Crohn's disease is an inflammatory bowel disease (IBD). It is a chronic condition that may recur at various times over a lifetime. It usually involves the small intestine, most often the lower part called the ileum. In some cases, both the small and large intestine are affected. Inflammation may also affect the entire digestive tract, including the mouth, esophagus, stomach, duodenum, appendix or anus.
Ulcerative colitis is an inflammatory bowel disease (IBD) in which the inner lining of the large intestine (colon or bowel) and rectum become inflamed. Inflammation usually begins in the rectum and lower (sigmoid) intestine and spreads upward to the entire colon. Ulcerative colitis rarely affects the small intestine, except for the lower section, the ileum.