IBS Pain on the Left Side: Causes and Red Flags

Yes, IBS can cause pain on the left side, and for a lot of people it is the signature spot: low on the left above the hip bone, or tucked up under the left ribs. Both places are where the colon bends or holds stool, so gas and stool collect there and strong contractions pass through, and in a gut with sensitive nerves that can hurt. But the side your pain is on is a weaker clue than most pages suggest. The colon is poor at telling your brain where a problem actually is, and several things that are not IBS also live on the left. This article explains what is on your left side, why IBS pain gathers there, what the research does and does not show about "splenic flexure syndrome", what helps, and the specific features that mean left-sided pain needs a doctor rather than a hot water bottle.

This post is about location. How to describe pain in words, rate it out of ten and explain it in an appointment is covered in our guide on how to describe stomach pain to a doctor, and we link there rather than repeat it. Where we say we "could not find" a study, that reflects our searching of PubMed and Europe PMC for this article, not proof that none exists.

The short answer: yes, and here is why the left side

IBS pain on the left side is common, and it is almost always the colon. The large bowel runs up the right side of your abdomen, across the top, down the left side, and then makes an S-shaped curve low on the left before reaching the rectum. Two features of that route matter for pain.

First, the colon turns a sharp corner under your left ribs. This bend, the splenic flexure, is a corner that gas and stool moving along the colon have to get round. Second, the last part of the colon, the sigmoid colon, curves low on the left side of your pelvis. This is where stool waits before it is passed, and it is a segment that contracts strongly.

So in IBS, where the nerves of the gut report normal stretching and squeezing as pain, the left side is where a lot of that stretching and squeezing happens. The largest IBS community on Reddit has a thread asking whether everyone has constant lower left pain, with more than 400 replies, and the top answer is essentially relief that someone else has it too (r/ibs thread). Many people in that thread describe pain that is worse when constipated, eases after passing gas or stool, and has survived normal scans and a normal colonoscopy. That pattern fits IBS well.

But it is worth holding two things at once. Left-sided pain fits IBS. Left-sided pain is not proof of IBS. The rest of this article is about both halves of that sentence.

What is actually on your left side

Before thinking about IBS, it helps to know what else lives on the left, because the list of neighbours is what decides which extra symptoms matter. The table below is a rough map, not a diagnostic tool. Organs overlap, people vary, and pain from inside the abdomen is often felt away from its source.

You will notice the colon appears in every row. That is part of why IBS can feel like it is everywhere on the left, and part of why a doctor will ask about the other features in the right-hand column rather than relying on where you point.

The surprising part: your colon is bad at telling you where it hurts

Gut pain is notoriously hard to locate. The best direct evidence comes from two balloon studies, and they are worth knowing in detail because they change how you should read your own pain.

In 1973, a researcher inflated a balloon 35 cm inside the sigmoid colon, the S-shaped bend low on the left, in 67 people with IBS and 16 controls. At a volume of 60 ml, 55% of the people with IBS felt pain compared with 6% of controls, even though the estimated tension in the bowel wall was normal in the IBS group (Ritchie 1973). That is the core finding behind "visceral hypersensitivity": the same stretch, felt very differently. But look at where the pain was felt. The balloon was in the left-sided colon every time, yet the pain was felt low in the middle of the abdomen in 40% of people, in one or both lower sides in 31%, in the rectum in 21%, and in the back or elsewhere in 8%. Fewer than a third felt it at the sides at all, and the paper does not split that into left and right.

In 1980, another team went further. During colonoscopy they inflated a balloon at several points throughout the colon in 48 people with painful IBS and in nine people who had come in with rectal bleeding but had no pain (Swarbrick 1980). In the comparison group, the colon's pain was felt mainly in the central, lower and left abdomen. In the people with IBS, it could be felt in any part of the abdomen. Stretching the ascending and transverse colon, the right side and the top, often produced pain on the right or in the upper abdomen. In 29 of the 48 people with IBS, the balloon reproduced their usual pain in both feel and location. And some pain was referred to sites outside the abdomen altogether, which the authors described as previously undescribed. Their conclusion was that wider recognition of where colonic pain can be felt could prevent unnecessary investigations, including surgery.

