What Causes IBS?

The cause of IBS is not completely understood. In IBS, the digestive system appears normal on routine tests. For this reason, it has been referred to as a functional gastrointestinal (GI) disorder. However, there is increasing evidence that the GI symptoms experienced in IBS may be caused by one of more of the following:

  • Abnormalities in gut motility
  • Improper functioning of the immune system (over or under active)
  • Abnormal amounts of bacteria and other organisms (like viruses and fungi) in the gut (microbiota)
  • The central nervous system’s interpretation of painful signals coming from the gut.

Some of these factors may be more relevant in one individual with IBS, while other factors may be more important in another.

Brain-gut interactions

The Gut-Brain Axis (GBA) is a communication system between the digestive tract and the brain. This pathway is bi-directional, meaning the brain communicates with the gut, and the gut also communicates information to the brain.

When the Gut-Brain Axis (GBA) is out of balance, normal sensations—such as food moving through the digestive tract—that would typically not be noticed or considered bothersome, can be experienced as unpleasant symptoms. In other words, the gut can be more sensitive than normal.

Learn more about IBS and the Gut-Brain Axis

Does bacteria cause IBS?

There are trillions of bacteria in the gastrointestinal (GI) tract. These bacteria help break down the food we eat and regulate bowel function.

However, some people diagnosed with IBS have an increased number of bacteria in the small intestine (referred to as small intestinal bacterial overgrowth, or SIBO) and can experience an improvement in their symptoms with antibiotic treatment and removal of the bacterial overgrowth.

More needs to be learned about the possible role of bacteria with IBS. It is advisable to discuss this with a doctor.

Learn more about IBS and your gut

Adapted from IFFGD Publication #101 “IBS Brochure” By: Lin Chang MD, Professor of Medicine at the David Geffen School of Medicine at UCLA, Los Angeles, CA; adapted from article by Douglas A. Drossman MD, Drossman Gastroenterology PLLC, Chapel Hill, NC; edited by William D. Chey MD, Nostrant Collegiate Professor, University of Michigan, Ann Arbor, MI

Also adapted from IFFGD Publication #133 Gut-Brain Axis and IBS By: Christina H. Jagielski, Ph.D., M.P.H., GI Health Psychologist, GI Behavioral Health Program, Michigan Medicine; Edited by: Lin Chang, M.D., UCLA School of Medicine, Los Angeles

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IFFGD is a nonprofit education and research organization. Our mission is to inform, assist, and support people affected by gastrointestinal disorders.

Our original content is authored specifically for IFFGD readers, in response to your questions and concerns.

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