What does dark stool mean?

Written by mary freeman
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What does dark stool mean?
Monitoring your stool is important for maintaining good health.

Dark bowel movements can be red, brown, grey or black. The cause of the stool darkening will determine the colour; however, most dark stool appears black.


Bilirubin, which is found in bile, undergoes many chemical changes as it passes through the digestive tract. These changes can account for the colour of stool, which is usually light or dark brown for normal processes or dark green when chemical changes have happened rapidly.


Duodenal, gastric and peptic ulcers can all cause stools to become black.


Tumours in the abdomen and intestines may cause intestinal bleeding leading to tarry, black stool. These tumours can also cause blockages keeping bilirubin from making it into the stool, which will cause grey, claylike bowel movements.


When bleeding occurs in the digestive tract, for any reason, stool will turn black due to the chemical changes to the haemoglobin flowing into the intestinal tract. If the bleeding is occurring in the lower intestines, than stools will appear red in colour.


High intake of iron from ingesting foods like beets or medicines such as bismuth subsalicylate or Pepto Bismol will harmlessly darken stool.

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