Bloating
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Bloating: Causes, Red Flags and What to Do About It
A UK clinical guide to a bloated stomach — the everyday causes, the conditions behind persistent bloating, and the pattern of symptoms that needs a doctor rather than a diet change.
Part of the Access Doctor Conditions Library.
When bloating is an emergency: call 999 for sudden severe abdominal pain, a rigid or exquisitely tender abdomen, vomiting blood or material that looks like coffee grounds, black tarry stools, or a swollen abdomen with vomiting and an inability to pass wind or stool at all. These suggest obstruction, perforation or bleeding rather than ordinary bloating.
Key fact: Bloating is a symptom, not a diagnosis, and the useful question is never “how bad is it?” but “what is the pattern?” Bloating that has been coming and going for years, builds through the day and is gone by morning is almost always functional. Bloating that is new, persistent, present on waking and slowly getting worse is the pattern that needs assessing — and in women over 50, NICE has a specific rule for it.
What bloating actually is
Bloating is the sensation of pressure, fullness or trapped wind in the abdomen. It has three separate ingredients, and most people have some combination of all three.
Gas volume
Air swallowed while eating, drinking or talking, plus the hydrogen and methane produced when gut bacteria ferment carbohydrate that has not been absorbed higher up.
Gut transit
How fast contents move through. Slow transit and loaded stool in the colon leave more time for fermentation and less room for everything else.
Gut sensitivity
How loudly the gut reports what is happening. In visceral hypersensitivity a normal volume of gas is felt as painful distension — the volume is ordinary, the perception is not.
This is why two people with identical amounts of intestinal gas can have completely different experiences, and why “get rid of the gas” is rarely the whole answer. There is also a fourth, mechanical ingredient: in some people the diaphragm contracts downwards and the abdominal wall relaxes outwards in response to normal gut contents, pushing the belly forwards. That reflex, known as abdomino-phrenic dyssynergia, explains the dramatic visible swelling some people develop within minutes of a meal.
Bloating vs distension vs weight gain
Three different things get called bloating, and separating them is the fastest way to work out what you are dealing with.
| What it is | Typical pattern | What it points to | |
|---|---|---|---|
| Bloating | The feeling of fullness or tightness | Comes and goes, often meal-related | Gas, gut sensitivity, functional causes |
| Distension | A measurable increase in girth — the waistband moves | Builds through the day, flat on waking | Gas volume, constipation, IBS |
| Persistent distension | Girth increased and staying increased | Present on waking, does not settle overnight, progressive | Needs assessment — fluid, mass or organ cause |
The overnight test: functional bloating almost always improves after a night’s sleep, because the gut empties and gas is passed. A swollen abdomen that is just as big when you wake as when you went to bed, and that stays that way for weeks, is the single most useful thing you can report to a clinician.
The causes at a glance
Bloating has a short list of common causes and a longer list of uncommon ones. The common list accounts for the overwhelming majority of cases.
| Cause | Clues that point to it |
|---|---|
| Diet and swallowed air | Clearly meal-related; fizzy drinks, beans, pulses, onions, cruciferous vegetables, sweeteners, eating fast |
| Constipation | Straining, hard or infrequent stools, incomplete emptying, worse the longer it goes on |
| IBS | Abdominal pain relieved by opening bowels, altered stool form or frequency, builds through the day, years of it |
| Food intolerance | Reproducible with a specific food — dairy, wheat, high-fructose foods, sugar alcohols |
| Coeliac disease | Bloating with tiredness, anaemia, mouth ulcers, weight loss or diarrhoea; family history |
| Reflux and indigestion | Belching, upper abdominal burning, early fullness, worse lying down |
| Hormonal and cyclical | Tracks the menstrual cycle; worst in the days before a period |
| Gynaecological | Pelvic pain, pain during sex, heavy periods, urinary urgency; persistent rather than cyclical |
| Medicines | Started or increased recently — GLP-1 weight loss medicines, opioids, iron, some antidepressants |
| Serious causes | Persistent, progressive, present on waking, with weight loss, bleeding or a change in bowel habit |
Food, fibre and fizz
The most common cause of bloating is the ordinary one: fermentable carbohydrate reaching the colon, where bacteria turn it into gas. Beans, lentils, onions, garlic, wheat, cabbage, sprouts, cauliflower, apples, stone fruit and the sugar alcohols in sugar-free gum and mints are the usual suspects. Fizzy drinks add gas directly. Eating quickly, talking while eating, chewing gum and drinking through a straw all add swallowed air.