Two practical lessons follow. First, the spot where you feel pain is a rough pointer to the bowel, not a map of it. Left-sided pain often comes from a left-sided part of the colon, but pain from any one part of the colon is not reliably felt over that part. Second, this cuts both ways. "It's on the left, so it must be my colon" is not safe reasoning either, which is why the features in the red-flag sections below matter more than the side.

Is the lower left really the most common IBS pain site?

Several pages ranking for this search say IBS pain is felt "most commonly" on the lower left. We looked for the study behind that and could not find one. We found no survey or cohort that counted where people with IBS feel their pain and reported the left lower area as the commonest. The British Society of Gastroenterology guideline simply reminds clinicians that "the location of pain can be in the upper or lower abdomen" and that what matters is the link between pain and bowel habit (Vasant 2021).

The left-sided claim may well be true. The anatomy makes it plausible, and the size of the Reddit thread above suggests plenty of people recognise it. But it appears to be clinical folklore rather than a measured figure, and a page that states it as fact without a source is guessing. What location can and cannot tell a doctor is covered in the location section of our pain description guide.

Lower left: the sigmoid colon

Low left pain in IBS is most often the sigmoid colon at work. This is the S-shaped final stretch of colon that sits in the left side of your pelvis, and it is where stool is stored before you feel the urge to go.

Why it hurts. Three things can happen here. Stool can sit and stretch the bowel, which is why many people with constipation-predominant IBS describe a heavy, full ache on the lower left that eases after a bowel movement. Gas can be trapped behind stool. And the colon can produce powerful sweeping contractions that push contents along. In a small study of 10 people with IBS who had pain and diarrhoea, recordings from the transverse, descending and sigmoid colon showed more of these high-amplitude contractions than in 10 healthy volunteers, and abdominal pain coincided with more than 90% of them (Chey 2001). The authors suggested these powerful contractions are one of the causes of IBS pain. That study was in diarrhoea-predominant IBS only, and it is small, but it shows that pain can track the colon's own movements in real time.

Why it varies with your subtype. In IBS with constipation, the ache is often more constant and tied to how long it has been since you last went. In IBS with diarrhoea, many people describe it as crampy and coming just before an urgent bowel movement. Your subtype is set by your stool pattern, not your pain, and the rules for that are covered in the difference between IBS-D and IBS-C. But knowing your subtype helps make sense of which kind of left-sided pain you get.

Relief after a bowel movement is less reliable than you might think. Pain eased by opening your bowels is part of the classic IBS picture, and it is often why people suspect the sigmoid colon. But in a Swedish study where 63 people with IBS recorded every pain episode for six weeks, 38 of the 59 who recorded pain (64%) said at the start that a bowel movement relieved their pain, yet on average only 10% of each person's recorded pain episodes were actually relieved by one (Ragnarsson 1998). So if your lower left pain does not reliably lift after the toilet, that does not mean it is not IBS.

A note on that study's arithmetic, since we checked it: the abstract reports 38 people as 64% and 29 people as 49%, which only works if the denominator is the 59 people who recorded any pain, not the 63 who finished. We have used 59.

Diverticular disease: the left-side neighbour with an overlap

Diverticula are small pouches in the colon wall. When one becomes inflamed, that is diverticulitis, and its most common presenting symptom is pain in the lower left of the abdomen, usually coming on acutely or over a few days (Peery 2021).

The relationship with IBS is more tangled than "one or the other". In a study of 1,009 people having colonoscopy at seven centres in Japan, people with diverticula on the left side of the colon, or on both sides, were more likely to also meet the criteria for IBS (odds ratio 3.1 for left-sided disease, 95% CI 1.4 to 7.1), while right-sided diverticula showed no link (Yamada 2014). That was a single snapshot, so it shows an association, not that one causes the other. It is also worth knowing that in that Japanese group right-sided diverticula were much commoner (21.6% of people) than left-sided ones (6.6%), so the findings may not transfer neatly to other populations.

