The train stops in Lübeck – and everyone wants to take their beach bags to the next crowded RE in order to travel from Hamburg to the sea on one of the last late summer days with around 30 degrees Celsius. But an argument between two women interrupts the anticipation. “Don’t push me,” calls a lady with glasses in a patterned shirt to a young woman with bell bottoms and 90s sunglasses who hurries past.

And before she knows it, the young woman receives a loud slap in the face. The rest of the passengers are dismayed. A man from DB security checks that everything is going well and the women part, cursing, without further outbreaks of violence. And on the way to the Bay of Lübeck I’m left with the question of whether the heat isn’t just literally going to people’s heads.

It quickly becomes clear that the phenomenon has a name: “Long Hot Summer Effect”. He describes the fact that people behave more aggressively at high temperatures and are more easily irritable. The scientists Paul A. Bell and Robert A. Baron investigated the phenomenon of heat and aggression in an experiment in the 1970s. They divided 64 male students into two groups. One group was allowed to criticize the other. The other was allowed to punish her with electric shocks. And: The hotter it was in the test room, the more often the students gave their critics electric shocks.

The influence of heat on behavior is broad: An analysis of temperatures and penalties in professional football (National Football League in the USA) showed that the hotter it was, the more players committed rule violations. The home team in particular tended to behave aggressively. The researchers therefore assume that, in addition to the heat, the fans present could also play a role. The heat also seems to have an effect on drivers in traffic: researchers conducted an experiment in the 1980s. Research staff “missed” the green traffic light. On hot days, the displeasure of waiting drivers was particularly great: it ended in particularly loud honking. Those who didn’t have air conditioning in their car honked the horn most often.

In addition to these rather harmless consequences, heat also seems to have more drastic effects: A longitudinal study from the USA over a period of 45 years came to the conclusion that violent attacks increase in warm years and seasons. On the other hand, researchers concluded in a study that people are less helpful in high temperatures. The US scientist Craig Anderson showed in a study more than 20 years ago that more violent and sexual crimes are committed during heat waves. A recent study from 2021 even found that violence among inmates in prisons increases by 18 percent on very hot days.

However, due to their design, the results of such experiments and studies can only ever be viewed as an indication of a connection. So you can’t prove that the increased aggressiveness in heat is actually due to this. The researchers cannot rule out that other factors, such as more people spending time outdoors or more alcohol consumption, also play a role.

One thing is certain: heat has a direct effect on our body. In addition to the obvious fact that the body increases sweat production in hot weather so that the body temperature does not get too high, the blood vessels also dilate. This lowers blood pressure, explained Florian Heindl, chief physician in the emergency room at the Helios clinics in Munich West and Munich Perlach. The heart responds by increasing its pumping capacity. Heat can therefore act as a stressor on us.

For Central Europeans, the comfortable temperature is around 22 to 25 degrees Celsius, Professor Hanns-Christian Gunga told “Deutschlandfunk Nova”. He set up the Center for Space Medicine and Extreme Environments at the Berlin Charité. If the thermometer climbs to 30 degrees or more, this is too much for Central Europeans. A possible explanation for the aggressive behavior in heat is the hormone vasopressin, which regulates water balance and is increasingly released by the body at high temperatures. Because: The body tries to store as much liquid as possible and therefore releases more of the hormone. This not only affects the water balance, the hormone also increases our aggressiveness.

There could also be a very simple explanation for why the warm weather drives us so crazy: We quickly become irritated when we feel unwell. Heat can also make us feel uncomfortable, stressed and irritable. Among other things, through: increased sweating, poor sleep, tiredness and reduced comprehension.

Environmental researcher Solomon Hsiang suspects that when weather conditions are stressful, people tend to misunderstand ambiguous situations, which can lead to more misunderstandings and conflicts.

In addition to aggression, heat can also lead to more restlessness and anxiety. “During a heat wave, there is a significant increase in stress, anxiety and depression, especially among older and weaker people, but also among younger people who lack fitness. The prospect of not being able to escape this heat leads to psychological distress Problems that should not be underestimated,” explains Hans-Peter Hutter, environmental medicine specialist from MedUni Vienna, in a statement. This could lead to, among other things, panic attacks.

A study from the USA and Mexico even came to the conclusion that the risk of suicide is increased on hot days.

Do you have suicidal thoughts? Telephone counseling offers help. It is anonymous, free and available 24 hours a day on (0800) 1110111 and (0800) 1110222. Advice via email is also possible. A list of nationwide help centers can be found on the website of the German Society for Suicide Prevention.