Stool is naturally brown due to the digestion of bile salts produced by the liver and blood pigments such as bilirubin. Dietary supplements including iron, medications, and some foods, such as blueberries, beets, or black licorice, can darken the stool or even turn it black.
Dark stool, when not associated with diet, supplements or medications, can be a worrisome symptom, as it can be due to bleeding in the digestive tract.
The color of bloody stool depends on the site of the bleeding and how quickly food moves through the digestive system. Blood from the esophagus, stomach, and small intestine may have time to be digested, resulting in dark, tarry stool.
Red blood in the stool frequently comes from the lower portion of the digestive tract, specifically the colon or anus. However, bleeding from a higher portion of the digestive tract can speed digestive transit, also leading to red stool.
Red striping of the stool is often related to bleeding of the rectum or anus and may be seen in stool of people who have hemorrhoids (inflamed veins in lower rectum or anus).
Pale stool can occur if bile salt production is reduced or its transport is blocked due to serious liver infections or a bile duct obstruction that is caused by stones, scarring, abnormal development, or external compression.
Liver disease and bile duct obstruction can also cause jaundice, a yellowing of the skin and whites of the eyes that may be accompanied by itching.
Changes in stool color can be related to diet, supplements or medications; however, stool that is persistently dark or light can be an indication of a serious medical problem.
Seek immediate medical care (call 911) for bloody stool, which may be red or black or tarry in consistency, and may be accompanied by severe pain, profuse sweating, alterations in level of consciousness, rapid heartbeat (tachycardia), vomiting blood, or chest pain.
If your stool color changes are persistent or cause you concern, seek prompt medical care.
What is the color of normal stool?
Stool (feces) color is most commonly brown. When stool color changes, often, an individual becomes concerned. The presence of the bilirubin in bile is generally responsible for stool color. Bilirubin concentration can vary bile color from light yellow to almost black in color.
Changes in bilirubin can cause stool to turn green, gray, or clay-like in color. Intestinal bleeding may turn stool black, tarry, red, maroon, or smelly stool. Medication and food may also affect stool color.
Most stool-to-stool changes in color have little meaning; however, some changes, particularly if the changes are consistent from stool-to-stool and not present in only one stool, can be important.
What are the symptoms of stool color changes?
Symptoms of stool color changes do not cause symptoms in most cases.
Symptoms that may occur with changes of stool color are a result of the underlying cause of the change in stool color. For example:
- Diarrhea may produce green stools caused by a number of reasons.
- Abdominal pain may produce clay-colored stools.
- Back pain may signal a tumor blocking the bile ducts.
- Upper or lower abdominal pain (sometimes caused by bleeding in the GI tract.
- Nausea and vomiting associated with stool color changes may be from heavy associated bleeding.
If stool passes through the intestine too quickly, there might not be enough time for bile to be digested and broken down to provide the normal brownish stool color. Bile is a greenish brown fluid that is manufactured in the liver and stored in the gallbladder.
Bile helps digest fats in food. It takes time for the bile to degrade and turn brown in the intestine and if the transit time is short, the stool remains green colored. This is why diarrhea is often greenish in color.
Green stools may be a normal variant. It can also be caused by a diet rich in green vegetables, especially spinach. Iron supplements also may be a cause, though it often turns stool black.
Yellow, greasy, and foul smelling stool
There are a variety of reasons why stool will be yellow and greasy appearing. It can be due to the intestine’s inability to digest fat because of malabsorption such as in celiac disease and cystic fibrosis, or because the pancreas is unable to manufacture adequate digestive enzymes.
Yellow poop can be caused by gastrointestinal infection caused by giardiasis, a protozoan infection that can cause significant diarrhea.
Black tarry stools
Black stools are a worrisome symptom because it may be due to bleeding into the gastrointestinal tract, most often the esophagus, stomach or duodenum. Red blood cells are broken down by digestive enzymes and turn the stool black. These stools tend to be tarry and foul smelling.
This can be a medical emergency; black tarry stools should not be ignored.
Blood from nosebleeds or from dental procedure and injuries can be swallowed and may be the cause of black stool.
Certain foods and medications can turn stool black, including iron, bismuth (Pepto Bismol, loperamide [Kaopectate]), beets, and licorice. While the stools may be black, they also tend to be gritty and not tarry.
Bright red stools
The most common cause of bright red stool is bleeding from hemorrhoids, but other bleeding causes are much more significant. For that reason, blood in the stool should never be ignored.
Other causes include infection, inflammatory bowel disease (Crohn’s disease, ulcerative colitis), diverticular bleeding, tumors, and arteriovenous malformations (AVM). Brisk bleeding from the upper GI tract may cause stools to be red instead of black because there has not been enough time for the red blood cells to be digested.
Red food coloring and beets can also give a reddish hue to the stool.
Light-colored white or clay-colored stools
White or clay colored stool are often seen with liver or biliary tract diseases. Lack of bile which gives stool its brown color leaves the poop appearing pale.
Maroon colored stools are often due to bleeding in the GI tract. Classically, the source of bleeding for black tarry stools is the upper GI tract (esophagus, stomach, duodenum), while the colon is the source for bright red blood.
Maroon stools may arise from the small intestine (jejunum, ileum) and proximal colon, but these are not hard and fast rules.
How bright the red color is depends not only upon the location of bleeding, but also how quickly the blood moves through the intestine. The faster the stool moves through the GI tract, the brighter red the color. This can be an emergency situation.
Mucous in the stool
Mucous in the stool may be a normal variant, and it may cover segments of formed feces. However, it also can occur in patients with inflammatory bowel disease or cancer.
Mucous that is also associated with blood and/or abdominal pain should not be ignored and requires medical attention. Mucous in stool can also be seen in patients with irritable bowel syndrome.
Stool that floats
Most stool floats because of poor absorption of nutrients or excess flatus (gas). It is a normal variant and usually of no concern.
Changes in diet can lead to stool that floats, but as an isolated symptom, no action needs to be taken and often it resolves spontaneously.
Malabsorption syndromes that are associated with floating stool include lactose intolerance, celiac disease, cystic fibrosis, and short bowel syndrome.
Stool does not float because of increased fat content.
What causes stool color?
Stool color is due to digestion of bile salts produced in the liver and can be influenced by diet, medications or supplements. Bleeding in the digestive tract can cause red, dark or black stool.
Liver problems and conditions causing obstruction of the bile ducts can cause pale stools.
Foods, medications, and supplement causes of stool color changes
Dark brown, bluish, reddish, or black stool color may be caused by foods, medications, and supplements including:
- Black licorice
- Iron supplements
- Medications containing bismuth subsalicylate (Kaopectate, Pepto-Bismol)
How is the cause of stool color changes diagnosed?
In most cases, a diagnosis cannot be made by stool color alone.
The patient and the doctor need to consider other symptoms, past medical history, dietary changes, and medications to help decide what has caused the stool to change color. Physical examination will be important to help decide the significance of the stool color.
Stool may be tested to look for blood, fat or infection. Blood tests may be necessary depending upon the clinical situation.
What are the potential complications of stool color?
Because changes of stool color can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage.
Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:
- Anemia (low red blood cell count)
- Intestinal obstruction and rupture of the intestinal wall
- Poor nutrition due to diarrhea or a decreased desire to eat
- Spread of cancer
- Spread of infection
Surgery to remove parts of the digestive tract due to serious infection or malignant condition