Hot Garbage: Mythbusting fever in children

Alasdair Munro · Published 14 January 2020 · Updated 30 April 2026

Clinical

Juniper is a 3-year-old girl brought in with her mother with a 48-hr history of fever. Her mum is particularly concerned because her fever was up to 39.8°C, didn’t come down with paracetamol, and she describes an episode which sounds like a rigor. On examination, she has a temperature of 39.3°C, a runny nose and bright red tonsils, and looks otherwise well. You go to discharge her, but your colleague asks if you should wait to see if her temperature comes down with ibuprofen before sending her home.

Introduction

Febrile illnesses are the most common cause of presentation to acute paediatric medical services. This means that fever is the most common presenting symptom seen by paediatricians and a major cause of concern for parents. Despite this, it is clear that in day-to-day practice, there is a widespread misunderstanding of fever, its purpose, and its clinical interpretation.

Well, no longer! Once you have finished reading, you will be a master of all things related to fevers in children. We will start with a basic understanding of the processes surrounding fever and finish with some mega myth-busting!

What is fever?

Fever is an elevated core body temperature, part of a physiological response to infection regulated by the hypothalamus. This is crucial to understand – your body controls your temperature. This is not something an infection is doing to your body; it is something your body is doing to the infection. This differs from pathological hyperthermia, where your temperature is elevated by either hypothalamic dysfunction or external heat. These are extremely rare.

Note: there are other non-infectious causes of fever, such as cancer, Kawasaki’s, and autoinflammatory conditions, but these are rare compared to infectious fever and are covered elsewhere.

What temperature counts as a fever?

At what threshold do we say a child has an elevated body temperature? This is more controversial than one might think, as the data from which we derive “normal” body temperature is extremely poor. The most common cut-off for defining a fever is 38°C – but it is important to remember that there is nothing magic about 38°C compared to 37.9°C, and temperature is better taken in context or a trend, if possible.

How do we get fevers?

The process of developing fever is extremely complex, and our understanding is still developing. At present, our best explanation is that the process is triggered by chemicals known as pyrogens. Pyrogens can be either exogenous (such as components of the microbe itself, like the lipopolysaccharide on the outside of bacteria) or endogenous, such as cytokines like IL-1, TNF, Prostaglandin E2, and, importantly, IL-6, which are released by immune cells when they detect an invader. These pyrogens act to increase body temperature peripherally but, importantly, also trigger receptors in the preoptic nucleus of the brain. This releases PGE2 into the hypothalamus, which then sets a new target temperature. This target is met by many facets designed to increase heat, including:

It is important to remember that the body is trying to get hotter. If you intervene with non-medicinal efforts to cool it down, it will work even harder to try to heat up.

Why do we get fevers?

The process of fever has been conserved across species, from lizards to mammals, and even in plants! This is because it is a beneficial response to an infection. The mechanisms by which a fever helps protect you from infection include:

  1. Higher temperatures inhibit the growth/replication of pathogens
  2. Higher temperatures promote the immune response to infection

It is worth noting that bacteria are killed more easily by antibiotics at higher temperatures, suggesting a potential third mechanism.

Summary

Fever is beneficial. When a pathogen causes infection, pyrogens stimulate the hypothalamus to increase body temperature through several mechanisms. This increased temperature helps inhibit the pathogen’s growth AND stimulates the immune system to fight it.

That was a lot of science. Don’t worry – it’s time to get clinical! All this science stuff is lovely, but what does this mean for our patients?

Clinical significance of fever

As we have ascertained, fever is beneficial. For this reason, it is of no concern when a child presents with fever alone. We are interested in the cause of the fever. Is this fever the result of a benign, self-limiting childhood infection – or is it associated with a severe bacterial infection? Trying to determine whether this is enough for its blog article (the most important thing is the end-of-the-bed assessment – see Andy Tagg’s excellent breakdown of the paediatric assessment triangle).