Fibre is more nuanced than the headlines suggest. Insoluble fibre — bran, wholegrain cereals, skins and stalks — can make bloating worse in people with IBS, while soluble fibre such as oats, psyllium (ispaghula), linseed and the flesh of fruit tends to help. Increasing fibre suddenly reliably makes bloating worse for a couple of weeks, whichever kind it is, which is why the advice is to build up slowly and drink more water alongside it.
Before you cut anything out permanently: if wheat is one of your triggers, get tested for coeliac disease before you exclude gluten. Both the blood test and the biopsy depend on your immune response to gluten, so a gluten-free diet can hide the diagnosis for months.
Constipation: the most treatable cause
Constipation is the most common reversible cause of bloating and also the most commonly missed, because people rule it out on frequency alone. You can open your bowels every single day and still be constipated if the stools are hard, difficult to pass, or leave a sense of incomplete emptying. A loaded colon takes up room, slows transit, and gives bacteria longer to ferment — three separate reasons for a bigger, tighter abdomen.
It is worth treating properly before you conclude that anything else is going on. That usually means more fluid, more soluble fibre, regular movement, and where needed a laxative chosen for the problem: a bulk-forming laxative such as ispaghula for low-fibre stools, an osmotic such as macrogol or lactulose for hard stools, and a stimulant only for short-term rescue. A pharmacist can match the laxative to the stool type, which matters more than the brand.
Worth knowing: a change in bowel habit that has lasted six weeks or more, particularly over the age of 60 or alongside rectal bleeding or weight loss, is not simple constipation and should be assessed by a GP rather than self-treated.
Irritable bowel syndrome
IBS is the most common medical explanation for long-standing bloating, affecting somewhere between one in ten and one in five UK adults. NICE defines it as abdominal pain or discomfort that is either relieved by opening the bowels or associated with a change in stool frequency or form, plus at least two of: altered stool passage such as straining or urgency, bloating or visible distension, symptoms made worse by eating, and the passage of mucus.
The bloating of IBS has a recognisable rhythm: flat in the morning, building through the day, worse after meals, often dramatic by the evening, and back to baseline by the next morning. It is genuinely uncomfortable but it is not dangerous, and it does not cause weight loss, bleeding or anaemia — which is exactly why those features change the picture and prompt investigation.
We cover the condition in full, including subtypes, the low FODMAP approach and the medicines used, on our irritable bowel syndrome page. Antispasmodics are the usual first medicine for cramping and bloating — mebeverine and hyoscine butylbromide are both used — and enteric-coated peppermint oil has reasonable evidence for bloating and abdominal pain specifically.
An important exception: NICE advises testing for ovarian cancer in any woman aged 50 or over who has developed symptoms suggesting IBS in the past 12 months, because IBS rarely appears for the first time at that age. New IBS-type symptoms after 50 are a reason to see a GP, not a reason to start an IBS diet.
Food intolerance and coeliac disease
A food intolerance is a digestive problem, not an allergy: no immune reaction, no risk of anaphylaxis, and symptoms that depend on dose. Lactose intolerance is the most common, and is the norm rather than the exception in much of the world’s adult population. Fructose, sorbitol, mannitol and xylitol cause the same trouble by the same mechanism — poorly absorbed sugar reaching the colon and being fermented.
Coeliac disease is different and is not an intolerance at all. It is an autoimmune condition in which gluten damages the lining of the small intestine, and it affects around 1 in 100 people in the UK, many of whom are still undiagnosed. Bloating is one of its commonest symptoms, often alongside tiredness, iron deficiency, mouth ulcers, diarrhoea or unexplained weight loss. NICE recommends testing anyone with persistent unexplained abdominal or gut symptoms, and the test is a simple blood test — but only if you are still eating gluten. Coeliac UK advises gluten in more than one meal a day for at least six weeks beforehand.
Home intolerance tests: IgG food-sensitivity panels, hair analysis and applied kinesiology are not diagnostic tests for anything. They routinely flag foods you tolerate perfectly well, and the diets built from them cause more restriction and more misery than the original symptom. A structured elimination and reintroduction, ideally with a dietitian, is the only reliable way to identify a food trigger.
