When a child is sick - whether it's a cough, a runny nose or an earache - there is one thing that is particularly important to parents.

With a worried look they ask: Do you have a fever?

First they feel with their hands whether their foreheads are hot, then they pull out the thermometer.

But what exactly is fever?

And what's so dangerous about that?

Johanna Kuroczik

Editor in the "Science" department of the Frankfurter Allgemeine Sunday newspaper.

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The word "fever" comes from Latin.

"Febris" means something like heat, and it's true: Having a fever means that the core body temperature is rising.

Normally we have between 36.5 and 37.5 degrees inside.

With this heat, all our organs can work well.

During the day it can also be a bit warmer or colder.

In the evening we are a little warmer than in the morning.

And if, for example, a child has just romped wildly, the thermometer will show more than 37.5 degrees for a short time.

When you're sick, your internal temperature rises and your forehead gets hot, as does the rest of your body.

One speaks of fever from 38 degrees, and from 39 it is considered "high".

If the temperatures are longer than 40 degrees, then parents and doctors are quite concerned.

That's why it's hard to believe that fever is actually a brilliant thing.

The internal heat serves as a tool for our body to fight a burgeoning disease.

Colds, flu or earaches are caused by pathogens, bacteria or viruses.

These organisms are so tiny that they can only be seen under special microscopes.

For example, we breathe them in when someone nearby sneezes or coughs.

These invaders then wreak havoc on the body, causing pain and inflammation.

In the worst case, they can even kill us.

Fortunately, the body has its own defenses – the immune system.

This includes a wide variety of cells that patrol our bodies like tiny police officers or specifically attack bacteria.

And the entire defense system can work better when it's a little warmer in the body - the immune cells are more active and mobile between 38 and 40 degrees.

Another benefit of internal heat is that bacteria don't like it.

It is more difficult for them to multiply when the body temperature is 39 degrees instead of 37. Fever is therefore a protective mechanism.

Children get fevers faster than adults.

But how exactly do we turn up our inner heating?

That's a bit complicated.

When defense cells of the body's immune system encounter pathogens, they release special messenger substances.

They have the difficult name pyrogens.

These then rush to the brain to sound the alarm.

Our thinking organ consists of around 86 billion nerve cells, and it is well known that everything is coordinated here, every thought and every movement.

Of course, there is also a control center that is responsible for regulating our heat balance.

When the messenger substances arrive there, in the so-called hypothalamus, the nerve cells raise the target temperature in the body.

A little like turning on a heater.

And especially those who live in an older house know what happens first - the heating gurgles and roars, it has to work properly,