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What is irritable bowel syndrome (IBS)?

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Irritable bowel syndrome (IBS) is one of the most common digestive disorders. It is characterised by recurrent abdominal pain associated with changes in bowel habits, such as diarrhoea, constipation, or both. These symptoms are caused by changes in the way the gut and brain communicate with each other.

IBS explained in first person

Professionals and patients explain how you live with the disease

Irritable bowel syndrome (IBS), commonly known as a sensitive or irritable bowel, is a disorder within a group of conditions known as disorders of gut–brain interaction (DGBI). This term has replaced the previously used term “functional gastrointestinal disorders”. 

The gut-brain axis: How does the gut microbiota communicate with the brain?

The gut-brain axis is a two-way communication network between the digestive system and the brain, in which the gut microbiota plays an important role. Communication along this axis takes place through a combination of nerve, hormonal, immune and metabolic signals, allowing a constant exchange of information between the two. The gut also contains a complex network of nerves called the enteric nervous system. This is why the gut is sometimes referred to as the “second brain” in information aimed at the general public. Through this communication network, the brain can influence how the gut functions, while the gut and its microbiota can, in turn, send information to the brain.

This interaction between the gut and the brain helps explain why factors such as stress, emotions, sleep and lifestyle habits can affect digestive symptoms. In people with irritable bowel syndrome (IBS), changes in communication between the gut and brain may contribute to symptoms such as abdominal pain, bloating, diarrhoea or constipation. As a result, managing IBS involves looking beyond the gut itself and considering factors such as diet, physical activity, rest and emotional wellbeing.

Irritable bowel syndrome (IBS) is a chronic condition characterised by recurrent episodes of abdominal pain associated with bowel movements and changes in the frequency or consistency of stools. 

Depending on the predominant pattern of symptoms, IBS is classified as: 

  • IBS with constipation (IBS-C)
  • IBS with diarrhoea (IBS-D) 
  • IBS with mixed bowel habit (IBS-M), when episodes of constipation and diarrhoea alternate. 

Although IBS is a benign condition, it can have a significant impact on quality of life. Symptoms may vary over time, with periods of improvement alternating with periods of increased severity. 

How many people does it affect?

Irritable bowel syndrome (IBS) is one of the most common digestive disorders. It is estimated that between 5% and 10% of the general population will experience IBS at some point in their lives. 

In Spain, the prevalence is estimated to be around 8%. IBS is also one of the most common reasons for seeking medical advice about gastrointestinal symptoms in primary care, accounting for approximately 30% of consultations for these symptoms. 

IBS can develop at any age and affects both men and women. However, it is more common in women, particularly between the ages of 20 and 40

Read more Causes and risk factors

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Published: 25 September 2026
Updated: 25 September 2026

The donations that can be done through this webpage are exclusively for the benefit of Hospital Clínic of Barcelona through Fundació Clínic per a la Recerca Biomèdica and not for BBVA Foundation, entity that collaborates with the project of PortalClínic.

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