Is Crohn’s Disease Contagious?

Crohn’s disease is a type of inflammatory bowel disease (IBD) in which parts of the digestive tract are inflamed. The most common area that is affected by Crohn's is the lower part of the ileum, the longest part of the small intestine. It's also often found in the colon, the longest part of the large intestine. Over time, the inflammation can lead to scarring and complications.

The predominant symptom of Crohn's is diarrhea, but people may also have crampy abdominal pain and weight loss. Although it is a digestive disease, Crohn's can affect your health in other ways, as well. You may feel tired, have eye redness or pain, become anemic (lacking healthy red blood cells to carry oxygen throughout the body), and have joint pain and soreness.

If someone you love has Crohn's, you might wonder if you can "catch" it from them. Rest assured that even though it's not clear why some people get the disease and others don't, there is no evidence that Crohn's is contagious.

Here's what the science says about the key factors that may increase your risk of developing Crohn's disease.

How Do People Get Crohn's?

The cause of Crohn’s disease is not known, but there are several risk factors that are associated with the disease, including genetics, excessive use of anti-inflammatory drugs, such as aspirin or Advil or Motrin (ibuprofen), and eating a high-fat diet. Autoimmunity, which is when the immune system attacks healthy cells because it mistakenly perceives them as being a threat, may also play a role in the development of the disease.

Genetics

Research has found several genetic markers that may indicate which people are genetically predisposed to developing Crohn's. Specific genes associated with the disease include:

• NOD2: The gene that provides instructions for making a protein that plays an important role in immune system function
• IL23R: The gene that provides instructions for making a protein called the interleukin 23 (IL-23) receptor, an immune system molecule that is active in Crohn's disease
• ATG16L1: The gene that provides instructions to create a protein that is used to clean out damaged cells from the body

Heredity

Crohn’s disease seems to run in families and up to 20% of people with a first-degree relative (such as a parent) will also develop inflammatory bowel disease (IBD). The risk increases significantly if a person has two parents with IBD or is of Eastern European descent. African American populations have also reported higher numbers of Crohn’s disease in recent years.

Environment

There are several known environmental factors that appear to contribute to a person's risk of developing Crohn's disease in their lifetime.

For example, people who live in developed countries and cities are far more likely to have Crohn’s than those who live in rural or underdeveloped areas and countries. Living in a northern climate also appears to be a factor.

The MAP Theory

Another idea is the MAP theory, which is based on a specific bacterium known as the Mycobacterium avium subspecies paratuberculosis (MAP). The bacterium typically causes chronic digestive disease in animals such as nonhuman primates and dairy cows.

Research has shown that many people with Crohn’s have this bacterium in their bodies. However, simply becoming infected with this type of bacteria will not lead to Crohn’s. There are also other factors that contribute, including:

• The age at infection: Children would need a smaller amount of MAP to become infected enough to develop Crohn’s.
• Sex: Adult females are more likely to develop Crohn’s following a MAP infection, whereas infant males are more likely to develop the disease after getting the infection.
• Genetics: People who have certain genes may develop Crohn’s after a MAP infection because of the way that their genes process the bacterium in the body.
• How much bacteria made their way into the body: Crohn's can develop if a lot of MAP bacterial organisms are found in the body.
• How the bacterium enters the body: MAP is thought to be transmitted through contaminated water or cow products, such as milk or beef. 

According to the MAP theory, both Crohn’s disease and ulcerative colitis—another inflammatory bowel disease—are caused by this bacterial infection. It is also believed that the reason why Crohn’s disease exists in families is that the MAP infection can be passed between close family members, such as from a parent to a child.

The MAP theory also suggests that as more countries become westernized, they are more likely to become infected with MAP from dairy products and beef.

Other Risk Factors

There are other risk factors that play a role in the development of Crohn’s, many of which have to do with other health conditions that a person might have, the medications that they may take, and certain aspects of their lifestyles.

Other potential risk factors for Crohn's are:

• Smoking: Smokers are more likely to have Crohn’s disease than nonsmokers.
• Appendectomy: Surgery to remove the appendix increases a person's risk for developing bowel disease.
• Medications: Some medications may irritate the bowel and lead to Crohn’s, such as anti-inflammatory drugs, birth control pills, and antibiotics.
• Nutrition: A high-fat diet may increase the risk of developing the disease.
• Stress: High levels of stress may activate inflammation in the digestive tract that can lead to the onset of Crohn’s.

Summary

If someone that you love has Crohn's, know that even though researchers are not sure why some people develop the condition and others do not, there is no evidence that it can be spread from person to person through close contact.

There are several known risk factors, including environmental exposures, some medications, other health conditions, and genetics, that all play a role in a person's risk of getting Crohn's.

A Word From Verywell

There are certain risk factors for Crohn's that you cannot control, such as your genes. However, you might be able to reduce your risk by making some changes in your life, such as quitting smoking or keeping your stress levels in check.

If you do not know whether you're at an increased risk for Crohn's disease or if you are not sure how you can lower your risk, share your concerns with your healthcare provider.