The exact cause of irritable bowel syndrome (IBS) is not completely understood. Sometimes it develops after a severe bout of infectious diarrhea or trauma, but in many cases, there is no specific incident. Researchers suggest causes may be some interplay between gut motility problems, pain sensitivity, inflammation, and how the brain and the gut "communicate."

Genetics, prior adverse life experiences, and some mental health conditions may predispose someone to IBS. Other factors that may cause or exacerbate IBS symptoms include stress, menstrual cycle hormones, smoking, and diet.

Common Causes

Overall, researchers are pursuing several areas in which there may be a difference between the bodies of people who have IBS and those who do not have the condition. These include motility, visceral hypersensitivity, inflammation, and gut bacteria.

Motility

Motility refers to the movement of the smooth muscle of the digestive tract. Although research has not shown consistent results, there is some evidence that the speed of this movement is altered in both the colon and the small intestines of individuals with IBS.

Contractions that are faster than usual are seen in some individuals who suffer from diarrhea-predominant IBS (IBS-D), whereas the muscle movements are too slow in some individuals who suffer from constipation-predominant IBS (IBS-C).

Visceral Hypersensitivity

Visceral hypersensitivity is a heightened sense of pain in the internal organs of the body. Studies have shown that many patients with IBS experience pain in the rectum at a different threshold level than people who do not have the disorder.

It is thought that this difference in pain perception is the result of a process in which the nerves of the gut become over-sensitized to stimulation.

Inflammation

By definition, IBS does not present with visible inflammation. However, though it may not be visible during routine diagnostic testing, it may still be involved.

Evidence of the possibility of low-grade chronic inflammation on a cellular level in some individuals who suffer from IBS is beginning to build. This inflammation is thought to most likely be associated with cases in which IBS was preceded by a bout of gastroenteritis, a condition classified as post-infectious IBS (IBS-PI).

Gut Bacteria

Although not as clear-cut as it sounds, the complicated nature of gut bacteria is better understood when the microorganisms are classified as "good" (such as probiotics) and "bad" (bacteria associated with infection and inflammation).

Research focus on gut bacteria has begun to offer some evidence that there is a difference between the bacterial makeup of some IBS patients and those who do not have the disorder. Particular attention has been given to the role of bacteria in the small intestine as a contributor to IBS—namely, small intestine bacterial overgrowth (SIBO).

The Brain-Gut Connection

The enteric nervous system is a network of nerves that directs the processes of digestion and is in close communication with the brain. This interaction is seen most clearly during the stress response.

There is evidence that dysfunction in the interactions between the gut and the brain may underlie the motility disturbance and visceral hypersensitivity that result in IBS symptoms.

This dysfunction is thought to be related to an imbalance in levels of particular neurotransmitters, which is why people with IBS often find relief from symptoms when taking antidepressants that target specific neurotransmitters.

Hormones

Women are more likely to have IBS, which implies that changes in hormones play a role in developing the condition. Consequently, many women find that their IBS symptoms are worse during or around their menstrual cycles.

IBS also is more common in people who have anxiety, depression, and other mental health issues. A history of physical, sexual, or emotional abuse also increases the likelihood of IBS.

Genetics

Initial research suggests that there is a genetic component of IBS as well, since it tends to run in families.

According to a study featured in Gastroenterology, some people with IBS have a specific genetic defect (mutation) of the SCN5A gene that causes their condition. When this mutation is present, it causes people to experience a disruption in bowel function. During the initial study, researchers found that this gene mutation was present in 2.2% of IBS patients. Later, these results were confirmed in a genome-wide association study.

Further studies of the genes associated with IBS may help point to the underlying causes of the condition.

Lifestyle Risk Factors

It is no secret that stress can wreak havoc on your body. The body's stress response, in fact, can impact the development of IBS (as is evident with the brain-gut connection).

The evidence is stronger for anxiety and depression as risk factors for IBS, including post-infectious enteritis IBS. Whether or not a stressful lifestyle leads to developing IBS—rather than triggering symptoms or exacerbations once you have the condition—is less clear, however.

Smoking, drinking alcohol, obesity, lack of exercise, and poor diet can increase IBS flare-ups. Maintaining a healthy lifestyle may help prevent exacerbations of your condition.

A Word From Verywell

When comes to an IBS diagnosis, it can be frustrating to try to cope with an issue when you do not know exactly what is causing it. But, by reading more about IBS and talking regularly with your doctor, you will find ways to deal with the condition and still live a normal, active life. Eventually, you will discover things that work for you—whether it is meditation to relieve stress, adhering to a special diet, or a combination of the two. Once you reach that point, your IBS will just be something you live with and not something that controls your life.