What causes Crohn’s disease?

The exact cause of Crohn's disease still isn't known, but certain risk factors have been identified:

• Immune system problems
• Genetics
• Environmental factors
• Smoking
• Infections

How do immune system problems relate to Crohn's disease?

Scientists have linked immune system problems to inflammatory bowel disease (IBD), including Crohn's. Usually, cells of the immune system defend the body from harmful microbes - bacteria, viruses, fungi, and other foreign substances - that have entered your body. Your body doesn't usually respond to all microbes, however. Many microbes are helpful, especially for digestion, and so the immune system leaves them alone.

If there is an invader that needs to be eliminated, your body's defence reaction begins. This immune system response causes inflammation. Immune system cells, chemicals, and fluids flood to the site to overcome the offending substance. After the substance has been disabled or removed, the immune response ends. Inflammation subsides.

For some reason, though, people with Crohn's disease have an immune system that reacts inappropriately. The immune system may be defending the body against helpful microbes by mistake. Or, for some other reason, the inflammatory response simply will not stop. Either way, in time, this chronic inflammation in the digestive system can result in ulcers and other injuries to the intestines.

Is genetics connected to Crohn's disease?

Brothers, sisters, children, and parents of persons with IBD, including Crohn's disease, are more likely to develop the disease themselves. About 10% to 20% of people with Crohn's disease have at least one other family member who also has the disease. And the disease is more common in certain ethnic groups, such as people of Jewish descent and Caucasians.

Is this tendency toward IBD and Crohn's disease passed genetically? Scientists have identified more than 200 different genes that are more common in those with Crohn’s disease than in those without the disease.

Do environmental factors play a role in Crohn's disease, too?

Environmental factors may help trigger Crohn's disease. These environmental factors may include any of the following:

• Substances from something you've eaten
• Microbes such as bacteria or viruses
• Cigarette smoke - smokers are twice as likely to develop Crohn’s disease than those who don’t smoke
• Other substances that are yet unknown

Environmental factors may contribute to Crohn's disease in one of these two ways:

• They may trigger an immune system response. Once started, the response cannot stop.
• They may directly damage the lining of the intestines. This may cause Crohn's disease to begin or to speed up.
• Previous infection. The bacterium Mycobacterium avium subspecies paratuberculosis (MAP) found in cows, sheep and goats may be a possible trigger.

What can I do to control Crohn's disease?

The factors involved in causing Crohn's disease are complex. Scientists continue to seek more information about the causes - in hopes of finding better ways to diagnose, treat, and perhaps even cure this frustrating and painful disease. In the meantime, understanding current theories about the causes of Crohn's disease can help you work with your doctor to explore how various treatments might work to control this condition.