IBS-D is a complicated condition with several factors that can affect the digestive system. However, the precise cause of IBS-D is unknown. An imbalance in the normal healthy bacteria in the digestive system has been found in people with IBS-D. The bacteria and microorganisms in your digestives system, collectively called the microbiota, help you digest and absorb food and are constantly working to keep your body functioning normally.

Other factors could include improper signaling between the brain and the digestive system, inflammation or severe infection in the intestines, too strong or weak intestinal muscle contractions, family history and genetics, and in some cases anxiety and/or depression.