When the brain has decided that you will have a fever, something strange happens.

Your body gets warmer than usual, but you start feeling cold.

Like a heater

It all starts with you being infected by a disease. Your immune system tries to make you well again.

It is this defense that gives you a fever.

Bacteria and viruses that make you sick don't like it when it gets too hot.

Normally, the body is around 37 degrees Celsius.

But even if you get warmer, you may feel cold.

Ane Marthe Helland is a doctor and researcher at the Norwegian Air Ambulance Foundation. She studies what happens when people become very cold.

She explains why we feel cold when we have a fever.

What happens in the body is a bit like an electric heater.

If you turn up the temperature, the heater will continue to pump out heat until the room has become as warm as you wanted it to be.

A thermostat inside the heater controls this.

Your brain makes you feel cold

The same thing happens inside the brain. Here, it is the hypothalamus that controls the temperature.

When you are infected with a disease, this part of the brain decides that you will get a fever.

At first, you become warmer. But your body is still colder than what the brain has decided it should be.

That’s when you start to feel cold.

This is the brain's trick to raise the temperature in the body, Helland explains.

Shivering makes you warmer

Now two things happen.

The skin on your arms and legs becomes cold, and you begin to shiver.

In this way, the body can both retain the heat it has, and it can create more heat.

When you feel your skin getting cold, it is because the small blood vessels in your arms and legs contract, Helland explains.

This is how your body saves heat, instead of losing it through the skin.

And when you shiver, your muscles create extra heat.

In addition, you may put on more clothes or get under the covers.

Sweating when the fever is going down

The opposite happens when your fever goes down.

Then the thermostat in the brain adjusts to a lower temperature.

Your body is told that it is too hot.

You start to sweat and kick off your duvet.

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Translated by Alette Bjordal Gjellesvik.

Read the Norwegian version of this article on ung.forskning.no

Photos:

Image of the brain: SciePro / Shutterstock / NTB, photo of a mother and child with a fever: Prostock-studi / Shutterstock / NTB, photo of Ane Marthe Helland: Siftelsen Norsk Luftambulanse, photo of heater: Eldrid Borgan.