First of all, Crohn's disease is an inflammation that extends into the deeper layers of the intestinal wall. It is found most often in the ileum and the first part of the large intestine (cecum), known as the ileocecal region. The disorder, however, can develop in any part of the gastrointestinal tract, including the anus, stomach, esophagus, and even the mouth. It may affect the entire colon, or form a string of contiguous ulcers in one part of the colon, or develop as multiple scattered clusters of ulcers.

Although the causes of Crohn's Disease and IBD(Inflammatory Bowel Disease) in general are not yet known, genetic factors play some role. Up to 25% of people with IBD also have family members with the disease. The inherited risk is highest if a mother has the condition, followed by a sibling. A father with IBD poses the least inherited risk to his children. Although different genes play weaker or stronger roles in ulcerative colitis and Crohn's disease, a recent study reported that genetic abnormalities of the two disorders may share locations on chromosomes 1, 3, 4, 7, 12, and 16.

Some researchers believe that the disease develops in people who have a genetic susceptibility that enables an agent such as a virus or bacteria to trigger an abnormal immune response. If such organisms or other factors injure the lining of a healthy intestine, the immune system reduces inflammation and injury with white blood cells called suppressor T cells. In IBD, however, there appears to be an increase in white blood cells called helper-T cells, which produce damaging proteins known as cytokines. These proteins, particularly a powerful one called tumor necrosis factor, cause intestinal inflammation and damage, which, in a vicious cycle, attract even more helper-T cells. A protein on the surface of intestinal cells called ICAM-1 also plays a role. White blood cells are activated by increased levels of ICAM-1, which occur in IBD.

Different bacteria may be responsible for either Crohn's disease or ulcerative colitis. Studies have found that children with IBD are likely to have more and earlier childhood infections than children without the disorder. Viral infections during pregnancy may also increase the child's later risk for IBD. One study indicates that exposure to measles during pregnancy puts the baby at risk for developing Crohn's disease, although not ulcerative colitis. While a link between IBD and vaccination for measles, mumps, and rubella has been suggested a recent study has strongly refuted this association. Another suspect for Crohn's disease is a tuberculosis-like organism.

Because inflammatory bowel disease is much more prevalent in industrialized nations, experts believe environmental factors, such as diet, must play some role, although studies have been conflicting. One study found that high fat intake -- particularly animal fat -- was associated with later development of ulcerative colitis. A high sugar intake (from non-fruit sources) was related to both inflammatory bowel disorders. A high intake of fluids and diets rich in fruits, vitamin C, and magnesium were associated with a lower risk for both disorders, and a high intake of potassium and vegetables was associated with a lower risk for Crohn's only.

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