Irritable Bowel Syndrome: Symptoms, Causes, Diagnosis and Treatment
Updated October 2026
Abdominal pain, a bloated stomach, sometimes diarrhoea, sometimes constipation: with irritable bowel syndrome (IBS), your gut keeps playing up even though the usual tests show no other disease. The symptoms are real and often hard to live with, but they are not dangerous. This guide explains how to recognise IBS, how it is diagnosed and which treatments help, according to the current guidelines.
Key points
- Typical symptoms are recurring abdominal pain or discomfort linked to bowel movements. They often come with bloating, diarrhoea or constipation.
- Depending on the study and definition, about 4 to 11 per cent of adults have IBS. Women are affected almost twice as often as men.
- Diagnosis is based on the typical pattern of symptoms and a few targeted tests. Warning signs such as blood in your stool or unintentional weight loss do not fit IBS and can have another cause.
- The strongest evidence is for soluble fibre such as psyllium husk, a low FODMAP diet, peppermint oil, some medicines, gut-directed hypnotherapy and cognitive behavioural therapy (CBT).
- No single treatment works for everyone. Usually you need a combination, matched to your main symptoms.
What is IBS?
Irritable bowel syndrome (IBS) is a functional disorder of the gut. The gut is more sensitive than usual and works irregularly, even though tests show no signs of disease. That is why experts class IBS as a disorder of gut-brain interaction: the gut and the nervous system no longer work well together.
IBS at a glance
IBS is unpleasant and can severely restrict your everyday life, but it is not life-threatening. However, similar symptoms also occur with other conditions.
Symptoms: how to recognise IBS
The typical pattern is a mix of abdominal symptoms and changes in bowel habits that keeps coming back over months. Symptoms vary from day to day. Good and bad spells alternate, sometimes for no obvious reason.
Usually in the lower abdomen. The pain is linked to bowel movements, often gets worse after eating and tends to ease once you have been to the toilet.
Almost everyone with IBS knows the feeling of a swollen, tight stomach. Many also pass more wind than usual.
Mushy to watery stools, often with a sudden, strong urge to go.
Hard, lumpy stools, infrequent bowel movements and a lot of straining.
Diarrhoea and constipation can alternate. After a bowel movement, many people feel that their bowel has not emptied completely.
Clear or whitish mucus can occur with IBS. Blood, on the other hand, is not a symptom of IBS.
Many people also have symptoms outside the gut, such as tiredness, nausea, back pain or bladder problems.
Doctors distinguish four types of IBS, depending on which stool form is most common. They use the Bristol Stool Form Scale, which classifies stools from type 1 (hard lumps) to type 7 (watery). Only days with abnormal bowel movements count.
More than a quarter of bowel movements are hard or lumpy (types 1 and 2), and less than a quarter are mushy or watery (types 6 and 7).
More than a quarter of bowel movements are mushy or watery, and less than a quarter are hard or lumpy.
More than a quarter of bowel movements are hard or lumpy, and more than a quarter are mushy or watery as well.
Stools do not fit any of the three groups.
Your type can change over time and helps determine which medicines are an option. Classification based on Rome V (2026). In German, the types are abbreviated RDS-O, RDS-D, RDS-M and RDS-U.
Causes: why the gut overreacts
There is no single cause. Usually several factors come together, and the mix is slightly different for each person. These mechanisms are well researched:
Many people with IBS feel normal processes in the gut more strongly, such as gas or the stretching of the gut wall. Experts call this visceral hypersensitivity.
The gut and the brain are connected by nerves and chemical messengers such as serotonin. When this interaction is disrupted, pain perception and gut movement change.
The gut moves its contents along too quickly at some times and too slowly at others. This makes diarrhoea or constipation more likely.
More than 10 per cent of people develop IBS after a bout of acute gastroenteritis. Experts call this post-infectious IBS.
Many people with IBS have a different mix of gut bacteria. Whether this is a cause or a consequence is not yet clear.
Psychological stress can help trigger IBS and make flare-ups worse. Traumatic experiences such as violence or abuse almost triple the risk.
What about food? Food is usually not the cause, but it is a common trigger. Certain carbohydrates, known as FODMAPs, are poorly absorbed in the small intestine. They travel on to the large intestine, where they draw in water and are fermented by bacteria. An oversensitive gut can react to this with pain, bloating or diarrhoea. We explain exactly what FODMAPs are and how the FODMAP diet works in our article What are FODMAPs? True food allergies, on the other hand, are rare in IBS.
Warning signs: symptoms that do not fit IBS
The following symptoms are not typical of IBS. They can point to another condition, even if you have already been diagnosed with IBS.
The main warning signs
- Blood in your stool, bloody diarrhoea or black, tarry stools
- Unintentional weight loss
- Signs of anaemia such as paleness, shortness of breath or a pounding heart
- A lump or swelling in your abdomen that you can feel
- Fever, or symptoms that wake you up at night
- New, persistent changes in bowel habits from around the age of 50
- A family history of bowel cancer, ovarian cancer, coeliac disease or inflammatory bowel disease
In women, new and persistent bloating, especially from the age of 50, can in rare cases be a sign of ovarian cancer.
