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Stool Color Changes

Stool Color Overview

The color of stool normally is brown. The reason for the brown color is the presence of bile in the stool. Bile is made by the liver, concentrated and stored in the gallbladder, and secreted into the intestine to aid in the digestion of food. Depending on the amount of bile it contains, the normal stool color can range in color from light yellow to almost black.

Bile secreted from the gallbladder into the intestine is a very dark green liquid made up of many chemicals, one of which is bilirubin. When red blood cells are destroyed naturally in the body, hemoglobin, a protein inside the red blood cells that carries oxygen, is modified in the liver. The by-product of this process is bilirubin, and the liver secretes the bilirubin into bile.

As bile travels through the intestines, it can undergo further chemical changes, and its color can also change. For example, if the traveling time through the intestine is rapid, then bile won't have the time to go through additional color changes and the stool color may be close to green.

The color of stool can change for other reasons as well. Many changes in stool color may not be of much importance, especially if the change happens once and is not consistent from one stool to the next. Sudden major changes in stool color that persist may suggest an underlying medical problem. Furthermore, gradual but persistent changes in stool color also can signify medical problems.

Some of the important colors of stool that can signify problems include:

  • red
  • maroon
  • black
  • clay-colored
  • pale
  • yellow
  • green

Stool Color Changes Causes

Patient Comments

Stool color can change for a variety of reasons. The change may reflect substances that are added to stool, or changes to substances that normally are present in stool. Some stool color changes may suggest an underlying medical condition, and others may be due to ingestion of certain foods or medications.

Black Tarry, Sticky Stools

Bleeding in the stomach or the intestines can change the color of stool. If bleeding occurs in the stomach or the upper part of the small intestine, the stool may turn black and sticky, described medically as black, tarry stool (melena). Generally, black, tarry stool also is foul-smelling. This change in color and consistency occurs because of chemical reactions to blood within the intestine that are caused by digestive enzymes within the intestines.

Maroon or Red Stools

If the bleeding originates from lower parts of the intestines or the colon, blood may not come into prolonged contact with digestive enzymes because of the short distance from the site of bleeding to the rectum. Moreover, large amounts of blood within the intestines speed up transit of stool so that there is less time for the changes to take place. The stool in this type of bleeding may be dark red or maroon in color. Beets, other red vegetables, cranberries, and red food dyes also can turn the stool color red or maroon.

Black Stools (Not Sticky, No Odor)

Other causes of black stool are iron pills or bismuth-containing medications (such as, bismuth subsalicylate or Pepto-Bismol). If the stool color is dark because of any of these medications, it is typically not sticky in texture and is not foul-smelling .

Gray or Clay-Colored Stool

Stool can be gray or clay-colored if it contains little or no bile. The pale color may signify a condition (biliary obstruction) where the flow of bile to the intestine is obstructed, such as, obstruction of the bile duct from a tumor or gallstone in the duct or nearby pancreas. The change of stool color to gray or clay typically occurs gradually as these medical conditions progress relatively slowly and stool becomes pale over time.

Yellow Stool

Stool that is yellow may suggest presence of undigested fat in the stool.

This can occur as a result of diseases of the pancreas that reduce delivery of digestive enzymes to the intestines (pancreatic insufficiency), such as:

  • cystic fibrosis,
  • chronic pancreatitis (long standing inflammation and destruction of the pancreas usually due to alcohol abuse), or
  • obstruction of the pancreatic duct that carries the enzymes to the intestines (most commonly due to pancreatic cancer).

Celiac disease: Another condition that possibly may cause yellow and greasy stool is celiac disease (a malabsorption syndrome).

The digestive enzymes released from the pancreas and into the intestines are necessary to help digest fat and other components of food (proteins, carbohydrates) in the intestines so that they can be absorbed into the body. If the pancreas is not delivering enzymes into the intestines, then components of food, especially the fat, can remain undigested and unabsorbed. The stool containing the undigested fat may appear yellowish in color, greasy, and also may smell foul.

Ingestion of very high fatty foods also can cause yellow, soft, and foul smelling stools.

Weight loss medications such as orlistat (Xenical, alli) work by limiting the amount of fat absorbed by the intestines. This can lead to bulky, yellow, and greasy stools.

Green Stool

When stool passes through the intestines rapidly (diarrhea), there may be little time for bilirubin to undergo its usual chemical changes. Thus, stool can appear green in appearance due to rapid transit.

Excessive ingestion of green foods and vegetables also can cause stool color to turn more green than normal.

Medically Reviewed by a Doctor on 12/31/2014
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