What Is It?
Ulcerative colitis is an inflammatory disease. It usually begins in the rectum, then worsens to involve some or all of the large intestine. Ulcerative colitis is a lifelong condition.
Ulcerative colitis may begin with a breakdown in the lining of the intestine. The inside of the intestine, with its digested food, contains trillions of bacteria. Normally, the lining of the intestines keeps these bacteria from causing an infection of the wall of the intestine.
As long as the bacteria are contained, they remain invisible to your immune cells. They do not provoke a reaction. But when the intestine's lining fails, bacteria that usually are harmless can activate your immune system.