Stool color is generally 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.
Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
(feces) is most commonly brown in color, and many people become curious or
concerned when the color of their stool changes. 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
The color of stool is normally due to the presence of bile, specifically, the
bilirubin in bile. Bilirubin is formed from
hemoglobin after hemoglobin is
released from red blood cells during their destruction, a part of the normal
process of replacing the red blood cells in blood. The released hemoglobin is
modified chemically and removed from the blood by the
liver. In the liver the
chemically changed hemoglobin (called bilirubin) is attached to other chemicals
and secreted from the cells of the liver into bile. Depending on the
concentration of bilirubin, bile can vary from almost black to light yellow in
How do changes in bilirubin affect stool color?
Bilirubin travels with bile that is produced by the liver and then transported out of the liver by the bile ducts into the gallbladder, where it is stored until it is released into the intestines. (Bile is an important way for the liver to get rid of waste products such as bilirubin that are formed within the body.) As the bile and bilirubin pass through the intestines they are exposed to bacteria within the intestines. The bacteria can change the chemical nature of bilirubin, and this can change the color of stool.
If stool travels through the intestines at a normal speed, its color is a normal brown. Travel at a more rapid speed can result in chemical changes that may turn the stool green. Thus,
green stool by itself is only a sign of a change of the speed with which stool is traveling and not necessarily a sign of disease. On the other hand, if the entry of bile into the intestines is blocked, for example, by a tumor of the bile ducts or pancreatic cancer, the stool becomes
clay-colored. Clay-colored stool always is a sign of important disease.