Causes:
One possible cause is an immune system malfunction. When your immune system tries to fight off an invading virus or bacterium, an abnormal immune response causes the immune system to attack the cells in the digestive tract, too. Heredity also seems to play a role in that IBD is more common in people who have family members with the disease. However, most people with IBD don't have this family history.
Risk factors:
• Age: Most people who develop IBD are diagnosed before they're 30 years old. But some people don't develop the disease until their 50s or 60s.
• Race or ethnicity: Although whites have the highest risk of the disease, it can occur in any race.
• Family history: You're at higher risk if you have a close relative — such as a parent, sibling or child — with the disease.
• Cigarette smoking: Cigarette smoking is the most important controllable risk factor for developing Crohn's disease.
Courtesy: Mayo Clinic