Changes in stool color are usually harmless and due to changes in diet. The normal color of stool is brown, which is due to a substance called bilirubin, which is a substance found in bile. As it passes through the intestines it changes from light to a dark brown color.
In some cases, change in stool color can be caused by medical conditions or medications. If your stool is:
- Green: This may occur when you have diarrhea and stool moves through the intestines too quickly. It can also be caused by eating green leafy vegetables or foods with green or purple food coloring.
- Black stool: This is usually foul-smelling and is caused by upper intestinal bleeding (stomach or upper small intestine, ulcers, or tumors. It may also be caused when you take iron supplements or bismuth (Pepto Bismol).
- Maroon or purple stool: This is caused by intestinal bleeding (usually in the small intestine or first part of the colon), ulcers, tumors, Crohn's disease, ulcerative colitis, or infections.
- Bright red stool: This occurs when bright red blood gets mixed with or covers the stool as it passes through the rectum. This is caused by hemorrhoids, colon polyps, anal fissures, massive gastrointestinal bleeding, or colon cancer.
- Clay-colored stool (amelanotic): This is caused when the bile duct from the liver and gallbladder is blocked. No bilirubin reaches the intestine to help break down your food and the stool does not change to its usual brown color.
- Pale yellow stool: This is usually greasy and foul smelling, and is caused by problems with the pancreas. These pancreatic disorders include pancreatitis, pancreatic cancer, and cystic fibrosis. It can also be caused by celiac disease.
Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care
UpToDate. Patient information: Peptic ulcer disease (Beyond the Basics).
UpToDate. Major causes of upper gastrointestinal bleeding in adults.
UpToDate. Overview of the medical management of severe or refractory Crohn's disease in adults.
UpToDate. Cystic fibrosis: Assessment and management of pancreatic insufficiency.