Reflux, indigestion and swallowed air
Upper abdominal bloating with belching, early fullness and a burning discomfort behind the breastbone is usually reflux or functional dyspepsia rather than a lower gut problem. Repeated belching in particular is often a learned cycle of swallowing air and bringing it straight back up, which feels like relieving pressure but adds to it.
If your bloating sits high up and comes with heartburn or regurgitation, our acid reflux and GORD page covers the mechanism and the treatment ladder, and these guides go deeper: indigestion vs heartburn vs acid reflux, foods to avoid, and hiatus hernia. Persistent nausea alongside bloating and early fullness has its own set of causes, covered on our nausea and vomiting page.
Hormonal and gynaecological causes
Cyclical bloating in the week before a period is common and normal: progesterone slows gut transit and encourages fluid retention, and both reverse once the period starts. It should track your cycle, and it should ease.
Bloating that does not track the cycle, or that comes with deep pelvic pain, pain during sex, heavy or painful periods, or pain on opening the bowels around a period, deserves a different conversation. Endometriosis is a frequent and frequently delayed diagnosis behind exactly this picture — see our endometriosis page — and fibroids can cause both visible distension and pressure symptoms. Bloating alongside a change in periods in your forties may be perimenopausal; our HRT page and period pain page cover the wider picture.
Persistent bloating in women: the ovarian cancer rule
This is the single most important section on this page. Ovarian cancer is diagnosed in around 7,700 women a year in the UK, and it is often found late — not because it is silent, but because its early symptoms are the same everyday symptoms almost everyone has occasionally. The difference is persistence and frequency.
See a GP and ask about testing if you are a woman — particularly if you are 50 or over — with any of these on a persistent or frequent basis, especially more than 12 times a month: persistent abdominal distension (“bloating”), feeling full quickly or losing your appetite, pelvic or abdominal pain, or needing to pass urine more urgently or more often. This is the exact test threshold NICE sets in guideline NG12.
What happens next is straightforward: a CA125 blood test, and if it is raised, an ultrasound scan of the abdomen and pelvis. NICE also advises testing when unexplained weight loss, fatigue or a change in bowel habit accompany these symptoms, and specifically recommends testing any woman over 50 whose IBS-like symptoms have started in the last 12 months. The great majority of women who are tested do not have ovarian cancer. The test exists because it is the only way to find the minority who do while it is still early.
How to make the appointment count: keep a simple diary for two to three weeks — date, whether you were bloated, whether it had settled by morning, and anything else that day. “Bloated on 19 of the last 21 days, never flat in the morning” is a far stronger piece of information than “I’ve been bloated a lot lately”, and it maps directly onto the threshold your GP is working to.
Medicines and other medical causes
Bloating that started when a medicine started is worth taking seriously as a cause. GLP-1 weight loss medicines such as tirzepatide and semaglutide slow stomach emptying by design, so fullness, wind, bloating and constipation are among their most common side effects, particularly after each dose increase — our weight management page covers what to expect. Opioid painkillers, iron tablets, some antidepressants and anticholinergic medicines all slow the gut too.
Less common medical causes include gastroparesis (delayed stomach emptying, classically in long-standing diabetes), small intestinal bacterial overgrowth, pelvic or abdominal masses, and ascites — fluid in the abdominal cavity from liver disease, heart failure or malignancy. Ascites causes steady, progressive distension that does not fluctuate with meals or settle overnight, and is usually accompanied by other signs such as ankle swelling or breathlessness. That combination needs prompt medical assessment.
Red flags — when to get seen
Call 999 or go to A&E for sudden severe abdominal pain, a rigid or very tender abdomen, vomiting blood or coffee-ground material, black tarry stools, or a distended abdomen with vomiting and no passage of wind or stool.
Same-day advice (contact your GP or call 111) for bloating with a fever, persistent vomiting, severe pain, an inability to pass urine, or a swollen abdomen that has come on rapidly over a day or two.
