Irritable Bowel Syndrome Home > Irritable Bowel Syndrome Causes

Although there has been a significant amount of research done, the cause or causes of irritable bowel syndrome (IBS) are unknown. However, researchers do know that the motility of the colon in people with IBS may not work properly. Also, in people with IBS, the colon responds strongly to certain stimuli (such as foods or stress) that would not bother most people.

What Causes Irritable Bowel Syndrome?

At this point, no one knows the exact cause or causes of irritable bowel syndrome (IBS). Genetics and the environment are thought to play a role. Some evidence indicates that the immune system, which fights infection, is also involved. Yet, despite a huge amount of research, the exact reason for IBS remains unknown.

What Is Known About Irritable Bowel Syndrome?

While it is not known what causes IBS, researchers do know a lot about this digestive condition. For example, they know that:
  • The normal motility of the colon may not work properly in people with IBS. It can be spasmodic or can even stop temporarily. Spasms are sudden, strong muscle contractions that come and go.
  • With IBS, the lining of the colon (epithelium), which regulates the passage of fluids into and out of the colon, may become overwhelmed by the fast movement of the colon's contents. This can affect its ability to absorb fluids. The result is too much fluid in the stool. In other people, colonic movement is too slow and too much fluid is absorbed, resulting in constipation.
  • In people with IBS, the colon responds strongly to stimuli (for example, foods or stress) that would not bother most people.
  • In people with IBS, stress and emotions can strongly affect the colon. It has many nerves that connect it to the brain. Like the heart and the lungs, the colon is partly controlled by the autonomic nervous system, which has been proven to respond to stress. 
For example, when you are frightened, your heart beats faster, your blood pressure may go up, or you may gasp. The colon responds to stress as well. It may contract too much or too little, or it may absorb too much or too little water.
It is unlikely however, that stress or anxiety actually cause irritable bowel syndrome.
  • Some people get irritable bowel syndrome after a severe infection in the gastrointestinal (GI) tract. Researchers aren't sure how the infection causes IBS. They do know that most people with IBS never had a severe gastrointestinal infection.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
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