--- topic: "Fever" title: "Fever: Friend or Foe?" order: 1 description: "How fever helps fight infection, why treating it is for comfort rather than the number, and the red flags in babies, children, adults and pregnancy." question: "Should you bring a fever down or let it run its course?" answer: "A fever likely helps your body fight infection, so treat it only for comfort, not to hit a number, and know the red flags." actions: - "Judge by how the person looks and acts, not the thermometer: a distressed child can have paracetamol or ibuprofen (never both at once), and the aim is comfort [2][3]." - "Offer regular fluids, dress comfortably without over-wrapping, and skip tepid sponging, which NICE does not recommend [3]." - "Check the red flags below, and trust your instinct: a parent's strong worry was one of the best predictors of serious infection [10]." cautions: - "Urgent help for a baby under 3 months with fever (38°C/100.4°F+), a rash that does not fade under glass, stiff neck, bulging soft spot, fit or fast, labored breathing [3][10]." - "Adults with fever plus severe headache, a stiff neck or confusion need emergency care, and a fever in early pregnancy deserves a call to your clinician [11][12]." - "A child's fever lasting 5 days or more needs assessment, and fever medicines do not prevent febrile seizures, so call a doctor if a child has a fit [3][9]." confidence: 3 confidenceNote: "Guidelines agree and trials found no benefit from lowering fever, but evidence that fever speeds recovery comes mostly from animals, and few trials cover ordinary illness." evidenceSummary: rctCount: 4 observationalCount: 1 metaAnalysisCount: 3 totalParticipants: "2,100+ (plus pooled analyses)" replicated: true newestStudyYear: 2021 references: - id: "1" pmid: "25976513" title: "Fever and the thermal regulation of immunity: the immune system feels the heat" authors: "Evans SS, Repasky EA, Fisher DT" year: 2015 journal: "Nat Rev Immunol" - id: "2" pmid: "21357332" title: "Fever and antipyretic use in children" authors: "Sullivan JE, Farrar HC; Section on Clinical Pharmacology and Therapeutics; Committee on Drugs" year: 2011 journal: "Pediatrics" - id: "3" url: "https://www.nice.org.uk/guidance/ng143" title: "Fever in under 5s: assessment and initial management" authors: "National Institute for Health and Care Excellence" year: 2021 journal: "NICE guideline NG143" - id: "4" pmid: "20929891" title: "The effect on mortality of antipyretics in the treatment of influenza infection: systematic review and meta-analysis" authors: "Eyers S, Weatherall M, Shirtcliffe P, et al." year: 2010 journal: "J R Soc Med" - id: "5" pmid: "2172402" title: "Adverse effects of aspirin, acetaminophen, and ibuprofen on immune function, viral shedding, and clinical status in rhinovirus-infected volunteers" authors: "Graham NM, Burrell CJ, Douglas RM, et al." year: 1990 journal: "J Infect Dis" - id: "6" pmid: "2656959" title: "Acetaminophen: more harm than good for chickenpox?" authors: "Doran TF, De Angelis C, Baumgardner RA, et al." year: 1989 journal: "J Pediatr" - id: "7" pmid: "26436473" title: "Acetaminophen for Fever in Critically Ill Patients with Suspected Infection" authors: "Young P, Saxena M, Bellomo R, et al." year: 2015 journal: "N Engl J Med" - id: "8" pmid: "16433601" title: "The effect of antipyretic therapy upon outcomes in critically ill patients: a randomized, prospective study" authors: "Schulman CI, Namias N, Doherty J, et al." year: 2005 journal: "Surg Infect (Larchmt)" - id: "9" pmid: "23702315" title: "Do antipyretics prevent the recurrence of febrile seizures in children? A systematic review of randomized controlled trials and meta-analysis" authors: "Rosenbloom E, Finkelstein Y, Adams-Webber T, et al." year: 2013 journal: "Eur J Paediatr Neurol" - id: "10" pmid: "20132979" title: "Diagnostic value of clinical features at presentation to identify serious infection in children in developed countries: a systematic review" authors: "Van den Bruel A, Haj-Hassan T, Thompson M, et al." year: 2010 journal: "Lancet" - id: "11" pmid: "15509818" title: "Clinical features and prognostic factors in adults with bacterial meningitis" authors: "van de Beek D, de Gans J, Spanjaard L, et al." year: 2004 journal: "N Engl J Med" - id: "12" pmid: "15703536" title: "Maternal hyperthermia and the risk for neural tube defects in offspring: systematic review and meta-analysis" authors: "Moretti ME, Bar-Oz B, Fried S, et al." year: 2005 journal: "Epidemiology" --- Fever is part of how your body fights infection, and lowering it has not been shown to speed recovery [1][2][7]. The aim is comfort, not a number, and fever medicines do not prevent febrile seizures [3][9]. What matters more is how the person looks and acts, plus a short list of red flags: a very young baby, a rash that does not fade, a stiff neck, trouble breathing, or a fever lasting five days [3][10]. ## How it works ### What a fever is A fever is a deliberate rise in your temperature set point, driven by immune signals such as interleukin-6. The heat helps immune cells activate and travel to lymph nodes, though most of that evidence comes from animals and cells [1]. The American Academy of Pediatrics describes fever as a beneficial mechanism rather than an illness, and finds no evidence that fever itself worsens an illness or causes long-term neurologic harm [2]. ### Should you bring it down? Only for comfort. NICE advises against using fever medicines with the sole aim of lowering temperature. For a distressed child, paracetamol (acetaminophen) or ibuprofen can be used until they settle, not both at once, and neither prevents febrile seizures [3][9]. The AAP finds the two similarly safe and effective in healthy children [2]. Tepid sponging is not recommended, children should not be over-wrapped, and regular fluids matter [3]. See [what to eat and drink when sick](/what-to-eat-when-sick/what-to-eat-and-drink-when-ill). Whether fever medicine