Book a GP appointment for any of the following:
- Bloating on most days for three weeks or more, or more than 12 times in a month
- Abdominal swelling that is present on waking and does not settle overnight
- Unexplained weight loss, or losing your appetite or feeling full very quickly
- Blood in the stool, rectal bleeding, or black stools
- A change in bowel habit lasting six weeks or more, particularly over 60
- Difficulty swallowing, persistent vomiting, or pain that wakes you at night
- Tiredness or breathlessness suggesting iron deficiency anaemia
- New IBS-type symptoms over the age of 50, or a family history of bowel or ovarian cancer
- Post-menopausal bleeding, or pelvic pain with bloating
How bloating is assessed
There is no single test for bloating. A clinician works through the possibilities in a fairly consistent order, and knowing the order makes the appointment more useful.
The history
Pattern over time, relationship to meals and to the menstrual cycle, whether it settles overnight, bowel habit, weight, appetite, medicines, and family history. This alone narrows it dramatically.
Examination
Abdominal examination looking for tenderness, masses, an enlarged liver or spleen and signs of fluid; a pelvic examination where the history points that way.
First-line blood tests
Full blood count for anaemia, coeliac serology (while still eating gluten), inflammatory markers, and thyroid, liver and kidney function. CA125 where the ovarian criteria are met.
Stool tests
Faecal calprotectin to separate inflammatory bowel disease from IBS, and a FIT test for hidden blood where bowel cancer needs excluding.
Imaging or endoscopy
Ultrasound of the abdomen and pelvis, and endoscopy or colonoscopy where red flags, abnormal tests or treatment failure make it necessary.
What actually helps
Once serious causes are off the table, most bloating improves with unglamorous measures applied consistently for a few weeks.
- Treat constipation first — more fluid, soluble fibre, and the right laxative if needed. Fixing this alone resolves a large share of bloating
- Eat more slowly and in smaller amounts, chew properly, and leave three hours between the last meal and bed
- Cut the obvious gas sources for two weeks — fizzy drinks, chewing gum, sugar-free sweets containing sorbitol or xylitol, drinking through straws
- Walk after meals. Physical activity measurably speeds gas transit and is one of the few interventions with consistent evidence
- Swap insoluble for soluble fibre — oats, ispaghula and linseed rather than bran — and increase it gradually
- Try enteric-coated peppermint oil for four weeks if bloating and cramping dominate
- Trial a probiotic for up to four weeks at the dose on the packet, and stop it if nothing has changed
- Consider a low FODMAP diet with a dietitian if IBS is confirmed — it is an elimination and reintroduction process, not a permanent diet
- Keep a two-week symptom diary before your appointment — it is the most useful thing you can bring
For cramping and spasm alongside bloating, antispasmodics such as mebeverine or hyoscine butylbromide are the usual pharmacy options, and simeticone is sometimes used for trapped wind. None of them treats the cause, and none is a reason to delay assessment if you have any of the red flags above.
What doesn’t help
Detox teas and cleanses
Most work as stimulant laxatives. They empty the bowel briefly, then leave it slower than before, and long-term use makes bloating worse.
IgG food-sensitivity tests
Not validated for diagnosing intolerance. They generate long exclusion lists and no reliable answers.
“Candida” and parasite cleanses
These are not recognised diagnoses in people with a normal immune system, and the protocols delay real assessment.
Going gluten-free before testing
The one genuinely harmful shortcut — it can make coeliac disease untestable for months.
Where to go next
Bloating is a symptom that belongs to several different conditions, so the useful next step depends on which picture fits you.
If bloating needs more than self-help
Anything on the red flag list above belongs with your GP. If your bloating fits the IBS picture and you want to discuss treatment, Access Doctor is a GPhC-registered pharmacy and our pharmacist independent prescribers can assess you online — our IBS page explains how that works.
IBS at Access Doctor →Frequently Asked Questions
Why am I so bloated all the time?
Most persistent bloating comes down to one of four things: what you eat and how quickly, constipation, a functional gut disorder such as IBS, or a food intolerance. Constipation is the most common treatable cause and the easiest to miss, because you can open your bowels every day and still be incompletely emptying. Bloating that has been present for years, comes and goes, and is worse in the evening than on waking is usually functional. Bloating that is new, constant, and getting worse is the pattern that needs a doctor.
What is the difference between bloating and abdominal distension?
Bloating is the sensation — feeling full, tight or swollen. Distension is the measurable fact of the abdomen getting bigger, so that clothes tighten and the waistband moves. The two often go together but not always: you can feel bloated with no visible change, and some people distend visibly without much discomfort. The distinction matters because visible distension that does not settle overnight is more likely to have a physical cause worth investigating.
