Fevers: a simple explanation
The goal of this post is to explain why fever happens. And, hopefully, understanding why and how it happens will make you less freaked out the next time your child has a fever.
Your pediatrician has probably told you fevers are part of a healthy immune response. But do you believe them?
When your child feels warm, its easy to spiral, worry & fixate on “getting the temperature down”- and if you spend any time on google, you’ll find enough misinformation about fevers that you may end up confused.
But as with most things, understanding can help alleviate fear. So lets get into it.
Basic physiology
Your body - like your house - has a thermostat. It lives in the hypothalamus, and typically keeps body temperatures within a specific range.
When an inflammatory or infectious process is detected (such as the start of a virus), the body’s response includes releasing inflammatory markers, such as cytokines. These have multiple different jobs in managing our immune response, from helping guide infection-fighting white blood cells to where they need to go to telling the hypothalamus that it is time to adjust the thermostat.
Why adjust the thermostat?
Increasing the body’s core temperature makes the body’s immune response more effective. It increases the heart rate and breathing rate, to optimize metabolic function - there is better oxygenation and blood flow to help support the immune reaction. For some pathogens, higher temperatures can also make the environment less hospitable. Both obviously help.
What happens next?
By adjusting the thermostat and changing the “set point” - the hypothalamus instructs the body to “increase the core temperature.” A healthy body then follows that instruction by trying to retain as much heat as possible. As the temperature is rising, you may see things like:
Shivering increases heat production in the muscles. This is why your child might shiver as their temperature is increasing (it seems backward, right?)
Vasoconstriction (or narrowing blood vessels) that go to the skin and extremities helps decrease heat loss through the skin. This is why skin, especially hands and feet, can become cool or clammy as the temperature is rising.
Once the core temperature is high, your body looks and acts hot: you may see flushed skin, sweating, or notice faster breathing or a more rapid heart rate. You also can get dehydrated more quickly.
The Pediatrician Mom Note: The elevated core temperature here is DIFFERENT from the elevated core temperature that can happen due to environmental heat exposure, which is termed hyperpyrexia. In that case, the body’s set point/thermostat is unchanged. The high core temperature quickly overwhelms the body’s capacity to react and compensate by losing heat.
So what does this all mean?
The elevated core temperatures as a result of fever are part of the normal immune reaction - they are not dangerous to the body.
The specific number on the thermometer doesn’t matter as much as the fact that a fever is present. We define fever as any temperature above 100.4F (or 38C).
Although the fever is not a cause for alarm, it is still true that whatever infection or process is causing the fever could be concerning, so we don’t ignore fevers. Pay attention, but there is no need to panic.
Organ damage can occur at extreme temps (over 107F). But this is more likely to happen due to heat exposure than an infection. A fever, even if high, is a controlled adjustment - and will not cause brain damage. With that said, an elevated core temperature that is sustained for a long time will eventually start to deplete the body’s reserve - this can cause problems. This is why we always recommend a healthcare provider evaluates a patient with ongoing symptoms.
Using cold/ice baths, washcloths, etc is not only uncomfortable, it doesn’t actually help (in fact, could increase the temp by inducing shivering). And your child likely feels cold - don’t withhold blankets because you’re worried about them elevating the temperature more.
The Pediatrician Mom Note: There are certain situations where any fever still requires an evaluation. Some examples are infants under 2 months, or children with underlying health conditions such as cancer or sickle cell disease. Talk to your healthcare provider and make a fever plan if you believe your child falls into these categories.
What about febrile seizures?
If your child has had one of these, you know how scary they are. Many parents who have dealt with these have an especially panicky reaction at the thought of their child having a fever - and a tendency to knee-jerk to giving fever reducers.
It is a common misunderstanding that febrile seizures occur because of high fevers. Actually, febrile seizures are thought to happen because of the cytokine inflammatory response… which is already in place by the time the temp is rising.
This means that (unfortunately), febrile seizures can happen even at low temperatures. (100.4F). They are more likely when a fever rises quickly - but this is because of the concurrent inflammatory response which is also happening quickly.
Because the fever itself is not the cause of the febrile seizure, several studies have found that giving fever-reducers does not prevent febrile seizures, which often occur at the start of an illness (PMID: 28225210, 19736332). I will note, though, that there is a single study that suggests that rectal Tylenol may decrease recurrent febrile seizures DURING A SINGLE illness (PMID: 30297499).
Febrile seizures have a hereditary component - they often run in families. And the good news is that for simple/short febrile seizures, the prognosis is good, and most kids outgrow them by age 5. For more complex or prolonged seizures, the recommendations and prognosis are more complicated.
So… does this mean we shouldn’t treat fevers?
No. Remember, fevers can make a child look and feel crummy. And children who feel bad are less likely to be cooperative with things like staying hydrated.
But it does mean that the focus should be on comfort, not on bringing down the temperature.
If your child has a fever but is perky, drinking and seems comfortable, you do not need to fixate on bringing their temperature down.
But Dr P! Doesn’t that mean their body isn’t able to fight the infection as well?
Sure. But you know what else interferes with fighting an infection effectively? Dehydration.
During an illness, your body needs fluids. Often with young children, dehydration/the need for intravenous fluids is what sends them to the hospital. Make sure to check out this post on how to tell if your child is dehydrated.
How to treat a fever:
Most pediatricians approach fevers with a holistic view - we treat the child, not the number. Here is an overview of my approach.
My theory: seeing your child sick activates a primal brain pathway that interferes with your ability to think rationally. It happens to me too!
Hopefully this post is one you can refer back to the next time your child has a fever - so that you can take a step back and think more clearly.
