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?

People with Crohn's disease have a wide variety of symptoms. This is because the disease can affect different parts of the digestive tract and in different ways, such as with swelling, edema or the development of abnormal passages called fistulae. Crohn's disease can cause deep tissue irritation and can lead to serious medical complications, such as obstruction or perforation of the intestines, which can require surgery. People with Crohn's disease may experience alternating periods of symptom activity and relief throughout their lives.