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Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Rigors article more useful, or one of our other health articles.

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What is a rigor? (Description)

A rigor is an episode of shaking or exaggerated shivering which can occur with a high fever. It is an extreme reflex response which occurs for a variety of reasons. It should not be ignored, as it is often a marker of significant and sometimes serious infection (most often bacterial). It is important to recognise the patient's description of a rigor and to be aware of the possible significance of this important symptom.


Shivering is a reflex which occurs when someone feels cold and, physiologically, it serves to raise body temperature.1 The trigger point at which this reflex occurs is set in the anterior hypothalamus. This has been likened to an internal thermostat.

During infection or inflammation, pyrogens (cytokines and prostaglandins) 'reset' the trigger temperature so that the body feels cold and shaking occurs to raise temperature to the new hypothalamic 'temperature point'. The body's attempts to raise temperature are accompanied by other familiar reflex responses, including contraction of erector pilae muscles ('goose bumps') and peripheral vasoconstriction. Peripheral vasoconstriction causes cold extremities and pallor.

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How common are rigors? (Epidemiology)

Rigors are a common accompaniment of high fever.

  • They occur more commonly in children.

  • They are less likely to occur in the elderly.

  • They are a predictor of bacteraemia and bacterial infection in young and old.

Symptoms of rigors (presentation)


  • The sudden attack of severe shivering accompanied by a feeling of coldness ('the chills') is called a rigor and is associated often with a marked rise in body temperature. It may be described by patients as an attack of uncontrollable shaking.

  • A history of rigors should raise suspicion of infection, particularly bacterial infection. Enquiry should be made about:2

    • Symptoms suggestive of local infection, particularly respiratory infections, urinary infections, open wounds and possible skin infections, biliary disease, and gastrointestinal (GI) infections.

    • Recent surgical procedures.

    • Any relevant past medical history such as rheumatic heart disease.

    • Recent foreign travel.3

    • Medication and allergies.


  • This should be performed according to the history.

  • Care should be taken in children where even an otitis media or upper respiratory infection may have triggered a rigor.

  • It should be remembered that rigors can be an early symptom in septicaemia, particularly meningococcal septicaemia. Appropriate care should be taken to examine for rashes as well as signs of meningism, especially in children.

  • A history of rigors in the night may be followed by signs of a pneumonia the next day - rigors may be seen early in the natural course of an infective process.

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Differential diagnosis

The classic differential diagnosis for rigors includes:

  • Biliary sepsis (part of Charcot's triad).

  • Pyelonephritis.

  • Visceral abscess (including lung, liver and paracolic).

  • Malaria.

It is important in children to differentiate a rigor from a febrile convulsion. In adults, care should be taken to differentiate from a fit or convulsion. There is a wide range of conditions that can be associated with rigors, such as:





  • Over half of women in labour experience shaking rigors.

  • Data indicates that the cause is likely multifactorial. Significant predictors include high pain scores, hypothermia with vasoconstriction, epidural use, fever and low mean skin temperature.


Infectious diseases


Medication reactions (usually intravenous)

Transfusion reactions

  • 30% of transfusion reactions are associated with rigors.

  • Many types of blood product transfusions.



  • Haemodialysis.

  • After radiotherapy.

  • After bone marrow transplant.

  • Catheterisation.

  • Postoperative infections.

Diagnosing rigors (investigations)

This will depend on the clinical assessment and likely cause. Very often history and examination will reveal a source of infection and treatment can be commenced without extensive investigation. However, in children, extreme care should be taken and hospital admission will usually be indicated, particularly when the child remains febrile and no source of infection is found - the pyrexia of unknown origin (PUO).4

The following list is not exhaustive. In particular, an ill child investigation is likely to include:

  • Screening for infection, and basic blood tests:

    • FBC, U&Es, ESR, CRP, and LFTs.

    • Blood cultures.

    • Urine for microscopy and culture.

    • Lumbar puncture and cerebrospinal fluid analysis.

  • Imaging:

    • CXR.

    • CT and / or MRI scans.

Management of rigors

  • Infection-related rigors can be managed with temperature-lowering general measures, particularly in children. Antipyretic agents should not routinely be used with the sole aim of reducing the body temperature of a child with fever. However, if they are distressed due to a fever then antipyretics are recommended.5

  • It is important to find and treat the source of infection6 .

  • It is likely that hospitalisation will be required for diagnosis and treatment if the patient remains unwell and febrile. Admission to hospital is more likely to be required in children and in the elderly.

  • Other causes of rigors will have specific treatment regimes and it is beyond the remit of this article to detail all.

Further reading and references

  1. Dall L, Stanford JF; Fever, Chills, and Night Sweats
  2. Martin Lee LAM, Goldstein S; EMS, Clinical Diagnosis Without The Use Of A Thermometer
  3. Davidson H, Houston A; Fever in the returning traveller. Medicine (Abingdon). 2021 Nov;49(11):723-726. doi: 10.1016/j.mpmed.2021.08.005. Epub 2021 Sep 29.
  4. Barbi E, Marzuillo P, Neri E, et al; Fever in Children: Pearls and Pitfalls. Children (Basel). 2017 Sep 1;4(9). pii: children4090081. doi: 10.3390/children4090081.
  5. Fever in under 5s: assessment and initial management; NICE Guidance (last updated November 2021)
  6. Brown I, Finnigan NA; Fever of Unknown Origin.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • Next review due: 26 Sept 2028
  • 28 Sept 2023 | Latest version

    Last updated by

    Dr Surangi Mendis

    Peer reviewed by

    Dr Pippa Vincent, MRCGP
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