Diverticulitis may also leave IBS behind. A US veterans' study compared 1,102 people who had had diverticulitis with 1,102 matched people without diverticula, excluding anyone with a prior IBS or mood diagnosis. Over an average of 6.3 years, the diverticulitis group were 4.7 times more likely to be diagnosed with IBS later, with a wide confidence interval of 1.6 to 14.0 (Cohen 2013). The authors proposed the term post-diverticulitis IBS, by analogy with IBS after a gut infection. That paper discloses that three of its authors were employed by Shire Pharmaceuticals and another had advised and received research support from several drug companies. The American Gastroenterological Association's expert review takes a similar line: ongoing symptoms are common after acute diverticulitis, with periodic abdominal pain reported by about 45% of people a year later in one trial, and visceral hypersensitivity is the likely cause in most cases (Peery 2021). The same review says ongoing inflammation, a stricture, a fistula and other diagnoses should be excluded with imaging and a colonoscopy first.

So if you have had diverticulitis, a later grumbling lower left pain may be IBS-type sensitivity. But how to tell the two apart in the moment is covered in the red-flag section below, because that distinction matters.

Under the left ribs: the splenic flexure

Pain or pressure under the left ribs is the other classic IBS location, and it is the one people search for most anxiously. It usually comes from the splenic flexure, the sharp bend where the colon running across the top of your abdomen turns down the left side. It is named after the spleen, which sits nearby.

People describe this pain in very consistent ways. In Reddit threads about it, the recurring descriptions are a trapped bubble or a fist-sized pressure under the left ribs, a feeling of not being able to take a full breath, gurgling or sloshing in the same spot, pain that is worse when bending forward or wearing a tight waistband, and pain that sometimes runs round to the left mid-back (r/ibs thread, r/ibs thread). Another thread, from someone with years of constant pressure under the left rib despite a normal colonoscopy, endoscopy, CT and bloodwork, drew replies from people who had been told it is where the bowel makes a big turn, and also from people whose similar pain turned out to be a kidney stone, pancreatitis, a gynaecological problem or reflux (r/ibs thread). Both kinds of reply are useful. The pattern is common, and it is not always the colon.

Is "splenic flexure syndrome" a real diagnosis?

It is a real term with a long history, but a thin evidence base. Splenic flexure syndrome appears in article titles indexed in Europe PMC from at least the 1950s, including a 1965 case report titled exactly that (Shafar 1965). We could only obtain that paper as a scanned image without readable text, so we cite it here only to date the term, not for anything it says. We found no modern trial that defines splenic flexure syndrome with agreed criteria or tests a treatment for it.

The most informative study we could read is a Russian one from 2008 that compared 82 people whose splenic flexure sat unusually high with 76 people with IBS and 19 controls (Osipenko 2008). According to its abstract, some of the people with a high splenic flexure had left-sided pain, that pain matched the clinical criteria for IBS, and it came with a lower pain threshold to balloon stretching, the same hypersensitivity seen in IBS. The authors concluded that splenic flexure syndrome can be considered a variant of IBS arising in people with this anatomy, and that it should be treated on IBS principles. We read only the English abstract of a Russian-language paper, so treat that as the authors' summary rather than something we could check in full.

That fits the wider picture. Splenic flexure syndrome is best understood as a description of where IBS-type gas pain is being felt, not as a separate disease with its own treatment. That matters, because some of the advice circulating online treats it as a structural problem with a single fix.

Why gas hurts there: it is distribution, not volume

Many people assume left upper pain means they make too much gas. The research points elsewhere.

• In 1975, researchers measured the total gas in the intestines of 12 people with chronic complaints of excess gas and 10 controls. The volumes were not different (176 ml versus 199 ml on average). What differed was handling: six people who developed severe pain during the study cleared the gas much more slowly, about 40 minutes versus 22 minutes in controls, and gas tended to reflux back into the stomach in those who felt pain (Lasser 1975).
• In 2001, a Barcelona group infused gas into the small intestine of 20 people with IBS and 20 healthy controls. After two hours, 18 of the 20 people with IBS had developed gas retention, increased symptoms or abdominal distension, compared with 4 of the 20 controls (Serra 2001).
• In 2003, the same group showed in 14 healthy volunteers, not people with IBS, that the same amount of retained gas, about 720 ml, caused much more discomfort when it was held higher up in the gut than when it was held low down near the rectum, even though belly swelling was the same (Harder 2003). Their conclusion was that the volume of gas sets how much you swell, but where the gas sits sets how much it hurts.

