'Like a boiling egg': How the heatwave affects your body

'Like a boiling egg': How the heatwave affects your body
It is crucial to keep cool and stay hydrated during a heatwave. Credit: Canva

With the heatwave that has already caused severe problems in Southern Europe arriving in Brussels, the next few days will be extremely hot. In such weather, the death rate is often higher than average. But what does heat do to the body and how can it become fatal?

In 2020, a heatwave swept over Belgium in August, during and after which the public health authority Sciensano recorded a mortality rate of nearly 35% (1,460 deaths). This was well above the average death rate that year of 9.8%.

How heat strokes happen

While over-65s are the main age group affected, heat strokes can happen to anyone. Heat strokes are brought on by high ambient temperatures or when physical exertion increases the body temperature. In combination, this can be dangerous.

When the body gets heated, the blood flow to the skin is increased and blood vessels expand. Sweating cools down the body as sweat evaporates and draws heat from the body.

As long as the outside temperature is lower than your body temperature, you can transfer heat into the cooler environment. But if the temperature rises above 37°C, this is no longer possible. The body starts to rely exclusively on sweating.

Getting rid of excessive heat becomes even more difficult when high temperatures are accompanied by high humidity, as sweat evaporates less easily.


When the blood vessels dilate, blood pressure drops, meaning the heart has to work harder to pump blood around the body. That can be done by the heart beating more quickly or by pumping more blood with each stroke.

“The elderly and people with an underlying heart condition find this harder and are therefore more vulnerable to overheating,” emergency physician Cathelijne Lyphout told De Morgen.

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If your body temperature rises above 40°C, body functions start to slow down. Proteins involved in crucial processes work less well. “At higher temperatures, their structure can change, similar to when you boil an egg,” said Lyphout.

Enlarging brain

The walls of cells can rupture, causing leaks. “When the contents of cells of the gastrointestinal tract leak, this can lead to an excessive reaction of the immune system,” said emergency physician Sandra Verelst.

With more blood flowing to the skin, less blood flows to vital organs. Clots can form in small blood vessels, or they can burst. “All these processes together can lead to a reduced functioning of the heart, kidneys and other organs, and ultimately even to multi-organ failure,” Verelst explained.

In addition, the brain also warms up when the core temperature rises. The brains therefore expand, but there is limited space in our skull. “This reduces blood flow to the brain,” said Verelst. “That too can be fatal.”

To avoid coming to harm, it is crucial to cool down and slow down at the first symptoms of overheating – such as dizziness, nausea, faster breathing and heart rate.

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