But why are we more aggressive when it's hot?

" Don't wait until you're thirsty to drink ," " don't go out between 12 p.m. and 4 p.m. ," " close the shutters during the day "... You've certainly heard these numerous pieces of advice spread in the media or on social media as France experiences an intense heatwave.

And for good reason, heatwaves can have harmful effects on our bodies : headaches, cramps, nausea... But not only that.

Children on the front line

You may have already noticed more aggressive behavior around you, or even felt a certain aggression within yourself without being able to explain it. Don't panic, it's normal.

The German newspaper Tagesspiegel recently devoted its front page to this phenomenon: " The overheated body needs more energy to regulate body temperature, and this additional expenditure has an impact on brain function ," explains researcher Thomas Widmann of Aarhus University in the newspaper's columns .

This finding is supported by a study by researchers from the University of Grenoble who analyzed the effects of heat on a sample of 12,000 children.

The result is clear. The proportion of children exposed to average temperatures of 22°C with daily peaks exceeding 30°C during the first twenty-eight weeks of their lives had, at two years of age, a smaller vocabulary.

Bad sleep = bad day

The effects of prolonged exposure to high temperatures go further.

According to Aude Caria, psychologist and director of the public mental health information organization Psycom, quoted by Ouest-France , " sleep disorders can be caused by nighttime heat. Sleeping less well means being tired, and therefore being more irritable ."

As a direct consequence, behaviors change.

No more hateful comments online

According to the Tagesspiegel newspaper, Japanese and Korean researchers have demonstrated in a study that heat waves lead to more aggressive behavior on the road, more hateful comments on the internet and that we are " more likely than usual to feel attacked by seemingly harmless behavior ."

A 2022 study by the Potsdam Institute for Climate Impact Research confirms this work: hate speech shared on Twitter increased by 22% when the mercury exceeded 42°C.

Mental health affected

Because prolonged exposure to high temperatures directly affects our mental health.

" Links between high temperatures and an increased risk of suicide have been found, particularly in men, as well as the risk of mental health-related admissions and emergency room visits ," according to the European Climate and Health Observatory .

And according to Psychology Today magazine , citing a 2023 study by Health Science Reports, cortisol levels are directly affected during heat waves, which can " trigger stress responses, causing mood swings and agitation. The parasympathetic nervous system, responsible for calmness and relaxation, becomes less active at higher temperatures ."