It usually all starts with a cold: you sneeze with full force and the parents startle.

For them, the sneeze is like an alarm shot, they ask worried: "Have you caught a cold again?" Then you can feel it yourself: Something is wrong in your body.

Next, the throat is scratchy, you can hardly swallow and cough.

The head is pounding, legs and arms hurt.

You feel really tired, just sick.

Johanna Kuroczik

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

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As a child, you often catch colds, especially in kindergarten.

About six to eight times a year, according to pediatricians.

And often the whole family is infected.

Other people always stay healthy.

how come

How do you catch a cold?

And what exactly is that, the snot that runs out of your nose?

At least parents know exactly how to avoid a cold.

They keep saying: put on a hat, don't go out with wet hair, where are your winter shoes?

It seems quite logical: If you're cold, you'll catch a cold.

The name already explains the connection between illness and cold: cold.

In fact, it's a bit more complicated.

Cold doesn't actually make you sick.

In the vast majority of cases, viruses are responsible, sometimes also bacteria.

These are tiny pathogens that enter our body through the nose or mouth.

They circulate particularly frequently in winter.

This is not only due to the cold, but also to the fact that in winter we spend less time outside in the fresh air and more time indoors.

When many people come together indoors, the pathogens can spread better from person to person.

You catch it when someone nearby who is already sick sneezes.

Then the viruses fly into the air, which we in turn breathe.

They end up on our mucous membranes that line our mouths and noses.

When a part of the body is particularly cold, blood flow to it becomes poorer.

You can see that on your fingers: if you forget your gloves, your fingers will turn pale and cold.

It is similar in our nose.

And if less blood flows through the mucous membranes, then fewer immune cells get there.

These are part of our so-called immune system.

Defense cells are very small and cannot be seen with the naked eye.

They protect our bodies like personal police officers.

They rush through our blood vessels, on patrol, so to speak.

They also lurk in the mucous membranes.

There they fight invaders, such as viruses.

If fewer defense cells are active, viruses have an easy time.

Then the pathogens spread by hijacking our body cells like pirates hijack other ships.

They then multiply in our body cells and soon grab the next body cell, and so it goes on and on.

This leads to something called inflammation.

Many of our symptoms are actually strategies of the body to fight the invaders.

For example fever: The brain adjusts our body temperature, just like you turn on the heating.

When it is warmer in the body, the pathogens can spread less easily and the immune system runs at full speed.

Or snot: The mucus that runs out of the nose usually consists mainly of water, so pollutants are transported out of the body.

It is produced by so-called glands.

When we're sick, they make extra slime,

to flush out the pathogens.

The lungs do the same, the phlegm from the airways is then pushed out as a cough.

If it turns green or yellow, this indicates an infection, for example that bacteria are also at work.