Digestive Disorders > IBD > Crohn's Disease

Crohn's disease causes: Searching for triggers

Dr. med. Andre Sommer

Dr. med. Andre Sommer

There are many theories about the causes of Crohn's disease. It can occur in genetically predisposed individuals who are repeatedly exposed to one or more environmental factors. The immune system then produces an excessive inflammatory response.

Below, we present important environmental factors and explain how science understands them as possible triggers for Crohn's disease. Not all factors are equally accepted and some are more demonstrable than others due to the quality and number of studies.

Is Crohn's disease a genetic disease?

Even if the exact cause of Crohn's disease is unknown, genetic factors seem to play a role at least. The likelihood of developing an inflammatory bowel disease such as Crohn's disease is:

  • 30 percent if both parents also have an inflammatory bowel disease.
  • 10 percent if one parent has inflammatory bowel disease.

Siblings have a 5 percent risk of getting Crohn’s. No single causative gene for Crohn's disease can be identified. Instead, several genes are involved. However, not all people with these genes develop Crohn's disease. Rather, the development of the disease is subject to an interaction of genes and environmental factors.

How do environmental factors change our immune system and trigger Crohn's?

Environmental factors come into contact with our defense system in various ways. They either directly affect our immune cells or damage body cells, which in turn attract inflammatory cells. The following is known about Crohn's disease:

  • Complex signaling pathways between intestinal cells and immune cells lead to an inflammatory reaction
  • The exact signal paths are only partially known
  • Inflammatory and anti-inflammatory proteins are out of balance and this seems to be more important than their number
  • Several proteins that control cell growth and differentiation are involved in the inflammatory process
  • A large number of breakdown products are created in the intestine, which contribute to tissue damage and cell death

Does smoking cause Crohn's disease?

Cigarette smoking is the best documented environmental risk factor in Crohn's disease. It not only increases the likelihood of developing the disease, but also worsens the prognosis. In the treatment of smokers, the medicinal effectiveness is also reduced. Researchers describe the reason for this as a change in the composition of the intestinal flora, new signaling pathways and cell damage in the intestinal wall.

Can bacteria and viruses trigger it?

Twin studies have shown that childhood gastrointestinal infections and mumps increase the risk of Crohn's disease. Other studies have shown that inflammatory bowel disease is common in areas where lakes, rivers, or drinking water have been contaminated. Scientific experts are discussing whether Crohn's disease is triggered, among other things, by pathogens that have been transmitted from animals to humans (e.g. via water). That would explain frequent occurrences in individual regions.

Do antibiotics and vaccinations trigger Crohn's disease?

A large Finnish study in children showed an association of Crohn's disease with antibiotics, especially for the group of cephalosporins and especially for boys. Unfortunately, further large studies on this are still missing. The use of cephalosporins was not reduced, since the occurrence of Crohn's disease is rather rare overall (7 new cases per 100,000 inhabitants annually) and cephalosporins can sometimes be life-saving.

Vaccinations do not increase the risk of Crohn's disease.

What drugs trigger Crohn's disease?

Crohn's disease is more common in people who have a history of taking nonsteroidal anti-inflammatory drugs such as ibuprofen. However, there is no association with aspirin. The results on hormone therapies as triggers are still controversial. However, an association between Crohn's disease and oral contraceptives has been demonstrated: A British twin study even showed a four-fold increased risk here. Postmenopausal estrogen therapy does not increase the risk of Crohn's disease.

Is the hygiene hypothesis correct?

According to the hygiene hypothesis, some people develop Crohn's disease because they were not exposed to sufficient bacteria and germs as children. According to this theory, the intestinal flora can be damaged if the baby is born with a Caesarean section, does not drink breast milk, or grows up in a household that is too clean. In the past, individual studies have described protective effects from breastfeeding or vaginal births, which could not be confirmed in recent large studies. Thus, the hygiene hypothesis remains controversial among scientists and is not considered an indicator of an increase in risk for Crohn's disease.

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Can physical activity prevent Crohn's disease?

