Causes and Risk Factors of Inflammatory Bowel Disease

There are several theories about what causes inflammatory bowel disease (IBD), but none are confirmed. As an idiopathic disease, or one of unknown cause, it may be that one or several factors give rise to the diseases that comprise IBD (ulcerative colitisCrohn's disease, and indeterminate colitis). A malfunctioning immune system, genetics, other conditions, and certain risk factors may all potentially play a role.

While it was once thought that what you eat and your stress levels could cause IBD, that is no longer the case. (Though they can induce an IBD flare in those who have the condition.)

Common Causes

IBD is frequently called autoimmune disease, a disease that is triggered by the immune system, but it is more accurate to say that it is an immune-mediated response. Seasonal flare-ups—during the spring or autumn—sometimes occur in people with IBD.

Allergic Response

One theory is that IBD is an IgE-mediated allergic response. The allergic response sets off a chain of events resulting in an excess of eosinophils (cells that try to fight the allergic response) in the body.

These eosinophils release four toxic compounds, three of which are found in statistically significant amounts in the stool of IBD patients (via a fecal calprotectin test). This leads some researchers to conclude that an allergic response may have a role in the development of IBD.


Another strong area of research is the role that cytokines play in the development of IBD. Cells called tumor necrosis factor (TNF, tumor necrosis factor-alpha) are responsible for regulating the immune response, among other functions.

Here too, TNF is found in higher quantities in the stool of people with IBD than it is in people who do not have IBD.

Several anti-TNF drugs (commonly called biologics) have been developed to treat IBD. The success of these medications lends some weight to the idea that TNF plays some role in causing IBD or the inflammation associated with IBD flare-ups.


Years ago, it was thought that IBD might run in families, but the link seemed tenuous because it was not a direct parent-to-child situation, as is the case with some inherited conditions.

But with the discovery of hundreds of genes that may be associated with IBD, it has become apparent that there is a hereditary component to it. First-degree relatives of people who have IBD are significantly more likely to also have the disease.

Some research points at a few possibilities for the reason some people who have IBD genes develop IBD and other people do not. Still, the majority of people who have IBD have no family history.

While researchers have learned a lot about the genes that may be associated with IBD, it's the trigger part that is difficult to pin down. It's now also thought that there could be hundreds of different types of IBD. There could, in fact, also be hundreds or thousands of triggers.

Lifestyle Factors

Given that some people with the same genes develop IBD, while others do not, something other than genetics needs to be taken into consideration when looking at the possible causes of IBD.

There are some clear trends in the epidemiology of IBD that may point to one or more environmental causes. IBD tends to occur most often in developed countries and amongst those with higher socioeconomic status. IBD also tends to occur more often in the urban areas of developed countries.

These factors have led researchers to think that there may be some connection between IBD and the lifestyles or environment of people living in developed countries, although no one knows yet what this could be.

One suggested theory is that industrialized nations are "too clean", and because children and adolescents are exposed to fewer bacteria, their immune systems may be inadequate, which leads to autoimmune disease.

A Word From Verywell

While the exact cause of IBD is not clear, experts know so much more about the disease now than just a decade ago. More research is being done, and scientists are getting closer and closer to understanding how doctors can treat IBD more effectively and prevent it in future generations.

Frequently Asked Questions

  • What does IBD pain feel like when it flares up?

    IBD pain can depend on the specific condition. For example, pain that feels like cramps in the middle or upper part of the abdomen is likely caused by Crohn's disease, whereas pain on the left side of the abdomen (sometimes severe) is a typical symptom of ulcerative colitis.

  • How does blood appear in the stool of people with IBD?

    Blood in the stool is more often a symptom of ulcerative colitis than Crohn's disease. It is caused by ulcers that line the intestine or rectum. If someone has Crohn's disease and sees blood in the stool, it is usually caused by inflammation in the colon or rectum.

9 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.
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  4. Zhang YZ, Li YY. Inflammatory bowel disease: pathogenesisWorld J Gastroenterol. 2014;20(1):91–99. doi:10.3748/wjg.v20.i1.91

  5. Crohn's and Colitis Foundation of America. About the epidemiology of IBD.

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

  7. Crohn's & Colitis Foundation. Types of ulcerative colitis.

  8. Ungaro R, Mehandru S, Allen PB, Peyrin-Biroulet L, Colombel JF. Ulcerative colitisLancet. 2017;389(10080):1756-1770. doi:10.1016/S0140-6736(16)32126-2

  9. Gajendran M, Loganathan P, Catinella AP, Hashash JG. A comprehensive review and update on Crohn's diseaseDis Mon. 2018;64(2):20-57. doi:10.1016/j.disamonth.2017.07.001

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.