Poop can turn green for many reasons. Some examples include a diet rich in high chlorophyll plants, such as spinach or kale, a course of antibiotics, or a bacterial infection. Although it is rarely a cause for concern, a change in poop color is worth investigating.

Poop is generally brown, but, at times, it can turn green, red, black, yellow, or any color in between. Many of these color changes do not signal a medical condition, but some can be signs of something more serious.

This article discusses poop color, what it means, and when to speak with a doctor.

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Infographic by Stephen Kelly

What makes poop green? Green stool is usually the result of eating a large quantity of leafy, green vegetables. Specifically, the chlorophyll in the plants produces the green color. Alternatively, children might have green stool after eating artificially colored frosting at a birthday party.

Certain foods in a person’s diet are by far the most common causes of green poop. However, people who do not eat a lot of greens or food coloring should be wary, as green poop can have a more serious cause.

Possible causes include:

  • Bile pigment: Stool may be green due to the presence of bile pigment. If food moves too quickly through the intestine, bile pigment cannot break down sufficiently. One potential cause of this is diarrhea.
  • Antibiotics: Antibiotics can change the types of bacteria present in the gut. Because bacteria influence the typical color of poop, a change in bacteria may mean a change in stool color, often to green.
  • Certain medical procedures: For instance, a person whose body rejects a bone marrow transplant may develop graft-versus-host disease. Diarrhea and green stool are symptoms of this condition.
  • Parasites and bacteria: Certain pathogens can cause poop to turn green, including the Salmonella bacterium, the water-based parasite Giardia, and norovirus. These unwelcome guests can cause the guts to work faster than usual, impacting stool color.

People who think their green stool is not the result of a diet rich in vegetables or green food coloring should discuss it with a doctor.

Stool is usually light to dark brown. A substance from red blood cells called bilirubin gets processed and ends up in the intestines. Bacteria then break it down further, and it turns stool brown.

So, what does it mean when the color of poop suddenly changes, and what are some possible causes?

Changes in diet can produce varying stool colors. Eating beets, high chlorophyll green vegetables, or licorice can significantly change stool color. Drinking Guinness or drinks that contain heavy dye, such as Kool-Aid, can have a similar effect.

In infants, foods may cause color changes, such as:

  • Green: spinach, breastmilk, formula
  • Red: beets, tomato soup, cranberry juice or other red drinks
  • Black: licorice, grape juice

However, some causes of non-brown stool are more serious, and it is important to deal with these issues immediately.

Health conditions that may change the color of stool include:

  • tears in the lining of the anus
  • gallbladder disease
  • celiac disease
  • ulcerative colitis, a condition in which typically only the luminal layer inside the large intestine lining is inflamed
  • Crohn’s disease, a condition in which all layers of the small and large intestines can become inflamed
  • cancerous tumors in the GI tract
  • cancers of other digestive organs
  • diverticular disease, a condition in which pouches form in the large intestine
  • bacterial or parasitic infections — for instance, Salmonella and Giardia can both lead to green stools
  • piles, also known as hemorrhoids
  • bleeding in the gut

It is difficult to consistently relate a precise color to each condition. However, here are some possible connections between colors and conditions:

  • Reddish or maroon: This can be a sign of bleeding somewhere in the GI tract.
  • Yellowish, greasy, smelly: This can indicate an infection in the small intestine. It could also be a sign of excess fat in the stool due to a malabsorption disorder, such as celiac disease.
  • White, light, or clay-colored: This can indicate a lack of bile in the body, possibly from a blocked bile duct. Certain medications, such as bismuth subsalicylate — e.g., Pepto-Bismol — and other antidiarrheal medications, can also cause this discoloration.
  • Black or dark brown: This can be a sign of bleeding in the upper GI tract, such as the stomach. Alternatively, it could be the result of iron supplements or bismuth subsalicylate.
  • Bright red: Bleeding in the lower digestive tract, such as the rectum, or hemorrhoids, which are also called fissures, may cause bright red stool. Alternatively, red stool may be due to consumption of red food coloring, cranberries, beets, tomato-based products, or red gelatin.
  • Green: Large quantities of green dye or green vegetables, antibiotics, or a GI tract infection may cause green stool.

If any discoloration persists, it is important that a person see a doctor instead of trying to work it out on their own.

The more serious possible causes of stool discoloration include conditions such as diverticulitis, Crohn’s disease, ulcerative colitis, and cancer, which usually manifest with bleeding from the lower GI tract.

Important symptoms to look out for include:

  • dark, tarry stools
  • red or maroon stools
  • large amounts of blood passed from the rectum
  • blood in the toilet bowl
  • an itchy anus
  • swollen blood vessels in the rectum
  • small tears in the skin of the anus
  • an urge to keep passing stools even when the bowel is empty
  • a small channel developing between the distal end of the large bowel and the skin near the anus

In addition to any traces of blood in the stool or bleeding from the anus, pay attention to any other symptoms that occur with stool discoloration. These may include nausea, vomiting blood, or a feeling of fullness.

A person should seek the advice of a doctor immediately if any of these symptoms persist.

Common causes of rectal bleeding include:

  • piles, as known as hemorrhoids
  • inflammatory bowel disease
  • tears in the lining of the anus, also known as fissures
  • anal fistula, a small channel that develops between the inside of the anus and the skin near the anus
  • gastroenteritis, which is inflammation of the gut
  • diverticular disease
  • bowel cancer, such as small intestine or colorectal cancer

It is worth having a quick look at stool before flushing it away. Stool is a very good indicator of whether the digestive system is working properly. It may provide a clue to illnesses such as those mentioned above.

According to the Bristol Stool Chart, there are seven shapes and consistencies of human stool. Each one denotes something about a person’s diet or body.

The Bristol Stool Chart

  • Type 1: separate, hard lumps, similar to nuts — often hard to pass
  • Type 2: sausage-shaped but lumpy
  • Type 3: sausage-shaped but with cracks on the surface
  • Type 4: sausage- or snake-like, smooth and soft
  • Type 5: soft blobs with clear-cut edges — easy to pass
  • Type 6: fluffy, mushy pieces with ragged edges
  • Type 7: watery with no solid pieces — entirely liquid

As a general rule, type 3 or 4 is the ideal stool, as it is easy to pass but not too watery. Type 1 or 2 means that a person is probably constipated. Type 5, 6, or 7 indicates that a person probably has diarrhea.

This chart helps doctors identify problems and correlate the time food takes to pass through the digestive system. The shape and form of stool may also help doctors make a correct diagnosis.

The most important thing to do to regulate stool color is to eat a healthy diet. The ideal stool color is light to dark brown. Some people who eat large quantities of greens may pass green poop.

Having green poop isn’t usually a cause for concern. However, it is important to keep an eye on both the color and the texture of stool. Anyone who is concerned about the color of their stool should discuss it with a doctor.

Learn more about how the Squatty Potty may improve bowel movements.

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