Crohn's disease is a severe, chronic inflammatory bowel disease. It causes inflammation, ulcers, and bleeding in the digestive tract. It usually affects the end portion of the small intestine called the ileum. However, any part of the digestive tract can be affected, from the mouth to the anus.

Small Intestine
nucleus factsheet image
Copyright © Nucleus Medical Media, Inc.

The cause of Crohn's disease is not known. Inflammatory bowel diseases, such asulcerative colitis and Crohn's disease, seem to run in some families. Some researchers think that it is due to a reaction to a virus or bacteria. The immune system overreacts and causes damage to the intestines.