The term inflammatory bowel disease (IBD) covers a group of disorders in which the intestines become inflamed (red and swollen), probably as a result of an immune reaction of the body against its own intestinal tissue.
Two major types of IBD are described: ulcerative colitis and Crohn's disease. As the name suggests, ulcerative colitis is limited to the colon (large intestine). Although Crohn's disease can involve any part of the gastrointestinal tract from the mouth to the anus, it most commonly affects the small intestine and/or the colon.
Both ulcerative colitis and Crohn's disease usually run a waxing and waning course in the intensity and severity of illness. When there is severe inflammation, the disease is considered to be in an active stage, and the person experiences a flare-up of the condition. When the degree of inflammation is less (or absent), the person usually is without symptoms, and the disease is considered to be in remission.