slows recovery is unsettled. In animals, antipyretics raised influenza deaths, and no human trials have measured deaths [4]. In small human trials they dulled the antibody response in cold-virus volunteers and slowed scabbing in chickenpox [5][6]. In critically ill adults, a 700-patient trial found no difference in outcomes, while a smaller trial stopped early after more deaths, not statistically significant, with aggressive cooling [7][8]. ### Red flags: when a fever needs a clinician - A baby under 3 months with a temperature of 38°C (100.4°F) or higher, or a baby of 3 to 6 months at 39°C (102.2°F) or higher [3]. - A rash that does not fade under a pressed glass, a stiff neck, a bulging soft spot, or a fit [3]. - Fast or labored breathing, blue, mottled or ashen skin, or a child who is hard to wake, unresponsive or crying weakly [3][10]. - Dry mouth, sunken eyes, no tears or very little urine [3]. - A child's fever lasting 5 days or longer [3]. - In adults, fever with severe headache, a stiff neck or confusion [11]. - Fever or overheating early in pregnancy, which is linked to neural tube defects [12]. - A parent's strong sense that something is wrong [10]. ## The evidence in detail ### Does fever help? Evans, Repasky and Fisher reviewed how the heat of fever stimulates innate and adaptive immunity, including a role for interleukin-6 in mobilizing lymphocytes to lymph nodes, and describe fever as conserved for over 600 million years of vertebrate evolution with a survival benefit during infection [1]. Almost all of that evidence is from animals and cells. The one meta-analysis that asked the human question, by Eyers and colleagues, found no human trials: all eight eligible studies, from three publications, were in animals. Antipyretics (aspirin, paracetamol, diclofenac) increased the risk of death in influenza-infected animals, with a pooled odds ratio of 1.34 (95% CI 1.04 to 1.73) [4]. ### What human trials show Graham and colleagues gave 60 healthy volunteers rhinovirus type 2 and randomized them to aspirin, acetaminophen, ibuprofen or placebo; 56 were infected. Aspirin and acetaminophen suppressed the serum neutralizing antibody response and increased nasal symptoms and signs (P<.05 versus placebo), and virus shedding tended to last longer, though not significantly [5]. In Doran's double-blind trial in children with chickenpox (31 on placebo and 37 on acetaminophen 10 mg/kg four times a day for four days), time to total scabbing was 5.6 days on placebo and 6.7 days on acetaminophen, and itching on day 4 was worse on acetaminophen; activity was better on acetaminophen on day 2 [6]. Both trials were small and measured surrogate outcomes. In critical care, Schulman randomized 82 trauma ICU patients to aggressive treatment (acetaminophen 650 mg every 6 hours above 38.5°C, plus a cooling blanket above 39.5°C) or permissive treatment (nothing until 40°C). There were 7 deaths in the aggressive group versus 1 in the permissive group (P=0.06), and the trial stopped at its first interim analysis [8]. The much larger HEAT trial randomized 700 ICU patients with fever of 38°C or more and suspected infection to 1 g of intravenous acetaminophen every 6 hours or placebo. ICU-free days to day 28 did not differ (23 versus 22 days; P=0.07), and 90-day mortality was 15.9% versus 16.6% (relative risk 0.96, 95% CI 0.66 to 1.39) [7]. Together they suggest that suppressing fever did not help critically ill adults, though neither trial is conclusive. ### Febrile seizures Rosenbloom and colleagues pooled three randomized trials of 540 children aged 6 to 72 months with a prior febrile seizure (348 given acetaminophen, ibuprofen or diclofenac, 192 given placebo) followed for one to two years. Seizures recurred in 22.7% on antipyretics and 24.4% on placebo (odds ratio 0.9, 95% CI 0.57 to 1.43) [9]. This is why NICE says antipyretics should not be used to prevent febrile convulsions [3]. ### How well do red flags work? Van den Bruel and colleagues reviewed 30 studies of children in ambulatory care. Cyanosis, rapid breathing, poor peripheral perfusion and a petechial rash were red flags in several studies. In one primary-care study, parental concern (positive likelihood ratio 14.4) and clinician instinct (23.5) were strong red flags. A temperature of 40°C or more helped only where serious infection is uncommon, and no single feature could rule serious infection out [10]. In adults, a Dutch study of 696 episodes of bacterial meningitis found the classic triad of fever, neck stiffness and altered mental status in only 44%, but 95% had at least two of headache, fever, neck stiffness and altered mental status; mortality was 21% [11]. For pregnancy, a meta-analysis of 15 studies (1,719 cases and 37,898 non-cases) linked maternal hyperthermia in early pregnancy to neural tube defects, with a pooled odds ratio of 1.92 (95% CI 1.61 to 2.29); it pooled observational studies, so it shows an association, not that fever caused the defects [12]. ### Where the evidence conflicts The animal case for fever is consistent but untested in people, and the human trials of fever-lowering are small, short or in intensive care. HEAT found no harm from acetaminophen, while Schulman hinted at harm from aggressive cooling [7][8]. Paracetamol and ibuprofen do relieve discomfort, and the AAP notes that combining them is more effective than either alone but more complicated and open to unsafe dosing [2]. The cold and chickenpox findings are modest, and their clinical importance is unclear [5][6]. ### Bottom line Confidence is moderate to low (3 of 5). Guidance from the AAP and NICE agrees that fever medicine is for comfort [2][3], trials show no benefit from lowering fever in critical illness [7], and antipyretics do not prevent febrile seizures [9]. That fever speeds recovery in people is plausible but rests mainly on animal and laboratory data [1][4]. The red flags matter more than the number on the thermometer [3][10][11].