When is bloating a sign of something serious?
The pattern matters more than the severity. Bloating that is persistent rather than intermittent, that is new in someone over 50, that does not settle overnight, or that comes with unexplained weight loss, blood in the stool, difficulty swallowing, persistent vomiting or a change in bowel habit should be assessed rather than managed at home. Sudden severe abdominal pain, a rigid or very tender abdomen, vomiting blood, black tarry stools, or being unable to pass wind or stool at all are emergencies — call 999.
Can bloating be a sign of ovarian cancer?
It can, which is why NICE sets a specific rule. Any woman — particularly if she is 50 or over — who has persistent abdominal distension, feeling full quickly or loss of appetite, pelvic or abdominal pain, or needing to pass urine more urgently or frequently, on a persistent or frequent basis and especially more than 12 times a month, should be offered tests in primary care. That means a CA125 blood test, followed by an ultrasound of the abdomen and pelvis if it is raised. Most women tested will not have ovarian cancer, but the test is how the minority who do get found early.
How long should bloating last before I see a doctor?
As a rule of thumb, bloating that has been present on most days for three weeks or more, or that happens more than 12 times in a month, has stopped being an everyday nuisance and should be looked at — sooner if you are over 50, have a family history of bowel or ovarian cancer, or have any red flag symptoms. Bloating that clearly tracks your diet, your menstrual cycle or a period of constipation, and settles in between, is far less concerning.
Is bloating a symptom of IBS?
Yes — bloating is one of the core features NICE lists in the diagnosis of irritable bowel syndrome, alongside abdominal pain that is relieved by opening your bowels or associated with a change in stool frequency or form. In IBS the bloating typically builds through the day, is worse after meals, and is better on waking. IBS is a positive diagnosis rather than a leftover one, but it is only made once the red flags have been excluded and basic tests such as coeliac serology are normal.
Should I cut out gluten to see if it helps?
Not before you are tested. Coeliac disease affects around 1 in 100 people and bloating is one of its most common symptoms, but the blood test and the biopsy both work by measuring your response to gluten. If you have already stopped eating it, the tests can come back falsely normal. Coeliac UK advises eating gluten in more than one meal a day for at least six weeks before testing. So ask for the test first, keep eating gluten until it is done, and change your diet afterwards.
Do probiotics, peppermint oil or simeticone actually work for bloating?
Peppermint oil has the best evidence of the three for bloating and abdominal pain in IBS, and is worth a four-week trial. Simeticone breaks up gas bubbles and helps some people with wind, though the evidence is thin. Probiotics are worth trying for up to four weeks at the dose on the packet, but stop if nothing changes — NICE takes the view that they help some people and not others, and there is no reliable way to predict who. None of the three is a substitute for treating constipation if constipation is the real problem.
Why do I get bloated around my period?
Cyclical bloating in the days before a period is common and is driven by the hormonal changes of the luteal phase, which slow gut transit and encourage fluid retention. It should ease once the period starts. Bloating that is severe, that lasts the whole month rather than tracking the cycle, or that comes with deep pelvic pain, pain during sex or heavy periods is a different picture and worth investigating — endometriosis and fibroids both cause bloating and both are commonly missed.
Can weight loss injections cause bloating?
Yes. GLP-1 medicines such as tirzepatide and semaglutide work partly by slowing stomach emptying, so bloating, fullness, wind and constipation are among the most common side effects, particularly in the first weeks and after each dose increase. It usually settles with smaller meals, slower eating and treating any constipation. Bloating with severe or persistent abdominal pain on a GLP-1 is different and should be reported to your prescriber promptly.
References
- National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12). nice.org.uk
- National Institute for Health and Care Excellence. Ovarian cancer: recognition and initial management (CG122). nice.org.uk
- National Institute for Health and Care Excellence. Irritable bowel syndrome in adults: diagnosis and management (CG61). nice.org.uk
- National Institute for Health and Care Excellence. Coeliac disease: recognition, assessment and management (NG20). nice.org.uk
- NHS. Bloating. nhs.uk
- Coeliac UK. Getting diagnosed. coeliac.org.uk
- Cancer Research UK. Ovarian cancer incidence statistics. cancerresearchuk.org
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Bloating has many causes and only a clinician who can assess you is able to say which applies to you. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
