How fever fights infection

If you’ve ever experienced fever, you’ll know it’s not very pleasant. It’s often accompanied by sweating, chills and shivering, headache, and other aches, including muscles.1

A fever is a warning that something out of the ordinary is going on within your body, and the most common cause is an infection.2

From a medical point of view, a fever is when your body temperature rises above your normal level, which is around 37oC. It can vary throughout the day, and can be different in women, at different times of the menstrual cycle, while older people tend to have slightly lower body temperatures than young people.2

To be a little more specific, the Australian Department of Health defines fever as 38oC or higher.3

So why does fever happen and what should we do about it?

Our immune system has evolved to use fever to protect us during infections. Scientists believe that bacteria and viruses find it more difficult to replicate and infect body cells when our body temperature is higher than normal, so the immune system tries to use that to its advantage.2

Early in an infection, when the immune system cells learn that there might be a germ invading the body, it releases biochemicals called pyrogens (pyro comes from the Greek word for fire), which act on the part of the brain that controls body temperature.4 The brain, in turn, releases hormones that cause a variety of heat-boosting actions. For example, the blood vessels in our skin constrict, so heat is contained in the body rather than released. Fat cells burn energy and muscles rapidly contract – that’s where the shivering comes from. All these actions lead to an increased body temperature.3,4

Given that our immune system has been ‘designed’ to fight infection with fever, should we be treating it or letting it run?

If our body temperature rises too high it can start to kill good body cells, putting us in danger.2 And a rise of just 1oC means our body must expend an extra 10% in energy.2 So if a person is frail or fighting other illness, it can increase the risk of health issues. Children and infants can be vulnerable and need to be carefully monitored too.

The following advice comes from the Department of Health (DOH)3:

  • See a doctor right away if your child has a fever and they are under 3 months, or if they are getting sicker, are drowsy and unresponsive, seem dehydrated or won’t drink, are vomiting, have a stiff neck or seem very distressed3
  • Adults with a fever should see a doctor straight away if they have a severe headache, sensitivity to bright light, unusual skin rash, stiff neck, vomiting, confusion, difficulty breathing, abdominal pain, a seizure or confusion3

You can find out more about what fever is dangerous in this article.

Fever can be reduced with paracetamol or ibuprofen.

The important thing is to monitor the temperature, especially in infants, young children, or the vulnerable. Digital thermometers are an affordable and convenient way to measure body temperature and keep an eye on fever, especially in children. There are many options available such as digital oral thermometers, Ear thermometers and non-contact thermometers. You can check out the Welcare and Omron ranges available on Smart Wellness here.

Always read the label and follow the directions for use.


  1. https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7195085/
  3. https://www.healthdirect.gov.au/fever
  4. https://www.scientificamerican.com/article/what-causes-a-fever/



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