My son has high fever! What’s going on in his body?

Last week my son had a flu-like thing with high fever, runny nose, and a bad cough. For me, 6 nights of 39°C+ temperature means lots of sleepless hours and more work because of a very grumpy toddler who refuses to have his syrup, his nose cleaned, his food and even most of the entertainment I find for him. But what does high fever mean for my son? Well, certainly no play cafes and no contact with other kids, but what is going on in his body when he has a fever?

Our normal body temperature fluctuates about 1°C during the day with a tendency to increase towards the evening. Body temperature also changes depending on, for example, the heat of the environment or physical exercise but goes back to normal quickly once such factors are removed. Different people have different ‘normal’ body temperatures, but if the temperature rises to levels higher than the expected daily values, then the person is said to have a fever. (1)

Fever is a natural reaction of the body in response to infection and inflammation. The aim of fever is to facilitate the survival of the host in the battle that it gives during an illness or disease. So, to start with, fever is not a bad thing.

Body temperature is regulated by the hypothalamus region of our brain, which works pretty much like a thermostat when it comes to body temperature. There is a set point for body temperature that is required and comfortable for all the working systems of our body. Under normal conditions, this set point in the hypothalamus doesn’t change and the nervous system maintains our body temperature accordingly. In the case of an infection, our immune system, which has been fighting against the infectious microbes, sends messages to the hypothalamus asking to raise this set point. In turn, the hypothalamus tells the nervous system to increase heat production, for example, via shivering, resulting in higher body temperature, namely fever. There is also evidence that the hypothalamus reacts to microbial products (secretions of the infectious microbes) even in the absence of messages from the immune system, also resulting in fever. (2)

Fever helps soldiers of our immune system to fight more efficiently during an illness. Fever also provides an environment where infectious agents such as bacteria and viruses reproduce slower than usual.

Does this mean fever should not be treated? If the person with a fever is feeling uncomfortable or has accompanying symptoms that require action, it should be treated. However, when it comes to fever in our children, it looks like that we are generally over-worried, something that the literature has named “fever-phobia”, which results in over-use of medical services and fever-relief drugs (3). Children often get fever due to minor illnesses like colds, medical treatment is only necessary if the fever persists for a long time or there are other serious symptoms (4). There is not sufficient scientific evidence supporting or opposing the safety of fever-relief drugs such as paracetamol and ibuprofen (4, 5). So in minor cases of fever, the general consensus is to use fever-relief drugs only to improve the child’s comfort and not to give them routinely (3, 4).

Personally, I am more worried when my son has a bad cough than when he has a fever. Nevertheless, it seems that my fever-tolerance is 39°C and above, particularly when I see that glassy-eyed look or hear him moaning and waking up at night. Then, I choose to give appropriate doses of paracetamol or ibuprofen to make him feel better, and it helps.



1- Sund-Levander et al., (2002). Normal oral, rectal, tympanic and axillary body temperature in adult men and women: a systematic literature review. Scand J Caring Sci.,16 (2), pp.122-128. Pubmed: 12000664

2- Dinarello, C.A. (2004). Infection, fever, and exogenous and endogenous pyrogens: some concepts have changed. J Endotoxin Res., 10(4), pp.201-222. Pubmed: 15373964

3- Crocetti M. Et al., (2001). Fever Phobia revisited: have parental misconceptions about fever changed in 20 years? Pediatrics, 107(6), pp.1241-1246. Pubmed: 11389237

4- Sullivan J.E. et al., (2011). Clinical report from the American Academy of Pediatrics: fever and antipyretic use in children. Pediatrics, 127(3), pp.580-587. Accessed online

5-  Perrott, D.A. et al., (2004). Efficacy and safety of acetminophen vs ibuprufen for treating children’s pain or fever: a meta-analysis. Arch Pediatr Adolesc Med.,158(6), pp.521-526. Pubmed: 15184213


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