An inflammatory bowel disease (IBD), Crohn's disease is a chronic condition that may recur at various times over a lifetime. Although Crohn’s disease may cause inflammation in any area of the gastrointestinal tract, it most commonly affects the small intestine — most often, the lower part called the ileum — and colon. In some cases, both the small and large intestine are affected. Sometimes, inflammation may affect the entire digestive tract, including the mouth, esophagus, stomach, duodenum, appendix and anus.
There are two types of inflammatory bowel diseases that affect the intestines: Crohn’s disease and ulcerative colitis (UC). The symptoms of these two illnesses are very similar, which often makes it difficult to distinguish between the two.
Unlike ulcerative colitis, which only affects the superficial, or outermost, tissue layers (called mucosa) of the colon, Crohn's disease can affect any layer of tissue in the gastrointestinal tract. Crohn's disease often spreads deep into the layers of affected tissues. Also, unlike ulcerative colitis, the inflammation is not consistent throughout the bowel. There may be healthy bowel tissue/mucosa in between areas of diseased bowel.
Although Crohn's disease can develop at any age, it is most commonly diagnosed in people 20 to 30 years old. Crohn's disease generally affects men and women equally. The disorder can affect any ethnic group. However, people of Jewish heritage are most likely to develop Crohn's disease, while African-Americans are less likely to develop it. In addition, it appears to run in some families, with about 20 percent of people with Crohn's disease having a blood relative with some form of IBD.
There are many theories regarding what causes Crohn's disease. One theory suggests that some agent, perhaps a virus or a bacterium, affects the body's immune system and triggers an inflammatory reaction in the intestinal wall. Although there is a lot of evidence that patients with this disease have abnormalities of the immune system, it is not known whether the immune problems are a cause or a result of the disease. There is no evidence that Crohn's disease is caused by stress.