Green poop is usually not a sign of a health problem.
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It may be alarming to see green poop in your toilet bowl, but it isn't necessarily a cause for concern.
The color of your stools is often a reflection of what you eat. Black stools, for example, can result from eating blueberries or taking medications that contain bismuth subsalicylate, such as Pepto-Bismol.
Your poop may be green if you eat a lot of green vegetables, such as spinach and broccoli, because these foods contain large amounts of the green pigment chlorophyll.
Other dietary causes for green stool are iron supplements and green food coloring, which can be found in flavored drink mixes, ice pops and birthday-cake icing.
Bile — a fat-digesting yellow-green fluid that's secreted by the liver and stored in the gallbladder — can also cause green poop.
"As bile pigments travel through your gastrointestinal tract, they are chemically altered by enzymes, changing the pigments from green to brown," gastroenterologist Dr. Michael F. Picco explained on Mayo Clinic's website.
However, if food is moving through your large intestine too quickly, the bile doesn't have time to break down completely and stains your stool green, rather than brown.
Sometimes, green poop is an indication of a health issue. For example, cancer patients who undergo a donor bone-marrow transplant may develop graft-versus-host disease, which is marked by a number of gastrointestinal symptoms, including watery, green diarrhea, according to the National Cancer Institute.
Certain infections, like those caused by the bacterium Salmonella or the parasite Giardia, can also cause green stool. But other symptoms — including severe diarrhea, abdominal cramps and fever — are common with these illnesses.
In short: Green stool is typically benign and not something you need to worry about, unless it's accompanied by symptoms of other health problems.