CROHN'S DISEASE and ULCERATIVE COLITIS are chronic inflammatory diseases characterised by relapsing and remitting episodes over many years. The diseases are similar and are both classified as IBD, but a significant distinction is that Crohn's disease can affect any part of the GASTROINTESTINAL TRACT from mouth to anus, whereas ulcerative colitis affects only the COLON. The incidence of IBD varies widely between countries, being rare in the developing world but much more common in Westernised nations, where the incidence of Crohn's disease is around 5–7 per 100,000 (and rising) and that of ulcerative colitis at a broadly stable 10 per 100,000. It is common for both disorders to develop in young adults, but there is a second spike of incidence in people in their 70s. Details about the two disorders are given under the individual entries elsewhere in the dictionary. Inflammatory bowel disease should not be confused with IRRITABLE BOWEL SYNDROME (IBS) which has some of the same symptoms of IBD but a different cause and outcome.