Stress is a well-known cause of diarrhea but usually in the acute situation. For example, before a final examination a student may have the urge to have a bowel movement, and the bowel movement may be looser than usual.
Chronic diarrhea is less likely to be caused by stress. The relationship between stress and constipation has not been studied much. Since stress causes most things to be worse, it is possible that it also exacerbates constipation or at least the perception of it.
The major causes of troublesome constipation relate to muscular abnormalities of the colon and rectum, and these are not stress-related to the best of our knowledge.
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