IBS: Causes, Risk Factors, Signs, And Symptoms

Irritable bowel syndrome (IBS) is a common condition, with between 7% and 16% of the US population suffering from symptoms. It is characterized by alterations in bowel habit, often alternating between constipation and diarrhea, abdominal pain, cramping, and flatulence.¹ ²

One of the requirements for the diagnosis is that there is no other organic pathology underlying the symptoms.

If you’ve been diagnosed with IBS or think you might have it, you may want to know what causes IBS and its risk factors.  Read on to find out more about the causes of IBS and what the first signs and symptoms are. 

Have you considered clinical trials for Irritable bowel syndrome (IBS)?

We make it easy for you to participate in a clinical trial for Irritable bowel syndrome (IBS), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

Causes of IBS

Although IBS was first recognized over 150 years ago, the exact cause for it is still unknown. It seems likely that IBS is multifactorial in origin, with many different factors contributing to the development of the syndrome.²

1. Anxiety and depression

IBS is classified as a functional bowel disorder. This means that some of the symptoms of IBS are caused by a dysregulation of your gut-brain interactions.³

There is a very complicated link between the brain and the gut—the gut is sometimes even called the second brain—and science is still uncovering all of the complexities involved in brain-gut interactions.

IBS has been linked to anxiety and depression. People who suffer from IBS have elevated levels of stress hormones in their blood, suggesting that they have an elevated response to stress.

There is also a well-recognized link between IBS and childhood trauma. However, in 50% of cases, IBS develops primarily in the gut and is followed by psychological symptoms such as anxiety and depression.

It’s most likely that IBS is not a problem with the gut or the brain alone, but rather a dysregulation of the communication between them.⁴

2. Altered gut microbiome

A study looking at the microbiome (colonies of bacteria resident naturally in your gut) of people with IBS found a correlation between the severity of IBS symptoms and reduced microbial diversity.

In simplified terms, what this means is that if you have fewer species of good bacteria living in your gut, you are more likely to have severe IBS. Unfortunately, no causative link has been found, so it’s not yet clear if the lack of bacterial diversity causes the IBS symptoms or if the IBS causes the lack of species of good bacteria.⁴

Your microbiome can be altered with dietary changes and certain probiotics, which might explain why some IBS sufferers find relief from these two interventions.

3. Infection and immune activation

Approximately one in ten patients can trace their IBS back to an episode of gastroenteritis (infectious diarrhea), and studies show that 3% to 36% of gut infections lead to persistent IBS.

Bacterial and parasitic infections are most likely to lead to persistent IBS. Viral gastroenteritis is less likely to lead to persistent IBS.

Infection causes chronic inflammation of the lining of the colon, which then leads to activation of immune cells - also known as ‘leaky gut.’

Immune activation can alter the release of serotonin in your gut. Serotonin is important because it plays a role in the sensory and motor modulation of your gut. This sounds complex, but in very simple terms, sensory functions of your gut include how pain is perceived, and motor functions of your gut include how quickly or slowly contents are moved through your intestines (too quickly causes diarrhea and too slowly causes constipation). Once you understand this, it's easy to see how changes in serotonin leading to alterations in sensory and motor function of the gut could trigger IBS symptoms.⁴ ⁵

4. Genetics

IBS can cluster in families, and in 2% of cases, there is actually a recognized genetic mutation responsible for IBS.⁴ As more and more genes are mapped, more genetic mutations responsible for IBS will likely be identified.

Congenital enzyme deficiencies such as sucrase-isomaltase (the enzymes necessary to break down sucrose and isomaltose) deficiency can also cause IBS. This makes sense as we know that people with lactose intolerance (deficient in lactase, which breaks lactose down) present symptoms similar to IBS when they eat dairy. 

Risk factors for IBS

Knowing the risk factors for IBS can help you identify whether it’s likely that your symptoms are caused by IBS.⁵ ⁶


IBS is more common in younger people and is seldom diagnosed after the age of 50. Over the age of 50, it’s more likely that your symptoms are triggered by an organic cause than IBS. In that case, serious diseases like colon cancer need to be excluded.


Females are more likely to be diagnosed with IBS than males. There also seems to be a link with estrogen therapy, with IBS being more common after estrogen therapy, before, or after menopause


Because genetic changes are responsible for some cases of IBS, if someone in your family has IBS, you may be at more risk of developing it. The exact nature of these changes is unclear and is under investigation.

Environmental factors may also contribute to IBS, so growing up in the same environment as someone with IBS may mean that you may be more likely to develop it.

Anxiety or depression

If you suffer from anxiety or depression, you may be more at risk of developing IBS. The reverse is also true: if you have IBS, you may be more likely to develop anxiety or depression.

History of childhood abuse

People with a history of childhood physical or sexual abuse have a higher risk of developing IBS.

Severe bacterial or parasitic gastroenteritis

Severe gastroenteritis can lead to persistent IBS.  Risk factors make it more likely that you will develop persistent IBS after an infectious bout of diarrhea, which include:

  • Prolonged duration of the initial gastroenteritis 

  • How toxic the bacteria is that causes the infection

  • Smoking 

  • Female gender 

  • Underlying depression  

  • Adverse life events in the three months preceding the infection

  • Antibiotic treatment for the infection

First signs and symptoms of IBS

It’s important to note that the symptoms are very similar no matter what the cause of your IBS—whether it’s an infection, genetic, abnormal gut microbiome, or the result of childhood trauma.

The most common symptoms of IBS are:

  • Abdominal pain, cramping, or bloating associated with bowel movements 

  • Changes in bowel movements such as alternating diarrhea and constipation, or diarrhea, or constipation

  • Bloating

  • Whitish mucus in your stool

  • Feeling as though you haven't completely evacuated your bowels after passing stool

Symptoms in women can be worse around the time of their period.

IBS does NOT cause the following signs and symptoms, and if you have them, you should see your doctor for further investigations because you may have a more serious condition:

  • Weight loss

  • Diarrhea at night

  • Rectal bleeding

  • Persistent pain that isn't relieved by passing gas or a bowel movement

The lowdown

Multiple factors contribute to the development of IBS. Anxiety, depression, altered gut microbiome, infection,  immune activation, and even genetics can all contribute to the development of IBS.

Most people who suffer from IBS usually experience abdominal pain, altered bowel habits, diarrhea, constipation, and bloating. If you suspect you may have IBS, it's best to see a doctor for a diagnosis because some of the symptoms can mimic more serious illnesses.

Have you considered clinical trials for Irritable bowel syndrome (IBS)?

We make it easy for you to participate in a clinical trial for Irritable bowel syndrome (IBS), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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