colitis, inflammation of the colon, or large intestine. The term "colitis" may be used to refer to any of a number of disorders involving the colon. Symptoms include diarrhea (often with blood and mucus), abdominal pain, and fever.

Ulcerative colitis is a serious chronic inflammation and ulceration of the lining of the colon and rectum. Another form of colitis, called Crohn's disease, has similar signs and includes thickening of the intestinal wall. The disease typically occurs in the small intestine near the point where it joins the colon, but the colon and other parts of the gastrointestinal tract may be affected as well. The term "inflammatory bowel disease" has been used to refer to both ulcerative colitis and Crohn's disease, the causes of which are unknown. A less severe disorder, known as irritable bowel syndrome, or IBS, was formerly called mucous colitis.

Colitis is sometimes caused by infections with viruses, parasites, or bacteria. For example, two distinct types of dysentery are caused by amebas and bacteria. Infectious forms of colitis are often the result of poor hygienic practices. Prolonged use of antibiotics can also cause colitis, either by direct irritation of the colon or by killing bacteria that normally live in the intestine, allowing the toxin-producing bacterium Clostridium difficile to proliferate. Colitis is also sometimes caused by diverticulitis (see under diverticulosis) or by colon cancer.

Inflammation of the colon, especially of its mucous membranes. The inflamed membranes develop patches of tiny ulcers, and the diarrhea contains blood and mucus. It often becomes chronic, with sustained fever and weight loss; complications and death may result. Specific causes, such as amoebic or bacillary dysentery, are rarer than unknown or multiple causes. If treatment with sulfasalazine, corticosteroids, immunosuppressive drugs, or antibiotics does not control it, part or all of the colon may have to be removed.

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