What Causes IBS?

Medically reviewed by Kumkum S. Patel MD, MPH

The exact cause of irritable bowel syndrome (IBS) is unknown. Sometimes, it develops after a severe bout of infectious diarrhea or trauma, but most cases have no specific cause. Some of the first signs of IBS include abdominal pain, bloating, diarrhea, and/or constipation.

Researchers think the causes may lie in how the gut and brain communicate. But there are other possibilities.

This article covers everything you need to know about common causes of IBS, triggers of IBS symptoms, and risk factors for developing IBS.

<p>Alexandar Georgiev / Getty Images</p>

Alexandar Georgiev / Getty Images

Common Causes of IBS

Experts aren’t sure of the exact cause of IBS, but these factors seem to play a role.

Early Life Stress or Psychological Trauma

Difficult or stressful early life events, such as physical or sexual abuse, may play a role in causing IBS. Some studies of animals have shown that early life trauma and stress can induce IBS into adulthood.

Research shows that adverse early life events significantly influence the communication pathways within the brain and the gut. However, the reasons for this are still poorly understood.

Changes in Gut Microbes

An altered gut microbiome (the mix of microorganisms such as bacteria, viruses, and fungi that live in the gastrointestinal tract) is often seen in people with IBS. This abnormal balance of microbes is often referred to as gut bacterial dysbiosis and is now being investigated as a possible cause of IBS.

Alterations in the gut microbiome can lead to inflammatory and immunologic changes that impair the gastrointestinal (GI) mucosal barrier by increasing gut permeability (the control of compounds passing from inside the GI tract through the gut wall into the rest of the body).

This, in turn, may interfere with the brain-gut axis, which is the bidirectional communication between the brain and the gut. The brain-gut axis plays an important role in the regulation of gut function.

Nervous System Issues

The brain and gut use the nervous system to send messages back and forth to each other (this is the brain-gut axis). Researchers are finding evidence that malfunctions along these nervous system pathways may contribute to symptoms of IBS, such as abdominal pain, diarrhea, and/or constipation.

Impairment of communication between the brain and gut disrupts the body’s ability to stay in homeostasis, a state in which all body systems are stable and able to adjust to changing external conditions.

These errors in gut-brain communication may be due to inflammation and oxidative stress in the gut. Oxidative stress occurs when antioxidants in cells can't keep up with neutralizing harmful compounds (free radicals) produced by processes in the body.

Experts suggest that inflammation leads to malfunctions in the nervous system response. This can affect GI motility (the movement of food through the GI tract) and sensitivity and may be involved in functional GI disorders, including IBS.

Muscle Contractions in the Intestine

IBS has sometimes been called “spastic colon” due to alterations seen in gut motility in people with IBS. The “spasms” are spontaneous contractions of the muscles of the intestines.

Increased or decreased frequency of contractions after eating may contribute to symptoms such as abdominal pain, cramping, bloating, diarrhea, and/or constipation.

The reasons for these increased muscle contractions may be due to other underlying causes of IBS, such as disruptions in the brain-gut axis, altered gut bacteria, visceral (referring to internal organs) hypersensitivity, stress, and inflammation.

Severe Infection

Severe bacterial infections in the digestive tract, such as viral or bacterial gastroenteritis, may be a cause for the development of IBS. This is called post-infectious IBS (PI-IBS).

Experts suggest that PI-IBS may develop in 10% of people with infectious gastroenteritis despite disease resolution. This may be due to persistent low-grade inflammation, changes in intestinal permeability (the ability of a substance to pass through the intestinal lining), increased visceral sensitivity, and alterations in the gut microbiome.

Repeated or Long-Term Antibiotic Use

Antibiotics are known the disrupt the bacteria in the gut. These changes can include reducing species diversity, altering metabolic activity, and increasing the amount of antibiotic-resistant organisms.

Increased, repeated, and long-term use of antibiotics only amplifies these negative effects on the gut microbiome. Over time, this may lead to increased gastrointestinal disturbances, including symptoms of IBS, such as abdominal pain and changes in bowel patterns.

Other Possible IBS Causes

As more research is conducted on potential causes of IBS, additional possible explanations have been suggested. These include having:

What Triggers IBS Symptoms?

Food is one of the most common triggers for IBS symptoms. Visceral hypersensitivity, gut motility, and gut bacterial dysbiosis seem to play a role in triggering symptoms after eating certain foods.

For example, some types of carbohydrates are quickly fermented in the large intestine but poorly absorbed. This leads to symptoms such as abdominal pain, bloating, distension, and gas.

Stress is another common trigger for IBS symptoms. Stress increases levels of the hormone cortisol, which is linked to a worsening of IBS symptoms.

As IBS is a disorder of the gut-brain axis, it seems plausible that stress (and thus cortisol) can affect this two-way communication. Chronic stress has been shown to change visceral sensitivity to pain, as well as alter gut motility and permeability.

What Foods May Cause IBS Triggers?

Many different foods can cause symptoms in people with IBS. Specific food triggers will vary from person to person and can change over time. Nevertheless, there are some common food triggers for people with IBS, such as:

  • Garlic

  • Onion

  • Wheat and rye

  • Cow’s milk and yogurt

  • Apples, pears, and cherries

  • Artichokes, leeks, mushrooms, and cauliflower

  • Legumes and pulses, such as kidney beans and split peas

  • Cashews and pistachios

  • Sweeteners, such as honey and high-fructose corn syrup

  • Sugar alcohols, such as sorbitol, xylitol, and erythritol

IBS Risk Factors

Though the exact cause of IBS is complex and still unknown, experts have found some common characteristics in those who have developed IBS. These include:

  • Age: Most people with IBS are younger than 50 years old.

  • Sex: Women have a higher prevalence of IBS than men.

  • Family history: People with a biological relative with IBS have double the risk of developing IBS.

  • Mental health issues: IBS is seen more in people with anxiety, depression, and somatic symptom disorder.

Lifestyle Risk Factors

In addition to the above risk factors, certain lifestyle habits may also increase the risk of developing IBS, such as:


Irritable bowel syndrome (IBS) is a multifaceted condition for which the exact cause is unknown. Possible causes include early-life stress or psychological trauma, changes in the gut microbiome, nervous system issues, alterations in gut motility and permeability, severe gastrointestinal infection, and long-term or repeated antibiotic use.

Other potential causes include small intestinal bacterial overgrowth (SIBO), increased gut sensitivity, food sensitivities or intolerances, and certain mental health issues.

Common triggers for IBS symptoms include certain foods and stress. Risk factors for developing IBS include being younger than 50 years old, being female, having a family history of IBS, and having certain mental health conditions.

Certain lifestyle factors may also increase your risk of IBS, such as smoking, excessive alcohol intake, chronic stress, lack of physical activity, and irregular eating habits.

A Note on Gender and Sex Terminology

Verywell Health acknowledges that sex and gender are related concepts, but they are not the same. To reflect our sources accurately, this article uses terms like “female,” “male,” “woman,” and “man” as the sources use them.

Read the original article on Verywell Health.