Put together, that is a reasonable explanation for splenic flexure pain in IBS, though nobody has measured it at the flexure specifically. Gas moving along the colon reaches a high, tight bend. In a gut that clears gas slowly and feels stretch more keenly, a pocket that sits there can be felt as sharp or heavy pain under the ribs, and it eases when the gas moves on, which is why so many people describe relief after a gurgle or after passing wind. If visible swelling is a big part of your picture, our post on IBS bloating that makes you look pregnant explains the separate diaphragm mechanism behind distension.

Can the shape of your colon matter?

Some people are told during a colonoscopy that their colon is long or loopy, or that it was hard to get the scope round the splenic flexure. A long, looped colon is called a redundant colon, or dolichocolon. Researchers writing in 2024 describe it as an anatomical variant "thought to be associated with constipation, abdominal pain, and distention", and one of its definitions on CT is redundant loops at the hepatic or splenic flexure (Dilmaghani 2024). Note the wording "thought to be". We could only read the introduction of that research letter, so we cannot tell you what it found about transit, and we found no good evidence that a redundant colon on its own explains a particular person's pain. If you have been told this, it is a reasonable question for your gastroenterologist, not a diagnosis to give yourself.

Left side and back: bowel or kidney?

Pain from the colon can be felt in the back, and the 1980 balloon study found colonic pain referred to several places outside the abdomen (Swarbrick 1980). People with splenic flexure pain often describe it wrapping round to the left mid-back. So IBS can contribute to left-sided back pain.

But the left kidney sits directly behind the descending colon, and it is the usual suspect for pain in the left flank. Kidney stones typically cause renal colic, severe pain that comes in waves, and less often a duller loin ache, sometimes with visible blood in the urine, vomiting and occasionally fever (Khan 2016). In one of the Reddit threads, a commenter described a year of dull left-sided ache that everyone attributed to their bowel until an X-ray found a large kidney stone (r/ibs thread). That is one story, not evidence, but it illustrates the trap.

The practical differences worth noticing:

• IBS-type back pain tends to rise and fall with meals, gas and bowel movements, and often comes with front-of-belly pain too.
• Kidney pain tends to have nothing to do with eating or the toilet, can make it impossible to get comfortable in any position, and may come with changes in your urine.
• Muscle and spine pain changes with posture, movement and twisting, and is often tender to press.

If your back pain does not fit the first pattern, mention it to a doctor as a separate symptom rather than filing it under IBS.

Why the pain starts when you eat

Eating switches on the colon. After a meal, the colon's activity rises as part of a normal reflex, which is why many people need the toilet soon after eating, a pattern explained in why you have to poop right after eating. In IBS, that normal surge can be painful.

The six-week Swedish diary study gives the clearest numbers. At the start, 49% of the people who recorded pain said their pain got worse after eating. But when they actually logged each episode, on average half of each person's pain episodes worsened after meals, a much more consistent link than the one with bowel movements (Ragnarsson 1998). The authors suggested that pain worsening after meals should be part of the clinical definition of IBS.

For left-sided pain, that means a meal can set off a contraction or a pocket of gas in the sigmoid colon or at the splenic flexure, and you feel it there. The timing of reactions to food is covered in how long after eating IBS flares up, including why a reaction an hour after lunch may not be about lunch at all.

There is one exception worth knowing. Pain that reliably starts 15 to 30 minutes after every meal, together with weight loss and a growing fear of eating, is a recognised pattern of reduced blood supply to the gut, seen mostly in people over 60 (Ahmed 2021). That pain is usually in the upper or middle abdomen rather than the left, and it is rare, but it is a reason not to assume all meal-linked pain is IBS, especially if you are older.

Did my colonoscopy check this area?

If you had a complete colonoscopy, yes: it looks at the lining of the whole colon, including the sigmoid colon, the descending colon and the splenic flexure on the left. That rules out a lot. Inflammation from colitis, a polyp or tumour on the lining, and the visible changes of diverticular disease would usually be seen.

