Irritable bowel syndrome (IBS) is a common, long-term condition in which recurring belly pain goes hand in hand with changes in your bowel habits: diarrhea, constipation, or both. It is a disorder of gut–brain interaction, meaning the gut and the nervous system communicate abnormally, not a disease that inflames or damages the bowel. Doctors diagnose it from your symptom pattern plus a few simple tests, and diet, fiber, psychological therapies and medicines can all help.[1][2]
IBS is one of the most common digestive conditions seen by doctors in both primary and specialist care.[2] This page covers what it is, how it is diagnosed, what is thought to cause it, and how it is treated.
What are the symptoms of IBS?
The core symptom is abdominal pain that is linked to your bowels: it is related to having a bowel movement, or it comes with a change in how often you go or what your stool looks like.[1][3] Common features include:
- Abdominal pain or cramping that is tied to bowel movements.
- Diarrhea, constipation, or a mix of both, with stools that may be hard and lumpy or loose and watery.
- Bloating and abdominal distension (a visibly swollen belly). These are common enough that the standard IBS severity score counts distension as one of its five items.[5]
Symptoms usually come and go. In most people IBS follows a relapsing and remitting course,[1] and flare-ups can be triggered by stress, other illnesses, medicines and, often, by eating.[2]
Just as important is what IBS does not cause. Blood in your stool, unintentional weight loss or a family history of inflammatory bowel disease or celiac disease are reasons for further tests, not features of IBS.[1] See IBS red flags for the full list.
What are the Rome IV criteria for IBS?
Doctors and researchers define IBS using the Rome IV criteria, published by the Rome Foundation in 2016.[3] You meet them if you have:
- Recurrent abdominal pain, on average at least 1 day per week in the last 3 months, associated with two or more of the following:
- it is related to defecation;
- it is associated with a change in how often you have a bowel movement;
- it is associated with a change in the form (appearance) of your stool.
- These criteria have been met for the last 3 months, with symptoms starting at least 6 months before diagnosis.
These criteria appear in both the American College of Gastroenterology (ACG) and British Society of Gastroenterology (BSG) guidelines.[4][2]
What are the types of IBS?
IBS is divided into four subtypes based on your stool consistency, measured with the Bristol Stool Form Scale, which runs from type 1 (separate hard lumps) to type 7 (watery). The percentages refer to bowel movements on days when your stools are abnormal.[4][2]
| Subtype | Main pattern | Rome IV rule |
|---|---|---|
| IBS-C | Constipation | More than 25% of bowel movements are type 1 or 2, and fewer than 25% are type 6 or 7 |
| IBS-D | Diarrhea | More than 25% are type 6 or 7, and fewer than 25% are type 1 or 2 |
| IBS-M | Mixed | More than 25% are type 1 or 2 and more than 25% are type 6 or 7 |
| IBS-U | Unclassified | Meets the IBS criteria but doesn't fit any of the other three |
The ACG recommends judging your subtype from a daily stool diary kept for 2 weeks while you are off medicines that affect bowel habits. The subtype matters because most IBS medicines were developed for one specific subtype.[4]
How common is IBS?
How common IBS looks depends heavily on how it is defined and how people are surveyed:
- A 2012 meta-analysis of 80 study populations with 260,960 people found a pooled prevalence of 11.2%, using older criteria. It ranged from 1.1% to 45.0% between countries. IBS was more common in women than men (odds ratio 1.67) and less common in people over 50.[6]
- The 2021 Rome Foundation Global Study surveyed 73,076 adults in 33 countries. Using the stricter Rome IV criteria, 4.1% of internet respondents and 1.5% of people interviewed in person had IBS. With the older Rome III criteria the figures were 10.1% and 3.5%.[7]
A reasonable summary is that IBS affects roughly 5% to 10% of otherwise healthy people at any one time. It is more common in young adult women and in people with coexisting psychological conditions.[1]
What causes IBS?
