What is Crohn's disease?

Crohn's disease is an inflammatory bowel disease that causes chronic inflammation and ulceration within the digestive tract. Ulcers in the intestinal lining and inflamed tissue may swell, redden and bleed, often leading to bloody diarrhea, abdominal pain and cramping. This irritation can run deep -- into all layers of your gastrointestinal lining. Inflammation may be confined to one location or it may occur in patches, with normal tissue located between inflamed areas.

How common is Crohn's disease?

About 500,000 Americans have Crohn's disease, according to the Crohn's & Colitis Foundation of America. Another 500,000 have ulcerative colitis, the other major type of inflammatory bowel disease. Crohn's disease most often occurs in young people between the ages of 15 and 35, but may also occur in older or younger populations.

What causes it?

The cause of Crohn's disease is unknown, but it appears to involve dysfunction of the immune system. Protective cells normally present in the gastrointestinal lining are triggered to attack when bacteria and viruses pass through the digestive tract. In people with Crohn's disease, this attack continues, even when harmful substances are no longer present, leading to chronic inflammation and irritation. It is not clear whether this immune dysfunction is a cause or result of Crohn's disease.

How does Crohn's disease affect people?