No one knows what causes irritable bowel syndrome (IBS). Right now, researchers believe that IBS develops due to problems with how your gut and brain interact with each other. Research is ongoing to confirm this and to understand exactly what’s going on when you experience IBS symptoms.

If you’ve been diagnosed with IBS, it’s important to get as clear a picture as possible about what might be going on with your body. That way, you can work with your gastroenterology team to find out what type of IBS you have and then look for the best treatment options for you. These can help you manage symptoms and feel your best.

Causes of IBS

Researchers have some ideas about what goes on in your body when you’re living with IBS. Here’s what we know contributes to causing IBS.

1. Muscles in Your Intestines May Work Too Hard or Not Enough

After you eat, food is moved through your digestive tract by layers of muscles. The muscles contract and relax, squeezing your food through your intestines. When you live with IBS, the muscles in your intestines may contract too much or not enough. If they contract too much or the contractions are too strong, you might have gas, diarrhea, cramping, or abdominal pain or experience bloating. If they aren’t contracting enough or the contractions are weaker than they should be, you might have hard stools and constipation.

While this explanation provides some clarity, it doesn’t explain why some people who live with IBS experience abdominal pain even when there’s a normal amount of food or gas in their gastrointestinal tract.

2. Nerves in Your Digestive System May Be Overly Sensitive

Some health experts think that the digestive changes associated with IBS happen because of issues with the nerves in your digestive tract, rather than just the muscles. These nerves send and receive signals via your central nervous system that tell your brain what’s going on in the digestive tract and if it should be experienced as painful or uncomfortable.

You may have nerves in your digestive tract that are very sensitive. Thus, you may experience things as uncomfortable or even painful that other people wouldn’t. When normal things like gas or poop are present in your digestive tract, your nerves may tell your brain that it needs to react more than normal. This could lead to constipation and/or diarrhea (or other changed bowel habits) that many people with IBS face.

3. Your Gut Bacteria May Not Be Balanced

Everyone’s gut contains bacteria that help break down the food you eat. The numbers and kinds of bacteria in your gut make up your gut microbiota. The microbiota is different in people who are living with IBS. There are different bacteria and/or different levels of certain bacteria present that show up in people without a diagnosis of IBS. Researchers don’t yet know if this imbalance is a cause of IBS or if it’s caused by something else and adds to the common symptoms of IBS.

4. You May Have Food Intolerances

In some people, IBS seems to be connected to being allergic or intolerant to certain foods. Researchers don’t know much about this, except that these allergies or intolerances seem to lead to IBS in some people. They don’t know if the allergies or intolerances are causing symptoms of irritable bowel syndrome or if both sets of digestive issues are symptoms themselves. Together, they might point to something else going on in the body. You can ask your gastroenterologist whether dietary changes might help with IBS symptoms.

Risk Factors Associated With IBS

While we don’t know exactly what causes IBS, we do know that some people are at a higher risk of developing it than others. Below are some IBS risk factors that have been identified by researchers.

1. Gender

IBS occurs almost twice as often in women as it does in men. Researchers don’t know what specifically puts women at a higher risk for IBS. Getting estrogen therapy raises a woman’s risk for IBS, so hormonal changes may be partially responsible.

2. Genetics

There are several genetic changes that are associated with IBS. Genetic changes are inherited from your parents, so IBS may tend to run in certain families. Just because you have a family history of IBS doesn’t mean you’ll develop it, but you may have genetic changes that make it more likely. For instance, your genes may make it more likely that your intestines will be inflamed, which could lead to IBS.

3. Mental Health

People who live with several mental health challenges, including anxiety and depression, are more likely to be diagnosed with IBS. Post-traumatic stress disorder and disorders affecting how, when, and how much you eat are also connected to a higher risk of IBS. Once again, researchers don’t fully understand the connection between these and IBS. They only know that some people are more likely to be diagnosed than others.

4. Gastroenteritis

Dealing with a condition called gastroenteritis makes it significantly more likely that you’ll later be diagnosed with IBS, too. This is usually a virus you get that affects your intestines. Many people refer to gastroenteritis as stomach flu. It causes digestive symptoms, such as cramps, nausea, and changes in bowel movements (like diarrhea). While most people get over gastroenteritis without any problems, it can lead to IBS.

5. Food and Beverages

Eating a lot of food that’s processed, fatty, or both can make it more likely that you’ll be diagnosed with IBS. Similarly, drinking alcohol is a risk factor. This doesn’t mean that avoiding these foods and abstaining from alcohol will prevent IBS. It does mean that changing your diet might lower your overall risk.

6. The Environment You Live In and Grew Up In

The environment you live in now and your childhood environment may be risk factors for IBS. Smoking, being exposed to pollution in the air, and owning a pet are among these risk factors. Similarly, if you’ve experienced physical, sexual, or emotional abuse, you might also have a higher risk.

7. Socioeconomic Factors

Some risk factors for IBS are related to your relative wealth or poverty, as well as to what you do for work. Living in a family that’s financially well off or one that has mental health or substance use problems both raise your risk for IBD. Doing shift work, having a low income, and having a high workload could also put you at risk. Not getting enough quality sleep and having certain ongoing health conditions — which often involve frequent visits to a healthcare provider — may also raise your risk for IBS.

8. Other Diagnoses

Certain diagnoses and symptoms that aren’t directly associated with IBS could raise your risk of developing it. These include asthma, diabetes, fibromyalgia, sleep disorders, liver diseases, and any chronic disease. Aspects of medical history, such as testing positive for certain antibodies (immune proteins) in your blood, having had an abdominal surgery, and having diarrhea for more than seven days, can also raise your risk. Your gastroenterology team will likely ask you about your health history to better understand what might have led to IBS in your body.

IBS Triggers

Triggers are different from both causes and risk factors. Triggers don’t cause the disease itself, but they may cause IBS flare-ups. Stress, hormonal changes, and eating certain foods are the most common triggers.

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