Ignore the fever itself – what’s important is ascertaining its cause.

Now, let’s bust some myths that persist about fever in children!

Myth 1 – Higher temperature indicates a serious infection

This is one of the most common concerns among parents. The specific temperature may be what prompts them to come to hospital, or what drives the health care provider to initiate more aggressive management or investigations.

The truth is that the relationship between the height of temperature and risk of serious illness is at best complicated, and at worst a dangerous distraction. There is a very poor correlation, with such woeful sensitivity and specificity that it will both grossly over- and under-call serious infections (whether the high temperature is used to rule in or the lower temperature to rule out). The caveat to this is that in younger infants (particularly under 60 or 90 days), who have a higher baseline risk of serious infections (and more to the point, once they spike a temperature, it will be managed aggressively regardless of how high it was).

Some studies have shown a weak association in older children, but not enough to have any meaningful influence on our management. A fever is a fever – higher temperatures should not be managed differently from lower ones.

Myth 2 – Temperature not relieved by antipyretics indicates a serious infection

Another common misconception is also linked to the myth above. Some fevers respond well to antipyretics, and some do not. We do not understand why this is the case. However, studies have not demonstrated that failure to respond to antipyretics is a helpful indicator of a more serious infection. It is not very pleasant for the child to remain hot, but it does not mean they are at any higher risk. A child whose temperature does not respond to antipyretics should not be treated any differently from one that does.

Myth 3 – Rigors indicated a serious infection

This has been covered in a separate blog post – but to summarise, there is extremely weak evidence that rigors are associated with an increased risk of bacterial infection in children, which is irrelevant when more important factors are taken into account. There is also evidence of no increased risk. The presence or absence of rigors should not be a deciding factor in managing febrile children.

Myth 4 – You must wait for a fever to come down before discharge

This may seem common practice for many of you working in acute paediatrics. If a child is febrile on arrival, people often want to wait for the temperature to come down before allowing them to be discharged (this should be distinguished from observing that observations normalise in the absence of fever, which is a more understandable, if still slightly questionable, practice). As we have seen, a fever merely indicates the presence of an infection.

If you have ascertained the cause of the fever or at least ruled out any red flags for serious causes, the ongoing presence or absence of a fever means nothing for the child. If it comes down before discharge, it will probably go back up once they are home! There is no need to make them wait for hours for no reason.

Myth 5 – Fever should be treated with antipyretics

We have established that fever is beneficial. Therefore, there is essentially no reason to treat a fever in and of itself. It will not cause harm, and it is probably helping. Some children tolerate higher temperatures exceptionally well, so if they are playing happily or do not seem terribly bothered by a temperature of 39°C, then you leave them well alone.

Treat the child, not the fever.

Myth 6 – Fever should not be treated with antipyretics

There is an opposing school of thought, which says that since fevers are beneficial, we should not treat them at all. Given how absolutely dreadful it can feel to have a fever (which many of us adults can vouch for), many of us give medicine to try to bring the temperature down and make the child more comfortable. This is the right thing to do.

Despite the potential benefits of fever, there is no evidence of clinically significant harm from treating fever in unwell children or adults in the ICU. If the child is distressed by the temperature, they should be given antipyretics to help them feel more comfortable.

Summary

Postscript: Febrile convulsions

When I posted my initial thread on Twitter about fevers, many comments asked why I didn’t address febrile convulsions. This was mainly because these are worth their own post (which they have here). In brief, febrile convulsions are extremely distressing for parents to observe, but they are common, and they are very benign. We do not advise treating fevers to prevent febrile convulsions, and until recently, this was because there was no evidence that they had any effect in preventing them. A recent study from Japan did demonstrate a decrease in the recurrence of febrile convulsions in children who had already had one if given regular PR paracetamol; however, there are significant caveats to this study discussed in depth here.

For the more visually oriented, the talented Emma Buxton has created an infographic of the key reminders from this blog post:

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