Colitis is an inflammatory bowel disease (IBD) affecting the large intestine or colon. Normally the body’s immune system fights protects from infection. In people affected with IBD, however, the immune system mistakes food, good bacteria and other intestinal items for foreign material and mounts an attack, sending white blood cells into the intestinal lining. The result is chronic inflammation and ulceration. Patients can experience persistent diarrhea or constipation, looser and more urgent bowel movements, abdominal pain and rectal bleeding. The symptoms come and go, with remission periods lasting anywhere from months to years.