What a colonoscopy cannot see is anything outside the bowel. The kidneys, the ovaries and fallopian tubes, the pancreas, the spleen and the muscles and nerves of the abdominal wall are all outside its view. It is also a snapshot: it cannot show how your colon moves or how it handles gas. And it is not the test for every left-sided condition. For acute diverticulitis, for example, the diagnosis is made with a CT scan, which the AGA review describes as highly accurate, with sensitivity and specificity of about 95% (Peery 2021).

So a normal colonoscopy should genuinely reassure you about the lining of your colon. It should not end the conversation if your pain has features that point elsewhere, such as urinary symptoms, pain linked to your cycle, pain that is tender to press in one spot, or pain that does not change with eating or bowel habit. One kind of pain worth knowing about here comes from the abdominal wall rather than the gut. Pain you can cover with a fingertip that is tender to touch can come from a trapped nerve or muscle, and there is a simple bedside test for it; our pain description guide explains how to raise it. And if left-sided pain changes with your menstrual cycle, endometriosis is worth asking about, which why IBS gets worse on your period covers in detail.

If repeated normal tests have not quietened your worry, and the pain keeps sending you back to search results, that is a pattern of its own. IBS and health anxiety explains why reassurance can wear off and what helps. Some people also notice their left-sided pain is worse for a while after the procedure itself; IBS flares after a colonoscopy covers that.

What helps, and how good the evidence is for each

Nothing has been tested specifically for left-sided IBS pain. Every option below was studied for IBS pain in general, or for related problems, and we say which.

Antispasmodics

Certain antispasmodic medicines, which relax gut muscle, are listed in the British Society of Gastroenterology guideline as possibly effective for global symptoms and abdominal pain in IBS, with the caveat that side effects, most notably dry mouth, visual disturbance and dizziness, were more common than with placebo (Vasant 2021). They are a reasonable thing to ask a GP or pharmacist about if your pain feels crampy and spasm-like. Which one, and whether it suits you, is a conversation for them.

Peppermint oil

Peppermint oil is thought to relax gut muscle. A meta-analysis of 8 trials with 823 people, summarised in the BSG guideline, found it more effective than placebo for global symptoms or abdominal pain, though the guideline flags low study quality and says the results apply only to the specific formulations tested (Vasant 2021).

The largest single trial is instructive for left-sided pain. A Dutch trial of 190 people with IBS tested two capsule types: a standard one that releases peppermint oil in the small intestine, and a newer one designed to release it further along, at the end of the small bowel and into the colon (Weerts 2020). The colon-targeted version is the one you might expect to work best for colonic pain on the left. It did not. On the trial's main measure, a 30% drop in worst daily pain in at least four of eight weeks, 41.3% responded on the colon-release capsule, 46.8% on the small-intestine capsule and 34.4% on placebo, and neither difference was statistically significant. Subtracting placebo, that is about 7 and 12 percentage points respectively, and the trial was not able to show either was real. The small-intestine capsule did improve pain, discomfort and overall IBS severity on secondary measures, and the authors concluded the colon-targeted capsule should not be developed further. Side effects were mild but more common with both peppermint capsules. Europe PMC lists the Dutch public research funder ZonMw among its grants, alongside several drug companies whose role we could not establish from the abstract.

The honest reading: peppermint oil may help some people's IBS pain, the effect is modest, and delivering it straight to the colon did not make it better.

Heat

Heat is the remedy people in the Reddit threads mention most often, from hot water bottles to heat pads worn for hours (r/ibs thread). We could find no trial of heat for IBS pain. It is cheap and low risk if you avoid burns, so there is no reason not to use it if it helps you, but we cannot point you to evidence that it changes anything in the bowel. Take care with long contact on the same patch of skin, and be cautious if you have reduced sensation.

Abdominal massage

Many people with left-sided pain describe pressing or massaging along the colon to move gas on, and some find it works within minutes. The best trial we found was not in IBS. In a Swedish trial of 60 people with constipation, adding abdominal massage to their usual laxatives for eight weeks reduced gastrointestinal symptoms, including an abdominal pain score, and increased bowel movements compared with laxatives alone (Lämås 2009). The massage did not reduce laxative use. Studies specifically in IBS that we found were in rats. So for constipation-type lower left pain, massage has some support. For IBS as a whole, it is an untested comfort measure, and pressing hard on a tender spot that is getting worse is a reason to stop and get checked rather than press harder.

