Stool Color (cont.)

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How does intestinal bleeding change stool color?

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One important internal process that can change the color of stool is bleeding into the intestines. The stool may turn black because of chemical changes to the hemoglobin in blood caused, in part, by the action of intestinal enzymes, particularly if bleeding is more rapid and there is a large amount of hemoglobin within the intestines. A color change to black also is more likely if the bleeding occurs in the upper intestine since there is more time for the chemical changes to the hemoglobin to take place as the blood travels through the intestines.

Stool that is black due to bleeding is also "sticky" (tarry) and smells bad. These latter characteristics help distinguish black stools due to internal bleeding from black stools due to the ingestion of iron or bismuth-containing medicines, for example, bismuth subsalicylate (Pepto Bismol).

On the other hand, bleeding that occurs lower in the intestines, particularly in the colon, is likely to cause red or maroon-colored stools since there is little time for chemical changes to the hemoglobin to take place.

What other things can cause changes in the color of stool?

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Another internal process that may change the color of stool but that is less common than bleeding is pancreatic disease. The pancreas secretes enzymes into the intestines that help with the digestion of fat, protein, and carbohydrates. When pancreatic enzymes are not present in the intestine, fat is not fully digested. If the content of undigested fat is high enough, stool may become a yellowish color. The stool also appears "greasy" and smells bad. The most common pancreatic diseases that cause this are pancreatic tumors that block the pancreatic duct through which the enzymes reach the intestines and chronic pancreatitis, usually due to damage from excessive ingestion of alcohol, that destroys the ability of the pancreas to make enzymes. If there is both blood and undigested fat in the stool, the stool may become silver.

Several ingested substances can change the color of stool. Iron and bismuth-containing medications, for example, Pepto Bismol, turn the stool black. Beets and possibly some other red vegetables and fruits can turn stool a reddish color. Food dyes used for coloring foods also may color the stool.

Medically Reviewed by a Doctor on 3/7/2013

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Stool Color & Texture Changes - Personal Experience Question: What color is/was your stool? Please share your symptoms and experience.
Stool Color & Texture Changes - Causes Question: If your stool changed color, what was the cause? Did you receive a diagnosis from a doctor?
Stool Color Changes - Intestinal Bleeding Question: What part of your GI tract was bleeding, and what was the cause?