Health A-Z

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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.

Ulcerative colitis is an autoimmune disease. This means that the immune system, which is supposed to attack foreign things that get inside our bodies, instead attacks a part of the body.

In ulcerative colitis, the bowel bacteria provoke the immune system to attack the wall of the intestine itself, injuring the bowel.

Once the bowel inflammation has started, it can continue. It continues even if the immune system stops being exposed to the bowel bacteria.

Ulcerative colitis affects the inner lining of the rectum and colon. This causes the lining to:

  • Wear away in spots (leaving ulcers)

  • Bleed

  • Ooze cloudy mucus or pus

Sometimes, other parts of the body are affected by the inflammation. These include the eyes, skin, liver, back and joints.

The disease is not contagious. Contact with another person cannot spread the disease.

Ulcerative colitis usually begins to cause symptoms between the ages of 15 and 40.

Ulcerative colitis substantially increases the risk of colon cancer.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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