Colitis is an inflammation of the colon, also known as the large intestine. While there are many causes of colitis including infections, poor blood supply (ischemia), and autoimmune reactions, they share common symptoms of abdominal pain and diarrhea. Ulcerative colitis is an inflammatory bowel disease (IBD) that causes long-lasting inflammation and ulcers (sores) in your digestive tract. Ulcerative colitis affects the innermost lining of your large intestine (colon) and rectum. Symptoms usually develop over time, rather than suddenly. Ulcerative colitis can be debilitating and can sometimes lead to life-threatening complications.