Movement and position

Gas moves through the gut more easily when you are upright and moving than when you are lying still, and some people find lying on one side or gentle walking shifts a trapped pocket. The evidence for posture and exercise on gas clearance, and its limits, is covered in our post on loud stomach noises with IBS and in exercise and IBS flare-ups, so we will not repeat it here.

Diet and the longer game

If left-sided pain is driven by gas and stool, then what you eat and how regular your bowels are will shape it. A structured low FODMAP diet, done for a short period with a dietitian and followed by reintroduction to find your personal triggers, is a recognised approach in IBS; what FODMAP stands for explains the groups and why it is not meant to be permanent. Plenty of people in the community threads say a strict version made them miserable, which is exactly why the reintroduction stage and professional support matter. Gut-directed psychological treatments target the sensitivity side of the problem directly; whether gut-directed hypnotherapy works for IBS covers that evidence.

When left-sided pain is not IBS

This is the most important section. IBS is diagnosed on its pattern, with simple tests to exclude other conditions, and no symptom of IBS is unique to it. The BSG guideline recommends that anyone first presenting with IBS-type symptoms has a full blood count, an inflammation marker, coeliac blood tests and, if under 45 with diarrhoea, a faecal calprotectin test to look for inflammatory bowel disease, and that local guidance on bowel and ovarian cancer is followed where it applies (Vasant 2021). If you have never had those basics, start there.

Beyond that, these are the conditions on the left side that can be mistaken for IBS, and the features that tend to separate them.

A few of these deserve a sentence more.

Ischaemic colitis likes the left side and the splenic flexure. The splenic flexure sits at a "watershed" where two arterial supplies meet with few connections between them, which makes it vulnerable when blood flow drops. In a 2021 review, the left colon was involved in about two-thirds of cases, with the splenic flexure, descending colon and sigmoid colon the commonest sites (Ahmed 2021). Most cases are in people over 60, but the same review lists IBS among the rarer settings in which it occurs in younger people, along with long-distance running, substance misuse and medical procedures. The tell is the sequence: sudden cramping, urgency, then blood within a day. That is not an IBS flare.

Pancreatitis pain has a different character. The American College of Gastroenterology guideline describes typical pancreatitis pain as epigastric or left upper quadrant, usually constant, with radiation to the back, chest or flanks, and says pain that is dull, colicky or low in the abdomen is not consistent with it (Tenner 2024). Severe, constant upper left pain boring through to your back needs urgent assessment, not a heat pad.

Pain alone is a weak signal for cancer, but not a zero one. In a systematic review of primary care studies, abdominal pain on its own had a pooled positive predictive value for colorectal cancer of 3.3%, with a very wide confidence interval of 0.7% to 16%, a lower point estimate than rectal bleeding in people aged 50 and over (8.1%) or anaemia (9.7%) (Astin 2011). That is a primary care population, not people with long-standing IBS, so it is not your personal risk. The colorectal cancer referral criteria listed in the BSG guideline include being 40 or over with unexplained weight loss and abdominal pain, and being 60 or over with a change in bowel habit or iron deficiency anaemia; rectal bleeding with abdominal pain under 50 is listed as a probable referral criterion (Vasant 2021).

Bloody diarrhoea and urgency suggest inflammation, not IBS. Ulcerative colitis is described by how far up the colon it reaches, and one recognised pattern, left-sided colitis, runs from the rectum as far as the splenic flexure (Lamb 2019), so it can produce left-sided cramping. If you have blood, urgency, or symptoms that wake you at night, ask about a calprotectin test; high calprotectin but no symptoms explains what the result means.

A worked example: two weeks of logging left-sided pain

This example is invented to show the method. It is not a real person and not medical advice.

Sam, 34, has IBS with constipation and a pain under the left ribs that has been "there most days" for a year. A colonoscopy two years ago was normal. Sam's GP asks whether it is always the same, and Sam does not know. So for two weeks Sam logs four things each time the pain shows up: where exactly (pointing with a finger, upper left or lower left), what it feels like, what happened in the two hours before (meal, bowel movement, sitting slumped, stress), and what ended it.

