The cause of inflammatory bowel disease (IBD) is unknown. Since IBD appears to run in families, genetics and heredity may play a role. In fact, researchers resently linked the mutation of a specific gene to the development of Crohn’s disease (CD), a form of IBD. Another potential cause of IBD is the immune system. Patients with IBD experience an overreaction of their immune system. Once it is triggered to fight harmful substances, it appears unable to turn off. It continues to attack normal intestinal cells, leading to chronic inflammation and irritation. The cause of this problem is unknown, although infection, injury, dietary choices or environmental triggers may play a role.

Men and women appear to be at equal risk of developing IBD. However, there are a number of known risk factors, including:

• Family history. Although estimates vary, somewhere between 10 to 30 percent of patients with IBD have a relative with the disease.
  
  
• Age. Young people are more likely to develop IBD than older patients. Most often, IBD first appears between the ages of 10 to 35.
  
  
• Race and ethnicity. Whites have a higher risk of developing IBD than non-whites. The risk of IBD is greater for people with a Jewish ethnic background, especially those of European descent, than other ethnic groups. IBD is a disease of the developed world, occurring primarily in the United States and Europe.

Cigarette smoking appears to have an effect on patients with IBD. The reason for this is not fully understood. However, IBD patients who smoke are more likely to have a more aggressive form of IBD than non-smokers. In addition, smokers are more likely to develop Crohn's disease than non-smokers. However, for ulcerative colitis (UC), the opposite is true – non-smokers are more likely to develop UC than smokers.