Can IBS Cause Fever and Chills?

Irritable bowel syndrome does not cause fever or chills. In fact, fever is classified as an “alarm symptom” in the diagnostic criteria used by gastroenterologists, meaning its presence should raise suspicion that something other than IBS is responsible for your symptoms. That said, the relationship between IBS, the immune system, and body temperature is more layered than a simple no, and several conditions that travel alongside or masquerade as IBS can produce fevers worth investigating.

Why Fever Is a Red Flag, Not a Symptom

The diagnostic frameworks that gastroenterologists use to identify IBS explicitly treat fever as a warning sign that a different disease may be at play. In the Rome IV criteria, which are the current standard for diagnosing functional gut disorders, fever appears on the list of alarm symptoms alongside rectal bleeding, unintended weight loss, anemia, and a family history of inflammatory bowel disease or colorectal cancer.¹ Earlier diagnostic frameworks took the same approach: the Rome III criteria also flagged fever as a “red flag” warranting further evaluation in patients who otherwise met the symptom profile for IBS.²

The logic is straightforward. IBS is a disorder of gut-brain interaction, characterized by abdominal pain tied to changes in bowel habits. It does not produce the kind of systemic inflammatory response that drives a true fever. When someone who has been diagnosed with IBS starts running a temperature, the guidelines say to look harder for an organic cause, not to chalk it up to the IBS itself. If you have IBS and you develop a fever, it deserves its own explanation.

The Low-Grade Inflammation That Does Not Quite Get There

One reason this question comes up so often is that IBS is not entirely free of immune activity. Research over the past two decades has shown that many IBS patients have subtle immune changes in their gut lining, sometimes called microinflammation. This involves increased numbers of certain immune cells in the colon’s mucosa and shifts in the balance of pro-inflammatory and anti-inflammatory signaling molecules. But the key qualifier is that these changes are too mild to show up on standard blood tests or produce visible inflammation under a microscope.³

Studies have found that patients with diarrhea-predominant IBS tend to have higher circulating levels of inflammatory markers like IL-6 and TNF-α compared to healthy people.⁴ These are the same molecules your body ramps up during an infection, and in high enough concentrations they can trigger fever. But in IBS, the elevations are modest. Think of it as background noise in the immune system rather than a full alarm. The levels are high enough to interest researchers studying IBS mechanisms but nowhere near the territory that would make you feel feverish or send your CRP soaring.

This distinction matters because it helps explain a common experience: feeling “off” or mildly unwell during an IBS flare without actually having a measurable fever. Some people describe a sensation of warmth, flushing, or mild chills during bad episodes, which may relate to the autonomic nervous system changes seen in IBS rather than to a true rise in core body temperature.

Post-Infectious IBS and the Fever That Started It All

A significant subset of IBS cases begin after a bout of acute gastroenteritis. This is called post-infectious IBS, and it accounts for a meaningful fraction of new diagnoses. The pattern is familiar: you catch a stomach bug, you recover from the acute illness, but your gut never quite returns to normal. Months later you still have cramping, bloating, and altered bowel habits that meet the criteria for IBS.⁵

In a large survey of people with post-infectious IBS, about half reported fever during the original triggering infection.⁶ A meta-analysis went further and identified prolonged fever during the initial gastroenteritis as an actual risk factor for later developing post-infectious IBS.⁷ In other words, the worse the fever during the original infection, the more likely your gut is to be left with lasting functional changes.

This creates a confusing timeline for patients. You had a stomach infection with a high fever. The infection resolved, but the gut symptoms persisted and eventually got labeled IBS. Now every time your symptoms flare, you associate it with the original illness and wonder whether the fever is coming back too. The important distinction is that the fever belonged to the infection, not to the IBS that followed. If fever returns months or years later during a flare, that is a new event that needs its own investigation.

Conditions That Look Like IBS but Do Cause Fever

Several organic diseases can produce symptoms that closely overlap with IBS. Some of these conditions do cause fever, and because their day-to-day symptom profile can be almost indistinguishable from IBS, they sometimes go undiagnosed for years.

