Crohn's Disease: Causes and Risk Factors

Crohn’s disease is an idiopathic condition, which means that scientists aren’t yet sure exactly what causes the disease. However, the theories on what might cause Crohn’s disease and other forms of inflammatory bowel disease (IBD) are narrowing, and the current thinking is that it may be a complex interaction of several factors, including genes, immune system involvement, and environmental triggers.

Crohn's disease causes and risk factors
© Verywell, 2018


It's taking time to pin down the exact nature of how Crohn’s disease may be inherited because while it has been known for some time that it “runs in families,” it was not exactly clear how that occurred.

Scientists have now identified about 200 genes that may be involved in the development of Crohn’s disease.

Anywhere from 2 to 14 percent of people who have Crohn’s have a relative who also has the disease, meaning that most people who have IBD actually do not have a relative that also has the condition.

However, for people who have a family member who has IBD, the risk of developing the disease is increased. It's thought that having the genes alone isn't enough to develop Crohn's disease and that there must also be one or more "triggers" that lead to the development of IBD. Because not everyone who carries the genes associated with Crohn’s disease eventually develops the condition, it’s understood that the cause includes more than the hereditary factor.

Autoimmune Reaction

Crohn’s disease is often described as an autoimmune condition, or, more recently, an immune-mediated condition. This is because the disease is thought in part to stem from a problem in the immune system.

For some reason that is still unclear to scientists, the immune system may be triggered to "attack" healthy parts of the digestive system. This is why Crohn’s disease is often treated with medications that suppress the immune system. When the immune system is tamped down, it can decrease the effects that the overactivity is having on the digestive system.

The misfire in the immune system may come from a type of allergic response that causes the release of an abundance of eosinophils. Eosinophils are cells that fight off the allergic response. In doing so, they release compounds that are toxic. Research shows a relationship between people with Crohn’s disease and an excess amount of eosinophils in their blood and tissues.

Environmental Triggers

Even after the genetic and immune system factors are taken into account, there still may be more to the development of Crohn’s disease.

Scientists also think there may be one or more environmental triggers that are involved with Crohn’s disease.

It’s currently unknown how many of these triggers there are or how they may interact with the other potential causes of Crohn’s disease. A few possible triggers that are under study include:

  • Smoking. Cigarettes worsen Crohn’s disease and people with the disease are encouraged not to smoke. People who currently smoke or who have smoked in the past have an increased risk of developing Crohn’s disease.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs). These common painkillers may be associated with precipitating or worsening Crohn’s disease flare-ups. It’s unclear the role (if any) that they may play in the development of the disease.
  • Antibiotics. There is some evidence that the use of antibiotics, especially early in life, could contribute to the development of Crohn’s disease. In some people, antibiotics are also associated with flare-ups of the disease.
  • Contraceptive pill. There is some evidence that the contraceptive pill (birth control pill) may be associated with a small increase in the risk of developing Crohn’s disease.
  • Geographic location. Crohn’s disease is more common in the industrialized world, particularly in North America and Western Europe, though the incidence is rising in Asia and South America.

Debunking Common Myths

Researchers don’t know exactly why people develop Crohn’s disease, which has led to many incorrect ideas and dead ends about the factors that can cause the disease.

We now know that diet and stress, which were thought to play major roles in the development of Crohn’s disease, actually do not cause IBD. Stress reduction and dietary modifications can be a part of treatment, but these lifestyle factors are neither causes or cures for IBD.

Frequently Asked Questions

  • Can ethnicity or race be a risk factor for Crohn's disease?

    Crohn's can affect people of all ethnicities. However, it is more common in those with eastern European backgrounds, and the rate is increasing for Black people in the United States.

  • What causes Crohn's disease flare-ups?

    Some factors that can cause symptoms to flare up include missing an IBD medication, taking antibiotics, smoking, and feeling stressed. Talk with your healthcare provider about what causes your flares and how to manage symptoms.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Shi HY, Ng SC. The state of the art on treatment of Crohn's disease. J Gastroenterol. 2018;53(9):989-998. doi:10.1007/s00535-018-1479-6

  2. U.S. National Library of Medicine. Genetics Home Reference. Crohn disease

  3. Katsanos KH, Zinovieva E, Lambri E, Tsianos EV. Eosinophilic-Crohn overlap colitis and review of the literature. J Crohns Colitis. 2011;5(3):256-61. doi:10.1016/j.crohns.2011.02.009

  4. Feuerstein JD, Cheifetz AS. Crohn Disease: Epidemiology, Diagnosis, and Management. Mayo Clin Proc. 2017;92(7):1088-1103. doi:10.1016/j.mayocp.2017.04.010

  5. Crohn’s & Colitis Foundation. Causes of Crohn’s Disease

  6. Crohn's & Colitis Foundation. Causes of Crohn's disease.

  7. Crohn's & Colitis Foundation. Managing flares and IBD symptoms.

Additional Reading
  • Halme L., Paavola-Sakki P., Turunen U., Lappalainen M., Farkkila M., Kontula K. "Family and twin studies in inflammatory bowel disease." World J Gastroenterol. 2006;12:3668–3672.
  • Liu JZ, Anderson CA. "Genetic studies of Crohn’s disease: Past, present and future." Best Practice & Research Clinical Gastroenterology. 2014;28:373-386. doi: :10.1016/j.bpg.2014.04.009.
  • Zhou M, He J, Shen Y, Zhang C, Wang J, Chen Y. "New Frontiers in Genetics, Gut Microbiota, and Immunity: A Rosetta Stone for the Pathogenesis of Inflammatory Bowel Disease." BioMed Research International. 2017;2017:8201672. doi: :10.1155/2017/8201672.

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.