What Are the Causes of IBS?

Reviewed by: HU Medical Review Board | Last reviewed December 2022

Despite many advances in research in the last few decades, the cause of irritable bowel syndrome (IBS) is still not fully understood. Researchers have narrowed the likely causes of IBS to 3 key factors: gut physiology (how the gut works), environmental, and psychosocial factors.1-3

These factors may occur on their own or in combination. Continue reading to learn how they play a role in an IBS diagnosis.1-3

Gut physiology factors

Examples of gut physiology include:1-3

  • Genetics
  • Gut motility issues
  • Increased gut sensitivity
  • Gut inflammation
  • Changes to the gut microbiome


People with IBS are more likely to have family members with IBS. Experts are studying certain genes that may increase a person's risk of developing IBS. These genes may predispose someone to hypersensitivity, inflammation, and pain responses.1-3

Gut motility issues

Motility is a word used to describe the contraction of muscles in the gut that move, mix, and allow for food to be absorbed. Some people may have an exaggerated or abnormal response to gut-related hormones. This can change the way the muscles in the intestines contract.1,2

The time it takes for food to move through the colon may increase or decrease depending on the type of symptoms (constipation versus diarrhea).1

Increased gut sensitivity

There may be issues with how the brain and gut communicate (brain-gut axis). This may lead to increased sensitivity to pain signals. This is called visceral hypersensitivity.1-3

Gut inflammation

A person with IBS may have an abnormal balance of immune system cells along the GI tract. An increase in immune cells can produce inflammation and signals that lead to changes in gut function. This can cause IBS-related symptoms such as pain or diarrhea.1

Changes to the gut microbiome

When the gut’s microbiome – the trillions of bacteria that help keep our guts healthy – is out of balance, it can lead to IBS symptoms.1,3

Other factors that can throw the gut off balance and lead to IBS symptoms include:1-3

  • Difficulty absorbing nutrients (malabsorption)
  • Increases in hormone-producing or immune system cells
  • Antibiotics used to treat infections

Environmental factors

Examples of environmental factors are:1-3

  • Diet
  • Smoking
  • Gastrointestinal (GI) infections (bacterial, viral, parasitic)


A food intolerance or sensitivity, as well as malabsorption issues, can trigger IBS-related symptoms. Food intolerances are different from food allergies.1-3

It is unclear if these lead to IBS itself or if the condition shares symptoms with other disorders like celiac disease. But certain foods such as dairy, gluten, carbonated beverages, alcohol, caffeine, fatty foods, and gassy foods like broccoli, Brussels sprouts, and cauliflower are some of the worst offenders.1,3


Smoking can irritate the GI tract and trigger uncomfortable IBS symptoms. If you smoke, take steps to quit.4

GI infections

Severe GI infections caused by viruses, bacteria, or other germs – for example, traveler’s diarrhea – can cause inflammation and changes in the gut microbiome. Foreign bacteria in the gut may disrupt the normal environment of the intestine and lead to inflammation.1,3

This is called post-infectious IBS. After having a severe GI infection, a person is 6 times more likely to develop IBS.1

Psychosocial factors

The brain and gut are closely connected. When the brain is experiencing distress, the gut can as well. Examples of psychosocial factors include:1-3

  • Emotional or physical stress
  • Experience with or history of abuse
  • Anxiety or depression

Emotional or physical stress

Stress can trigger IBS symptoms. It can be helpful to learn healthy coping strategies, such as exercise and meditation, that can help alleviate stress in your life. While all stress will not go away, it can be reduced. Reducing stress can help lessen the severity of IBS symptoms.1-3

Experience with or history of abuse

Some studies show a connection between early life stress – such as abuse – and IBS. More research is needed to fully understand this possible correlation.1,3

Anxiety or depression

Anxiety and depression are 2 mood disorders that are closely linked with IBS symptoms. People who have anxiety or depression are at a greater risk of having IBS. And IBS symptoms can make anxiety and depression worse.1-3

If you live with anxiety, depression, or stress, talk to your doctor about getting the mental health support you need. Stress relief, counseling, and antidepressants are often part of the IBS treatment plan.5,6

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