Inflammatory bowel disease, which includes Crohn’s disease and ulcerative colitis, is the most important one. IBD involves genuine, visible inflammation of the gut lining and can produce fever, fatigue, weight loss, and bloody stools alongside the cramping and diarrhea that also define IBS. The overlap is close enough that distinguishing between the two has been a persistent clinical challenge. One of the clearest ways to separate them is through inflammatory markers. In one study, the median fecal calprotectin level in IBS patients was nearly identical to that of healthy controls, while patients with ulcerative colitis had levels roughly 90 times higher. A calprotectin cutoff of about 110 micrograms per gram distinguished IBD from IBS with over 90% sensitivity and specificity. CRP levels showed a similar pattern: modestly elevated in IBS, substantially elevated in IBD.⁸

Microscopic colitis is another underappreciated mimic. This condition causes chronic watery diarrhea that can look and feel exactly like diarrhea-predominant IBS. Patients with microscopic colitis score significantly higher on IBS symptom scales than healthy controls, and the condition is invisible on standard colonoscopy because the inflammation only shows up under a microscope in biopsy samples.⁹ While microscopic colitis does not typically cause high fevers, it can produce low-grade temperature elevation and is associated with autoimmune conditions like thyroid disease and rheumatic disorders that carry their own fever risks.

Small intestinal bacterial overgrowth, known as SIBO, is yet another condition that shares many symptoms with IBS, including abdominal pain, bloating, gas, and diarrhea.¹⁰ In severe cases, the bacterial overgrowth can produce systemic symptoms including low-grade fevers, and the overlap between SIBO and IBS is substantial enough that some researchers have questioned whether a subset of IBS cases are actually undiagnosed SIBO.

Stress, the Autonomic Nervous System, and Feeling Feverish

Many people with IBS report feeling flushed, clammy, or experiencing chills during symptom flares without registering an actual fever on a thermometer. This disconnect between feeling feverish and being feverish likely has roots in the autonomic nervous system, which is the branch of the nervous system that controls involuntary functions like heart rate, blood pressure, digestion, and body temperature regulation.

Research has documented measurable differences in autonomic function between IBS patients and healthy controls, including altered heart rate variability and changes in blood pressure regulation.¹¹ These autonomic imbalances help explain why an IBS flare can feel like more than just a gut problem. When the autonomic nervous system is dysregulated, you can experience waves of sweating or chills, skin flushing, a racing heart, and a general sense of being unwell that mimics an infectious illness even though there is no infection.

There is also the phenomenon of psychogenic fever, sometimes called stress-induced hyperthermia. Psychological stress can genuinely raise core body temperature through pathways that are distinct from infectious fever. In some individuals, acute emotional stress produces a temporary spike in body temperature, while chronic stress can sustain a persistent low-grade elevation in the range of 37 to 38 degrees Celsius. The mechanism involves the sympathetic nervous system driving heat production rather than the inflammatory molecules that cause fever during an infection.¹² Given that IBS is strongly linked to psychological stress and anxiety, and that IBS flares are often triggered by stressful events, this pathway could explain why some patients notice temperature changes during bad episodes. The rise is usually mild and would not register as a clinical fever in most medical settings, but it is real and measurable.

Medication Side Effects Worth Considering

If you are taking medications for IBS or related conditions and notice fevers, the drugs themselves deserve a look. Drug fever is a recognized adverse reaction that can accompany a wide range of medications, and it is common enough that clinicians are specifically trained to consider it as a diagnosis of exclusion.¹³ People with IBS often take multiple classes of medication, from antispasmodics and antidepressants to proton pump inhibitors and antibiotics (particularly rifaximin, which is used to treat SIBO and IBS with diarrhea). Any of these can, in susceptible individuals, produce a febrile response.

Drug fever typically resolves within a few days of stopping the offending medication, and the pattern that should make you suspicious is a fever that started shortly after beginning a new drug or increasing a dose, without any other clear infectious source. If you are managing IBS with medications and experiencing unexplained low-grade fevers, it is worth discussing the timeline with your doctor before assuming the fever is unrelated.

When to Take a Fever Seriously

Because IBS is so common and its symptoms are so variable, it can be tempting to fold new symptoms into the “just my IBS acting up” category. Fever is one symptom that should not get that treatment. As discussed above, it is specifically flagged in diagnostic guidelines as a reason to look beyond IBS for an explanation.¹ A few scenarios in particular warrant prompt medical attention:

Fever above 38°C (100.4°F): This is outside the range that stress or autonomic dysfunction would explain and suggests an infectious or inflammatory cause.
Fever with bloody stool: The combination raises concern for IBD, infectious colitis, or other conditions that need specific treatment.
Fever with weight loss: Unintended weight loss paired with fever is not an IBS pattern and should be evaluated promptly.
New fever in established IBS: If you have had stable IBS for years and suddenly start having fevers with flares, the question is what changed, not whether IBS can do this.

