Why extreme heat makes people angrier and how our brain reacts to heatwaves

With extreme temperatures ramping up across Europe, not everyone faces them in the same way.

Heat and sun exposure have well-known effects on health, ranging from dehydration to skin rashes and burns.

However, a lesser-known effect of heat on the body has to do with mental health.

“Research shows that on hotter days, rates of aggression, road rage, violence, and even emergency room visits for mental health concerns tend to increase,” Susan Albers, a clinical psychologist at the Cleveland Clinic, told Euronews Health.

So, what is driving these behaviours and changes in mental health?

Coping with constant discomfort

Being overheated makes us uncomfortable. “When we're physically uncomfortable, we have less patience, we're more irritable, and we're quicker to react emotionally,” said Albers.

She noted that when the brain is working overtime and under heat stress to keep the body cool, it leaves fewer resources for staying calm and focused.

The key thing during periods of high temperatures is to stay hydrated. Health experts repeat the mantra of how important it is to drink enough liquids, one cup of water per hour and at least two to three litres per day, according to the World Health Organization.

A dehydrated body loses its ability to regulate its temperature and can cause sleepiness, dizziness and headaches. It can also impact the way the brain works.

“Even mild dehydration can affect the parts of the brain responsible for attention, decision-making, and emotion. You may feel more anxious, foggy, or irritable before you even realize you're thirsty,” said Albers.

Some easy solutions include drinking something cold or using a cold cloth or ice pack to cool the parts of your body with blood vessels closer to the skin such as the neck, wrists and ankles.

“Overheating can make your brain feel overstimulated. If you notice yourself becoming irritable, anxious, or overwhelmed, change your environment,” recommended Albers.

The importance of a good night's sleep

Sleep plays a major role in the correct functioning of the body during the day.

One characteristic of heatwaves is tropical nights — defined as when the temperature overnight does not fall below 20°C. While this is more common in warmer climates, cooler countries are experiencing them more frequently.

Nighttime is when the body is supposed to recover. When the temperature does not cool off during the night, this recovery does not happen and the body remains under strain.

When we sleep, our core temperature drops, our cardiovascular system rests, and the cumulative stress of a hot day begins to ease, said Armel Castellan, extreme heat services technical advisor at the World Meteorological Organization and the WHO.

Sanders also identified a poor night's sleep as a trigger for mood changes and emotional dysregulation.

“Even one bad night's sleep can make you more emotionally reactive, impatient, and less able to cope with everyday frustrations,” she noted.

People with mental health conditions are more vulnerable

People with existing mental health conditions are also more sensitive to extreme heat.

Previous research has found that it can have both immediate and lagged effects, including increased risk of suicide, schizophrenia symptoms, anxiety, depressive and substance use disorders.

“People with anxiety may notice the heat more because many of the physical sensations of being overheated like a racing heart, sweating, and shortness of breath, feel similar to anxiety, which can create a cycle where each makes the other worse,” said Albers.

She also noted that certain medications, including some antidepressants, stimulants, antihistamines and blood pressure drugs, can make it harder for the body to cool itself or increase the risk of dehydration.

Some treatments may also become less effective or increase the risk of side effects when the body becomes overheated or dehydrated.