Why is my poop green? Stool colors explained
Poop is generally brown, but, at times, it can turn green, red, black, yellow, or anything in between. Many of these color changes do not signal a medical condition, but some can be a sign of something more serious.
This article discusses poop color, what it means, and when to speak with a doctor.
Here are some key points about poop color. More detail and supporting information is in the main article.
- Certain foods and drinks can have significant effect on poop color
- Poop can turn green due to diarrhea
- Long-term changes to poop color should be examined by a doctor
Does green poop indicate illness? There are many reasons why stool can change color.
What makes poop green? Green stool is usually the result of a high quantity of leafy, green vegetables in someone's diet. Specifically, it is the chlorophyll in the plant that produces the green color. Alternatively, children might have green stool after attending a birthday party where they ate artificially colored frosting.
Diet-based reasons for green poop are by far the most common, but there are others; people who do not eat a lot of greens or food coloring should be wary, as green poop can have a more serious cause.
Bile pigment - stool may be green due to bile pigment in the stool. If food moves too quickly through the intestine, bile pigment can't break down sufficiently. One potential cause of this is diarrhea.
Antibiotics - a course of antibiotics changes the types of bacteria present in the gut. Because bacteria influence the normal color of poop, a change in bacteria may mean a change in stool color, often to green.
Certain medical procedures - for instance, if a bone marrow transplant is rejected, it can cause graft versus host disease. One of the consequences of this condition is diarrhea and green stool.
Parasites and bacteria - certain pathogens can cause poop to turn green, including the Salmonella bacterium, Giardia (a water-based parasite), and norovirus. These unwelcome guests can cause the guts to work faster than normal, 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 their doctor.
Image credit: Stephen Kelly, 2018
Factors of poop color
The normal color of stool should be a light to dark brown. A substance from red blood cells called bilirubin gets broken down and ends up in the intestines. Bacteria then break it up and turn it brown.
So, what does it means when the color of poop suddenly changes, and what are some of the possible causes?
Changes in diet can produce varying stool colors; this is the most common cause. Eating beets, green vegetables (because of the high chlorophyll content), or licorice can significantly change the color of stool. Drinking Guinness or drinks that contain heavy dye such as Kool-Aid can have a similar effect.
There are, however, more serious causes of non-brown stool color which should be dealt with immediately if discovered.
Here is a brief list of potential illnesses that may change the color of stool:
- Tears in the lining of the anus
- Gallbladder disease
- Celiac disease
- Ulcerative colitis - a condition where the top layer of the large intestine lining is inflamed
- Crohn's disease - a condition where all of the large intestine can become inflamed
- Diverticular disease - a condition where pouches form in the intestine
- Infections - bacteria and parasites can change stool color; for instance, Salmonella and Giardia can both lead to green stools
- Piles (hemorrhoids)
- Bleeding in the gut
It is difficult to consistently relate a precise color to each illness. However, there are some general characteristics that can serve as a guide.
- Reddish stool - can be caused by bleeding in the lower gut or rectum.
- Yellowish, greasy, smelly stool - 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, celiac disease for instance.
- White, light, or clay-colored - this can indicate a lack of bile in the body, possibly from a blocked bile duct. Certain medications can also cause this discoloration, such as bismuth subsalicylate (e.g. Pepto-Bismol) and other anti-diarrheal medication.
- Black or dark brown - could indicate bleeding in the upper digestive tract, for instance, the stomach. Alternatively, it could be caused by iron supplements or bismuth subsalicylate.
- Bright red - bleeding in the lower digestive tract (rectum, for instance) or, commonly, hemorrhoids. Alternatively, it may be due to red food coloring, cranberries, beets, tomato-based products, red gelatin, or drinks with red food coloring.
- Green - eating large quantities of green dye, green vegetables; a course of antibiotics, or a bacterial infection.
It is important that people see a doctor if any discoloration persists instead of trying to work it out for themselves.
It is important to know what to look out for regarding the more serious causes of stool discoloration. These can include conditions such as diverticulitis, Crohn's disease, and cancer, which usually manifest with bleeding from the anus.
Important symptoms to look out for include:
- Dark, tarry stools
- Large amounts of blood passed from the rectum
- Blood in the toilet bowl
- 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 end of the bowel and the skin of the anus
As well as any traces of blood in the stool, or general bleeding from the anus, pay attention to any other symptoms linked with stool discoloration. These include light-headedness, dizziness, nausea, or vomiting, especially if vomit contains blood as well.
Inflammation of the gut can lead to rectal bleeding.
People should seek the advice of a doctor immediately if any of these symptoms persist. Common causes of rectal bleeding include:
- Piles (hemorrhoids)
- Tears in the lining of the anus
- Anal fistula - a small channel that develops between the end of the bowel and the skin of the anus
- Angiodysplasia - swollen blood vessels in the gut
- Gastroenteritis - inflammation of the gut
- Diverticular disease
- Bowel cancer (colon or rectal cancer)
Less common causes of rectal bleeding include:
- Drugs that treat blood clots
- Inflammatory bowel disease
- Bowel polyps - small growths that are usually harmless
- Sexually transmitted infections (STIs)
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. If there are any illnesses occurring in the body such as those mentioned above, stool may give a clue.
According to the Bristol Stool Chart, there are seven shapes and formations that characterize our stool. Each one denotes something about a person's diet or body.
The Bristol Stool Chart
- Type 1: Separate, hard lumps, like nuts (that are 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 pieces with ragged edges, mushy
- Type 7: Watery, no solid pieces (entirely liquid)
As a general rule, type 3 or 4 is the ideal stool as it is easy to pass without being 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, as well as measure the time it takes for food to pass through the digestive system. The shape and form of stool may also help doctors to make a correct diagnosis.
The most important thing to do to regulate stool color is to eat healthily. As discussed earlier, the ideal stool color is light to dark brown. Some people who have a high quantity of greens in their diet may pass poop that has a green color too.
Having green poop isn't usually a cause for concern. However, it is important for people to keep an eye on both the color and the texture of their stool. Anyone who is concerned about the color of their stool should discuss it with their doctor.