A fecal calprotectin test is one of the most useful first steps. Because calprotectin levels in IBS are nearly identical to those in healthy people but are dramatically elevated in IBD, a normal result can be very reassuring, while an elevated one points toward further investigation with colonoscopy and biopsies.⁸ A basic blood panel with CRP and a complete blood count adds further clarity. These tests are simple, widely available, and effective at separating functional gut disorders from inflammatory ones.

Chills Without Fever in IBS

Chills deserve a separate mention because they are more commonly reported by IBS patients than actual fevers, and they do not necessarily mean the same thing. The shivering, goosebump-raising sensation of chills can occur without any rise in body temperature. In the context of IBS, chills during a flare are most likely related to autonomic nervous system activation, particularly the sympathetic “fight or flight” response. When your gut is in distress and sending alarm signals to the brain, the downstream effects can include vasoconstriction in the skin (making you feel cold), sweating, trembling, and a general sensation of being chilled.

This is not dangerous, but it is unpleasant and can be alarming if you interpret chills as evidence of an infection. The distinction is relatively simple: if you feel chilled but your temperature is normal or only trivially elevated, that is consistent with autonomic activation during a flare. If you feel chilled and your temperature is genuinely elevated above 38°C, that is a fever with chills and has a different set of possible causes.

Mast Cell Activation and Emerging Research

An area of growing interest in IBS research involves mast cells, a type of immune cell found throughout the gut lining. Mast cells release histamine and other mediators when activated, and increased mast cell activity has been documented in the colonic tissue of some IBS patients. There is a related condition called mast cell activation syndrome, in which mast cells release their contents inappropriately and in excess, producing a wide range of symptoms including flushing, diarrhea, abdominal cramping, and sometimes fever or temperature instability.¹⁴

The overlap between mast cell activation syndrome and IBS is an active area of investigation, and it is too early to draw firm conclusions about how often one is mistaken for the other. But it represents one plausible mechanism by which someone diagnosed with IBS might experience temperature fluctuations and a sensation of feeling feverish. If your IBS symptoms are accompanied by flushing, hives, or reactions to certain foods that seem out of proportion, this is worth raising with a gastroenterologist who is familiar with mast cell disorders. The research is still catching up, but awareness of the condition is increasing, and testing is available for patients whose symptom pattern suggests it.

1
PubMed Central. Predictive value of alarm symptoms in Rome IV irritable bowel syndrome: A multicenter cross-sectional study
2
PubMed. “Red flag” evaluation yield in irritable bowel syndrome
3
Journal of Neurogastroenterology and Motility. From Cytokines to Toll-Like Receptors and Beyond – Current Knowledge and Future Research Needs in Irritable Bowel Syndrome
4
Tropical Gastroenterology. Pro-inflammatory and anti-inflammatory cytokine response in diarrhoea-predominant Irritable bowel syndrome patients
5
PubMed Central. Post-infectious irritable bowel syndrome
6
PubMed Central. Post-infectious IBS: Defining its clinical features and prognosis using an internet-based survey
7
PubMed. Systematic review and meta-analysis: The incidence and prognosis of post-infectious irritable bowel syndrome
8
PubMed Central. Role of Calprotectin, IL-6, and CRP in Distinguishing Between Inflammatory Bowel Disease and Diarrhea Predominant Irritable Bowel Syndrome
9
PubMed Central. Irritable bowel syndrome-like symptoms in treated microscopic colitis patients compared with controls: a cross-sectional study
10
Academic Press / ScienceDirect. Clinical and Basic Neurogastroenterology and Motility – Chapter 24 – Small intestinal bacterial and fungal overgrowth
11
PubMed Central. Baroreflex mechanisms in Irritable Bowel Syndrome: Part I. Traditional indices
12
PubMed Central. Psychogenic fever: how psychological stress affects body temperature in the clinical population
13
PubMed Central. Drug fever: a narrative review
14
PubMed Central. Mast cell activation syndrome: Current understanding and research needs