Expert voices: How to beat brain fog during a heatwave
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Expert voices: How to beat brain fog during a heatwave
Published 25 June 2026
By Volker Thoma, Professor of Cognitive Psychology at the University of East London
As the UK swelters under an intense heatwave with temperatures expected to reach almost 40C, many of us are finding it impossible to focus on even simple tasks. While we easily spot the physical toll of extreme heat - sweat, sunburn and exhaustion - we may overlook what it is doing to our minds. Here’s why hot weather can drain your brainpower, and what the science says about how to protect it.
Professor of Cognitive Psychology
How heat hijacks your cognitive functions
Hot weather can make tasks that involve demanding thinking significantly harder. Because the body is working overtime to regulate its temperature, we often experience a mix of thirst, fatigue, discomfort and dehydration. The cognitive functions most consistently affected are sustained attention, working memory (which includes retaining information or procedures), response control (including resisting urges, such as checking your phone), and complex decision-making.
The reason for this “brain drain” is twofold: the brain gets crowded by physical signals, and you may notice more bodily sensations like thirst and sweating, which are highly distracting; dehydration alters brain function, meaning parts of your brain responsible for cognitive control, like the nucleus accumbens, don't perform as well. Dehydration reduces blood flow (known as perfusion) meaning crucial nutrients and oxygen aren't delivered efficiently throughout brain tissue.
In short, you become far more error-prone, leading to everything from little kitchen mishaps to critical mistakes at work.
From extreme professions to everyday settings
Research in physically demanding occupations demonstrates these effects. Studies of firefighters and miners suggest that acute heat exposure reduces vigilance, slows reaction times, and hampers the ability to hold information in mind or inhibit automatic responses). These abilities are critical when people must remain focused and make accurate decisions under pressure.
But this isn't just a risk for extreme professions; the effects are just as evident in everyday settings. During a previous summer heatwave, young adults living without air conditioning performed significantly more slowly on tests of selective attention and processing speed, while showing poorer working-memory performance, than those in air-conditioned accommodation.
The science of hydration and brainpower
Dehydration is a massive contributor to these problems. In 2019, we found that drinking water after overnight fluid restriction immediately improved performance on judgment and decision-making tasks. Crucially, this improvement wasn't just about quenching the psychological feeling of thirst; biological tests confirmed it was tied directly to physiological hydration levels. Although the study did not test heat directly, it suggests that maintaining hydration is a vital shield for reflective thinking during hot weather.
The hidden dangers of a hot night
Hot nights present another hidden danger, because disrupted sleep further impairs attention and judgment the next day. Higher overnight temperatures have been linked with increased impatience and a breakdown in logical decision-making. Older adults are particularly vulnerable, with heatwaves directly associated with poorer memory and visuospatial performance in older adults.
Overall, heat reduces the mental resources available for concentration, memory and careful decision-making – particularly when exposure is prolonged, sleep is disrupted or hydration is inadequate.
How to protect your brain
Beyond the obvious advice to stay hydrated, the single best thing you can do is protect your sleep. A cool bedroom, light bedding and good ventilation are non-negotiable to safeguard your rest. Combine this with a solid bedtime routine and limiting alcohol, which worsens both dehydration and sleep quality. Protecting your night is your best defence to ensure your brain can survive the heat the next day.
Professor Volker Thoma is available for interview. Please contact pressoffice@uel.ac.uk to arrange.
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