Rigors - Symptoms

Authored by Dr Mary Lowth, 30 May 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Prof Cathy Jackson, 30 May 2017

A rigor is an episode of shivering and feeling very cold whilst your body temperature rises above normal, followed by an episode of feeling very warm whilst your body temperature falls again. During the 'feeling cold and shivery' phase, other people will feel that you are hot to the touch although you'll feel as if you are too cold. During the 'feeling hot and sweaty' phase, you will feel as if you are too hot, and other people will notice you are flushed and sweaty. Rigors last varying amounts of time, from minutes to hours. They may occur repeatedly.

If you read novels or watch TV dramas set in the pre-antibiotic era, you may be familiar with the idea that when people were sick with infectious diseases they would be put to bed, pale and unwell. Sometimes they were said to be 'delirious', as the temperature and illness made them confused. This was a frightening experience, because at this point they were becoming more unwell, as their temperature (fever) increased. In those days the most common causes were infections like pneumonia, which were often deadly.

Eventually the temperature would stop rising. Everyone would be relieved because 'the fever had broken'. 'Breaking' was the point at which the fever had reached its peak, the shivering stopped and the patient became flushed and started to sweat. This was greeted with relief, as it meant that the body temperature was starting to return towards normal. People believed that the battle against infection was won and the patient was recovering. Whilst this was not always the case, as sometimes further rigors occurred, it was often true that the worst was over.

What is being described is a rigor. In pre-antibiotic times the most common causes would have been bacterial pneumonia, and multiple different childhood infections like scarlet fever and measles.

It is important to know the difference between a rigor, a febrile convulsion and a fit (seizure).

During a rigor the affected person will be shivery (and may be shaking violently). They may be confused (particularly when their temperature is high) but during a rigor they will be conscious, and will respond to you - for example, by obeying commands like: "Open your eyes."

Febrile convulsions are a type of fit that can happen when a child, between the ages of 6 months and 6 years, has a high temperature (fever). During a febrile convulsion your child will not be conscious and will not respond to you. A febrile convulsion lasts anything from seconds to about five minutes. See separate leaflet called Febrile Seizure (Febrile Convulsion) for more information.

A fit is like a febrile convulsion but it may occur at any age. During a fit the patient will not be conscious and will not respond to you. A fit in a person who is unwell is suggestive of illness affecting the brain (such as stroke or meningitis). Fits may also arise in people who have an increased tendency to fits - a condition called epilepsy. See separate leaflet called Epilepsy - a General Introduction for more information.

Rigors can happen in anyone who has an infection and experiences a sudden rise in temperature. Rigors are more common in children, who tend to develop higher temperatures than adults in response to infection. Older adults, particularly the very elderly, have less reactive immune systems, and are less likely to experience rigors.

The term 'rigor seizure' or 'rigor fit' is widely discussed on the internet, with people asking what it is on several websites. Rigors and fits are separate things. Some people refer to the violent shivering of a rigor as a 'rigor seizure' or 'rigor fit' - but these are confusing terms which are better avoided as they make it unclear what has happened (ie was it a rigor, or a fit, or both?).

Whilst it is possible (although quite unusual) to have a rigor and a fit at the same time (as the same underlying illness could cause both to occur simultaneously), they are two very different things.

A rigor may involve violent and uncontrollable shivering, sometimes with mild confusion, but the patient remains conscious and can respond to you. A fit (seizure) may also involve jerky shiver-like movements, but patients are not aware of their surroundings and do not respond to you.
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