Diagnosis: how doctors identify IBS
IBS is no longer simply a diagnosis of exclusion. Doctors recognise it from the typical pattern of symptoms and carry out the tests that make sense in your case. Internationally, they use the criteria of the Rome Foundation. The fifth version, Rome V, was published in 2026:
Rome V criteria
The German S3 guideline defines IBS a little more broadly: the symptoms last longer than three months or keep coming back, are attributed to the bowel and usually come with changes in bowel habits. They are severe enough to significantly affect quality of life. And no other condition explains them better.
The usual steps are:
Medical history. Your doctor asks about the type and duration of your symptoms, your bowel habits, any medicines you take and illnesses in your family. A symptom diary helps.
Physical examination. This includes feeling your abdomen and, depending on your symptoms, a rectal examination.
Blood tests. These usually include a full blood count, the inflammation marker CRP and a test for coeliac disease.
Stool sample. If you have diarrhoea, faecal calprotectin is usually measured. A normal result makes inflammatory bowel disease very unlikely. If diarrhoea persists, a test for the Giardia parasite is also worthwhile.
Colonoscopy, if needed. A colonoscopy is mainly needed if there are warning signs, for bowel cancer screening, or to rule out microscopic colitis if diarrhoea persists. Without warning signs, it rarely finds anything.
Breath tests for lactose or fructose and tests for small intestinal bacterial overgrowth (SIBO) are not necessary for everyone. The Rome criteria do not recommend them routinely. Whether one is useful depends on the symptoms.
Conditions that can cause similar symptoms include coeliac disease, lactose intolerance, Crohn’s disease and ulcerative colitis, microscopic colitis, bile acid malabsorption, thyroid disorders, endometriosis and side effects of medicines. Around a quarter of people with diarrhoea-type IBS have bile acid malabsorption, which has its own specific treatment.
Treatment: what helps with IBS
There is no treatment that works for everyone. The guidelines recommend starting with a clear explanation of the condition, exercise and simple dietary rules. If that is not enough, targeted treatments for your main symptoms come next. Give each treatment a few weeks and, if possible, change only one thing at a time. That way you can see what works.
| Main symptom | Diet and daily life | Medicines and therapy |
|---|---|---|
| Abdominal pain and cramps | Soluble fibre, a low FODMAP diet, exercise | Peppermint oil, antispasmodics such as hyoscine butylbromide, low-dose amitriptyline, gut-directed hypnotherapy or CBT |
| Bloating and wind | A low FODMAP diet, oats and linseed, exercise | Peppermint oil, treating constipation or diarrhoea. There is little research on bloating. |
| Diarrhoea | A low FODMAP diet, cutting down on coffee, alcohol and sorbitol | Loperamide, the antibiotic rifaximin, treatment for bile acid malabsorption if confirmed |
| Constipation | Psyllium husk (increase slowly), plenty of fluids, exercise | Macrogol, and for severe symptoms prescription medicines such as linaclotide |
Based on Rome V (2026), the British Society of Gastroenterology guideline (2021) and NICE. Some of these medicines are not specifically licensed for IBS.
In studies, soluble fibre such as psyllium husk eased overall symptoms and pain. Start with about 3 to 4 g a day, increase the amount slowly and drink enough fluids with it. Wheat bran, on the other hand, does not help and can make bloating worse.
Enteric-coated peppermint oil capsules relax the muscles of the gut. In studies, they helped with pain and overall symptoms. A common side effect is heartburn.
Antispasmodics can ease cramps, while loperamide mainly reduces how often and how urgently you need to go. Low-dose amitriptyline, 10 to 30 mg in the evening, is well researched. At this dose, it does not work as an antidepressant but acts on how pain is processed between the gut and the brain. Common side effects are a dry mouth and tiredness.
The effect depends on the bacterial strain, and study results are mixed. If you try one, take it at the recommended dose for at least 4 weeks and stop after 12 weeks at the latest if nothing improves. Some people get more bloating from them.
Diet and IBS
Many people with IBS notice that their symptoms get worse after eating. The guidelines therefore recommend a two-step approach. First come simple rules, which are enough for some people:
What often helps
- Eating regular meals and taking your time over them
- Drinking at least 8 glasses or cups of fluid a day, mainly water
- For wind and bloating, oats and up to 1 tablespoon of linseed a day
- Soluble fibre such as psyllium husk, increased gradually
Better to cut down on
- Coffee and black tea, no more than 3 cups a day
- Alcohol and fizzy drinks
- More than 3 portions of fresh fruit a day
- Wheat bran and highly processed foods
- Sorbitol if you have diarrhoea, for example in sugar-free chewing gum and sweets
If these rules do not help enough, the next step is a low FODMAP diet. It is the best-studied dietary treatment for IBS. According to Monash University, which developed the approach, symptoms improve in around three out of four people with IBS. The diet is not meant to be permanent and has three phases:
1Cut out
2 to 6 weeks
You eat a low FODMAP diet and see whether your symptoms ease. Our FODMAP list shows which foods fit.