Physical activity stimulates cell metabolism, which can also be useful in fighting inflammation. A large American study has even shown that exercise reduces the risk of Crohn's disease by 44% (women only). Interestingly, the risk did not decrease in men, nor in patients with ulcerative colitis, another inflammatory bowel disease. Scientists have not yet clarified why sport only has positive effects on women for Crohn's disease.

What influence does sleep have?

Generally, disturbed sleep is associated with poorer health. However, there are currently no comprehensive studies on sleep as a cause of Crohn's disease. It is known that patients with Crohn’s disease and sleep disturbances have fewer periods without symptoms. Therefore, patients should pay attention to their sleep and treating doctors should treat sleep disorders.

Is Crohn's disease associated with psychiatric disorders?

People with Crohn's disease have psychiatric disorders such as depression or anxiety more often than the general population. It has long been held that mental disorders, stressful life events or stress cannot be the cause of Crohn's disease. However, studies from recent years now suggest depression as a possible cause. It could lead to the release of stress hormones, which act throughout the body and thereby also release inflammation mediators in the intestine (stress axis). The mechanism is not yet understood, but it’s getting more and more attention among experts.

Does psychological stress affect the course of the disease?

Stress and illnesses with a changed mood (e.g. depression, mania, bipolar disorder) can negatively influence the course of the disease. When Crohn's inflammatory activity increases, the symptoms of a mental illness can also increase. For the treatment of Crohn's disease, contact should be made with a psychotherapist. Children and young people and their families in particular seek support.

Can the wrong diet trigger Crohn's disease?

Diet changes our intestinal flora, which makes a decisive contribution to the development of inflammatory bowel diseases. Several studies looked at the pre-onset eating habits of Crohn's disease patients and compared them to healthy people. More information about Crohn’s disease can be found here:

Healthy study participants eat:


  • Sugar
  • Meat
  • Fat


  • Vegetables
  • Dietary fiber
  • Vitamins

Daily fast food and high sugar consumption were associated with an earlier onset of illness in a study in children.

Does the sun protect against Crohn's disease?

Inflammatory bowel diseases are most common in Canada and Northern Europe. Scientists explain the north-south divide by our vitamin D production. The more exposed we are to the sun, the higher the vitamin D level in the blood, and at least in mouse models, insufficient vitamin D had an influence on the development of the disease. It is still unclear whether this also applies to humans.

Known risks or associated factors of Crohn's disease

  • Genetic disposition
  • Smoking
  • Infections (childhood gastrointestinal infections, mumps, contaminated water)
  • Antibiotics in boys (Cefalosporine)
  • Non-steroidal anti-inflammatory drugs such as ibuprofen
  • Oral contraceptives
  • Physical inactivity in women
  • Depression and fear
  • Unhealthy nutrition

Preiß, J. C., Bokemeyer, B., Buhr, H. J., Dignaß, A., Häuser, W., Hartmann, F., ... & Kucharzik, T. (2014). Aktualisierte S3-Leitlinie–„Diagnostik und Therapie des Morbus Crohn “2014. Zeitschrift für Gastroenterologie, 52(12), 1431-1484. Downloaded online on 30/06/2018 from https://www.kompetenznetz-darmerkrankungen.de/files/cto_layout/img/Diagnostik-und-Therapie-des-M.Crohn.pdf.

O’Toole, A., & Korzenik, J. (2014). Environmental triggers for IBD. Current gastroenterology reports, 16(7), 396. Downloaded on 30/06/2018 from https://link.springer.com/article/10.1007%2Fs11894-014-0396-y

Halme, L., Paavola-Sakki, P., Turunen, U., Lappalainen, M., Färkkilä, M., & Kontula, K. (2006). Family and twin studies in inflammatory bowel disease. World Journal of Gastroenterology: WJG, 12(23), 3668. Downloaded on 02/07/2018 https://www.wjgnet.com/1007-9327/full/v12/i23/3668.htm

Dr. med. Andre Sommer

Dr. med. Andre Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara.

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