The term inflammatory bowel disease (IBD) describes a group of disorders in which the intestines become inflamed. It has often been thought of as an autoimmune disease, but research suggests that the chronic inflammation may not be due to the immune system attacking the body itself. Instead, it is a result of the immune system attacking a harmless virus, bacteria, or food in the gut, causing inflammation that leads to bowel injury. Two major types of IBD are ulcerative colitis and Crohn's disease. Ulcerative colitis is limited to the colon or large intestine. Crohn's disease, on the other hand, can involve any part of the gastrointestinal tract from the mouth to the anus. Most commonly, though, it affects the last part of the small intestine or the colon or both. If you have an IBD, you know it usually runs a waxing and waning course. When there is severe inflammation, the disease is considered active and the person experiences a flare-up of symptoms. When there is less or no inflammation, the person usually is without symptoms and the disease is said to be in remission.
IBD is a disease with an unknown cause. Some agent or a combination of agents -- bacteria, viruses, antigens -- triggers the body's immune system to produce an inflammatory reaction in the intestinal tract. Recent studies show some combination of hereditary, genetic, and/or environmental factors may cause the development of IBD. It could also be that the body's own tissue causes an autoimmune response. Whatever causes it, the reaction continues without control and damages the intestinal wall, leading to diarrhea and abdominal pain.