2Reintroduce
usually 8 to 12 weeks
You test the FODMAP groups one at a time. Our reintroduction test plan shows you how.
3Personalise
long term
You go back to eating as varied a diet as possible and only limit what causes you symptoms.
A test for coeliac disease is only reliable while you are eating wheat, rye and barley as usual. The diet may not be suitable if you have or have had an eating disorder.
Onions, garlic and enzymes in IBS
Onions and garlic are among the biggest everyday sources of fructans and a common trigger in IBS. They also hide in many ready-made products, often as a powder or behind the word ‘spices’. You do not have to give up the flavour, though. Fructans dissolve in water but not in oil, so garlic-infused oil tastes of garlic and stays low FODMAP. The green parts of spring onions and leeks work too. For the full flavour, there are certified onion and garlic replacers:
FreeFOD Onion Replacer1 tsp replaces one onion
FreeFOD Garlic Replacer1 tsp replaces one clove
Fody Garlic-Infused Olive Oilgarlic flavour without fructans
FODZYME On-the-go Kitenzymes for eating out
Enzymes and IBS: Digestive enzymes can break down certain FODMAPs before they reach the large intestine. For lactose intolerance, the evidence for lactase is good. FODZYME also contains enzymes for fructans and GOS and is handy when you eat out and do not know what is in your food. Research on these enzymes is still limited, and they do not change the underlying cause of IBS. Read more in our article on reintroduction.
You will find practical everyday recipes for IBS in our recipe collection.
Mind, exercise and everyday life
Because the gut and the brain work closely together, treatments that act on the mind can help too. Gut-directed hypnotherapy and cognitive behavioural therapy are among the best-studied psychological treatments for IBS. This does not mean the symptoms are imaginary. These treatments target the link between the gut and the brain.
Over several sessions, you learn to calm your gut using relaxation and mental imagery. It is also available as an audio programme or app.
You learn how thoughts, stress and behaviour affect your symptoms, and practise new strategies. Guided self-help programmes can also be effective.
Regular exercise such as brisk walking, cycling or yoga can ease symptoms a little.
For a while, note down what you eat, your bowel movements, symptoms, sleep and stress. This helps you spot patterns. You can also use the Monash FODMAP app for this.
In Germany: If you have been diagnosed with IBS, you can get the app ‘Cara Care für Reizdarm’ on prescription. It combines a low FODMAP diet, cognitive behavioural therapy and gut-directed hypnotherapy, and it is permanently approved as a digital health application (DiGA). Statutory health insurance covers the cost.
The guidelines recommend psychological treatment if other therapies have not helped enough after about a year, or earlier if you would like it.
Frequently asked questions about IBS
Is IBS dangerous?
No. IBS does not damage the gut and is not life-threatening. It can, however, severely restrict your everyday life, so it deserves proper treatment. Warning signs such as blood in your stool or unintentional weight loss do not fit IBS and can have another cause.
What do stools look like with IBS?
It depends on the type. With diarrhoea-type IBS, stools are mushy to watery. With the constipation type, they are hard and lumpy, and with the mixed type, they alternate between the two. Mucus can occur. Blood or black stools do not fit IBS and can have another cause.
What helps quickly during an IBS flare-up?
Many people find warmth on the stomach, rest and small, light meals soothing. Peppermint oil or an antispasmodic can ease cramps, and loperamide can help with acute diarrhoea. How long a flare-up lasts varies a great deal. If flare-ups become more frequent, longer-term treatment may be an option.
Can IBS go away?
IBS is usually long-lasting and comes and goes in phases. In some people, symptoms become less frequent over time. In others, they persist for years. The aim of treatment is to ease the symptoms enough for you to live well with them.
What should I avoid eating with IBS?
There is no general list of forbidden foods, because triggers vary from person to person. Common culprits are onions, garlic, wheat, pulses, some fruits, lactose and sugar alcohols. A low FODMAP diet followed by reintroduction helps you find out what you tolerate. Our FODMAP list gives you an overview.
Does a gluten-free diet help?
If you have IBS but not coeliac disease, the guidelines do not recommend a gluten-free diet. With wheat, it is usually the fructans that cause symptoms, not the gluten. If you cut out wheat before a coeliac test, the result may be a false negative. Read more in our article FODMAP vs gluten.
Sources: DGVS and DGNM, German S3 guideline on irritable bowel syndrome (2021) · Rome Foundation, Rome V: Bowel Disorders (Gastroenterology 2026) · British Society of Gastroenterology, Guidelines on the management of IBS (Gut 2021) · NICE, Irritable bowel syndrome in adults (CG61) · Monash University, About FODMAPs and IBS · NHS, Symptoms of IBS · BfArM, DiGA directory: Cara Care für Reizdarm
Photo: Sasun Bughdaryan on Unsplash