There is no single cause. IBS is now classed as a disorder of gut–brain interaction (previously called a "functional" gastrointestinal disorder).[2][8] The best-established mechanisms are:
- Gut–brain miscommunication. Signals between the gut and the brain are disordered, so the brain processes gut sensations differently.[1]
- Visceral hypersensitivity, meaning the nerves of the gut are oversensitive, so normal stretching from gas or stool is felt as pain or bloating. UK guidelines describe this as the main mechanism in IBS and the target of many treatments.[2]
- Altered motility, meaning the muscle contractions that move food along are faster or slower than usual, which shows up as diarrhea or constipation.[1][8]
- Microbiome and immune changes. Differences in gut bacteria and subtle changes in the gut lining and immune activity have been found, but these findings are less consistent.[1]
The best-described risk factor is a gut infection, which leads to post-infectious IBS.[1] In a meta-analysis of 45 studies covering 21,421 people, 10.1% had IBS 12 months after infectious enteritis, and their risk was 4.2 times that of people without such an infection. Risk was higher in women, in people given antibiotics during the infection, and in people with anxiety or depression.[9]
How is IBS diagnosed?
Guidelines recommend a positive diagnosis, not a "diagnosis of exclusion" that requires ruling out everything else first. The ACG found that a careful history, a physical exam and a few targeted tests are enough in most people, and this gets them onto treatment sooner.[4] Typical first tests are:
- a full blood count, C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR), and celiac disease blood tests;[2]
- fecal calprotectin, a stool marker of bowel inflammation, if you have diarrhea (UK guidance specifies people under 45), to help rule out inflammatory bowel disease.[2][4]
Routine colonoscopy isn't recommended for people under 45 with IBS symptoms and no warning signs, and neither are routine stool tests for infections or food allergy and sensitivity tests.[4] If you have alarm features, your doctor will investigate further. You can read how IBS differs from Crohn's disease and ulcerative colitis in IBS vs IBD.
How is IBS treated?
Treatment is chosen around your main symptoms and subtype. A clear explanation of IBS as a gut–brain disorder is itself part of treatment,[2] and guidelines describe several options.
Lifestyle and diet
- Regular exercise may help, particularly for constipation.[2]
- Soluble fiber such as psyllium (ispaghula) can improve overall symptoms and pain. Insoluble fiber such as wheat bran can make symptoms worse.[2][4]
- The low-FODMAP diet limits FODMAPs (fermentable oligo-, di- and monosaccharides and polyols), which are carbohydrates that draw water into the gut and are fermented by gut bacteria. The ACG recommends a limited trial. The BSG says it should be supervised by a trained dietitian, with FODMAPs reintroduced according to tolerance, and that people at risk of overly restrictive eating should be screened out first.[4][2] If you are pregnant, or this is for a child, talk to a doctor before changing your diet. See the low-FODMAP diet for how the phases work.
Psychological therapies
IBS-specific cognitive behavioral therapy (CBT) and gut-directed hypnotherapy are recommended for overall IBS symptoms.[2][4] They act on the gut–brain axis. Being offered them doesn't mean your symptoms are "all in your head."
Medicines
- Peppermint oil may ease overall symptoms (supported by both guidelines).[2][4]
- Antispasmodics divide the guidelines. The BSG makes a weak recommendation for certain antispasmodics, while the ACG recommends against them for overall IBS symptoms.[2][4]
- Tricyclic antidepressants are used as gut–brain neuromodulators, medicines that act on the communication between gut and brain. Being prescribed one doesn't mean your doctor thinks you're depressed. Both guidelines recommend them.[2][4]
- Subtype-specific medicines are also available. For IBS-C these include chloride channel activators and guanylate cyclase activators, and for IBS-D the antibiotic rifaximin, among others.[4]
- Probiotics divide the guidelines too. The ACG suggests against them, while the BSG says a 12-week trial is reasonable, stopping if they don't help.[4][2]
Your doctor can help you choose and combine these. Keeping a record of meals, symptoms and stool types makes those conversations far more productive. IBS Clue, an iPhone app coming soon, lets you log meals, quick symptom check-ins and Bristol stool types, and export a PDF report for your doctor. It is a self-tracking tool, not a diagnostic one. To measure how severe your symptoms are over time, see the IBS Symptom Severity Score.