At the end of 14 days the log shows:

• 19 episodes of upper left pain. 15 started within two hours of a large meal or a fizzy drink. 13 eased after passing wind or a gurgle. None came with fever, vomiting or urinary symptoms.
• 6 episodes of lower left ache, all on days with no bowel movement, all easing after one.
• 1 episode that did not fit: a dull ache in the left flank that lasted most of a day, had nothing to do with food or the toilet, and came with darker urine.

That log changes the conversation. Most of Sam's pain behaves like IBS: it tracks meals, gas and bowel habit, it lives where the colon bends and stores stool, and it moves on when the gas does. That is reassuring and points towards IBS-type management: regular bowels, meal size, and possibly an antispasmodic or peppermint oil. The single episode in the flank is the one to raise separately, because it behaved differently, and a urine test is cheap. Sam goes in with "most of my left-sided pain does this, and once it did something different", which is exactly what a clinician needs.

The pattern matters more than any single episode. If you want structure for this, how to keep a food diary for IBS covers the logging mechanics. If you use an app, Clairop lets you log a symptom in seconds when it happens, tests foods against delayed reaction windows, and produces a one-page summary for your appointment.

Myths about left-sided IBS pain

"Left-sided pain means it's definitely my colon." Usually it is, in IBS. But the left kidney, ovary, pancreas and spleen are all nearby, and the balloon studies show the colon's own pain wanders. Use the accompanying features, not the side, to decide.

"Right-sided pain is the dangerous side, left is safe." The appendix is on the right, so right lower pain gets the attention. But diverticulitis, ischaemic colitis and ectopic pregnancy all commonly cause left-sided pain. Neither side is safe or dangerous in itself.

"Splenic flexure syndrome is a separate disease that needs its own treatment." The term is decades old, there are no agreed diagnostic criteria, and the most direct study we found concluded it behaves like a variant of IBS and should be managed the same way (Osipenko 2008).

"I have too much gas." Most people who feel gassy have normal amounts of gas; the problem is slower clearance and greater sensitivity, and where the gas sits (Lasser 1975, Serra 2001).

"If a bowel movement doesn't relieve it, it can't be IBS." In a six-week diary study, a bowel movement relieved only about 10% of recorded pain episodes on average, even though most people believed it usually helped (Ragnarsson 1998).

"My colonoscopy was clear, so nothing else needs checking." A clear colonoscopy rules out a lot inside the colon. It does not look at the kidneys, ovaries, pancreas or abdominal wall.

"Colon-targeted peppermint capsules work better for colon pain." In the largest trial, the colon-release capsule did not beat placebo on its main measure, and the authors concluded it was not worth developing further (Weerts 2020).

When to see a doctor promptly

See a doctor promptly, rather than waiting it out, if your left-sided pain is new or has changed character, or comes with:

• blood in your stool, or black stools
• unexplained weight loss
• fever, chills or night sweats
• pain or diarrhoea that wakes you from sleep
• vomiting, or difficulty eating because of pain
• symptoms that started after the age of 50
• a family history of bowel cancer or inflammatory bowel disease
• a lump you can feel in your abdomen
• urinary symptoms, or pain that is clearly linked to your periods
• pain that is constant and never varies with eating, gas or bowel movements

If you already have an IBS diagnosis, the most useful thing you can say to a clinician is whether this pain is your usual pain or something different. Our guide on whether to see a gastroenterologist for IBS covers when a specialist referral makes sense, and the urgent signs in the warning box above always come first.

The honest bottom line

IBS pain on the left side is real, common and usually explained by anatomy: the colon bends under your left ribs and stores stool low on your left, and a sensitive gut feels gas and contractions in both places. Splenic flexure syndrome is an old name for the upper version of that pattern, not a separate disease. But the colon is a poor reporter of where pain comes from, nobody appears to have measured how often IBS pain is on the left, and several conditions that are not IBS live on the same side. So the side your pain is on should reassure you less, and the company it keeps should guide you more. Pain that moves with meals, gas and bowel habit, and has done so for months, fits IBS. Pain with fever, bleeding, weight loss, a sudden start or a fixed, unchanging character needs a doctor, whatever side it is on.