes in bowel habits, abdominal pain, or unintentional weight loss.
Green Stool in Babies
Green poop in infants is extremely common and usually not a problem. In breastfed babies, green, frothy, or explosive stools can happen when milk moves through the baby’s system too quickly for all the lactose to be digested. Fat in breast milk helps slow digestion and gives the baby’s gut more time to process lactose. When feeds are short or milk supply is very abundant, the baby may get less of the higher-fat milk, causing the lactose to pass through only partially digested.
This was traditionally explained as a “foremilk/hindmilk imbalance,” but the current understanding is that fat content in breast milk changes gradually throughout a feeding rather than switching suddenly. The practical takeaway is the same: allowing the baby to feed longer on one breast before switching can help. Formula-fed babies also get green stool occasionally, often from iron-fortified formula, and it’s equally harmless.
When Green Stool Needs Attention
A single green bowel movement, or even a few days of green stool after eating a big salad or starting an iron supplement, is nothing to worry about. The color alone is not a warning sign.
Green stool becomes worth investigating when it lasts more than a few days without an obvious dietary explanation, or when it’s accompanied by other symptoms like persistent diarrhea, fever, significant abdominal pain, or mucus in the stool. Bright red or black stool (not explained by iron or bismuth) is a more urgent concern, as these colors can indicate bleeding in the digestive tract and should be evaluated promptly.
For most people who glance down and see an unexpected shade of green, the answer is somewhere in their recent meals, a supplement they started, or a temporary change in how quickly things moved through. It resolves on its own once the trigger is gone.