You’ve just left the house and feel like you’ve forgotten something (it’s putting on shoes. You’re still wearing your slippers). You’re on the bus and have re-read the same paragraph of your book five times – the information just isn't going in. Every meeting feels more boring than usual. You’re asked for your thoughts and find you can’t string a sentence together.
In short, it feels like your brain is melting in the heat. Your memory sucks, your thoughts are slow, and your fuse is shorter than usual. You’re off your game.
You’re not imagining it. And it’s not down to any personal failing – the heatwave is likely to blame.
The hot weather really can impact your cognitive skills, impacting everything from your ability to make decisions to how tired you feel. But why? And what can we do about it? Ahead, neuroscientists break down how the heat affects your brain – and share their top tips for counteracting the impact.
How and why hot weather affects your brain
‘The brain is much less capable in the heat,’ Natalie Mackenzie, a brain and cognition expert with 20 years of experience in neuropsychology, tells Good Housekeeping. ‘Most people don’t realise quite how directly temperature affects cognitive function.’
The reason for this is simple: when it’s hot, your brain and body both have to work hard to cool down, depleting the energy you have for anything else. Rachel Lambert, the founder of Braincode Centers, explains: ‘Heat doesn't just make you uncomfortable; it actively competes with your brain for resources. The brain is the most metabolically expensive organ in the body, consuming roughly 20% of your total energy despite being only 2% of your body weight. When core temperature rises, the body redirects blood flow toward the skin and periphery to dissipate heat. That's a survival priority, but it comes at a direct cost to cerebral blood flow and the glucose and oxygen delivery the brain depends on for sharp thinking. What you experience as sluggishness, difficulty concentrating, or unusual irritability in a heatwave is your brain operating on a reduced budget.’
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Lots of things we’d usually be great at can go a bit dodgy when temperatures rise. You might typically have immense patience, but suddenly get irritated by the slightest queue for an iced coffee. Perhaps a work task that’s usually a breeze feels loads harder. ‘Hot weather can make tasks that involve demanding thinking more difficult,’ says Volker Thoma, a professor of cognitive psychology at the University of East London. ‘The cognitive functions most consistently affected are sustained attention (e.g. driving), working memory (anything to do with remembering information or procedures), response control (resisting urges, such as checking your mobile or online gambling), and maybe even complex decision-making.
'The reason for this is at least twofold: 1) you notice more bodily signals (e.g. that you are thirsty), which is distracting; 2) because of dehydration, parts of your brain may not function as well (such as the so-called nucleus accumbens, responsible for cognitive control), and in general the usual nutrients and oxygen are not delivered (perfusion) as well as usual throughout brain tissue. In short, you are more error prone, from little kitchen mishaps to errors at work.’
There’s research to back this up. Studies of firefighters and miners suggest that heat exposure can reduce vigilance, slow down reaction times, and make it harder to hold information in mind. In another study in 2018, young adults living without air conditioning performed more slowly on tests of selective attention and processing speed and showed poorer working-memory performance than those in air-conditioned accommodation.
Stress makes all this worse… and the heat makes you more stressed. ‘At the most basic level, when we're hot and can't do anything about it, we're stressed and distracted, so our brain has more to think about and deal with, reducing our ability to focus on other things,’ says Dr Dean Burnett, a neuroscientist and the author of The Idiot Brain and Psycho-Logical. Fun! Stress begets stress. Rachel highlights a brutal cycle: ‘Thermal stress activates the same hypothalamic-pituitary-adrenal axis that psychological stress does. Sustained heat exposure is a low-grade stress response running in the background all day.'
On top of all that, there’s the mental impact of other hot weather consequences. It’s hard to sleep in the heat, and a bad night’s sleep exacerbates all cognitive struggles. Volker notes: ‘Disrupted sleep can impair attention and judgment the next day. Higher overnight temperatures have been linked with greater impatience and more violations of rational-choice principles. Older adults may be particularly vulnerable, with heatwaves associated with poorer memory and visuospatial performance.’
‘The sleep problems from unsettled sweaty nights compounds everything,’ agrees Natalie. ‘The brain needs core body temperature to drop to get into deep, restorative sleep. Heat prevents this, so cognitive fog during a heatwave tends to get progressively worse across days as sleep debt quietly accumulates on top of the direct effects of heat.’
All in all… it’s bad news for our brains when the temperatures hit I-urgently-need-an-ice-cream levels. But good news is that there are things you can do.
Neuroscientists’ top tips for dealing with the hot weather’s impact on your brain
Prioritise sleep
‘The main tip I would give (other than of course stay hydrated): Make sure you sleep well during the hot weather,’ says Volker. ‘A cool bedroom, light bedding and good ventilation can protect sleep (in addition of course to good bedtime routines, restricting alcohol consumptions, and so on). This in turn is important to be prepared for tasks requiring attention, working memory and decision-making the next day when these functions are under heat attack again.’
Drink plenty of water
Staying hydrated is always important, but it’s absolutely vital in a heatwave. And not just for your body, but for your brain, too. Professor Peter McNaughton, a researcher at Kings College London, tells us: ‘Hot weather causes dehydration that reduces blood volume and thus causes a drop in blood pressure. Lower blood pressure means less oxygen to the brain – meaning poor decision-making and possible unconsciousness.’
Restructure your day
‘Try to adjust your working routine,’ suggests Natalie. ‘More cognitively challenging things in the cooler morning hours, no big decisions in the afternoon.’
Rachel seconds this: 'My tip is to protect your first two hours of the day before the heat peaks and cortisol levels rise. Do your most cognitively demanding work then. Treat the cool morning window as a non-negotiable cognitive asset, not just a comfort preference. The brain you have at 7am in a heatwave is genuinely a different brain to the one you have at 2pm. Plan accordingly.'
Hydrate before you feel thirsty
‘Thirst is often a sign that mild dehydration has already begun, and even small fluid losses can affect concentration, memory and mood,’ advises Puravi Joshi, the neuroscience-informed founder of NAAVA. ‘Rather than drinking large amounts at once, aim to sip water regularly throughout the day. If you're spending long periods outdoors or sweating heavily, replacing electrolytes can also help.
‘We often think of hydration as something we do for our bodies, but it's equally important for keeping our brains calm, focused and functioning at their best. Think of hydration as brain fuel: when temperatures rise, your brain needs it just as much as your body.’
Take it easy
Dean notes that sometimes feeling tired and drowsy when it’s hot is your brain telling you to slow down. ‘I think the best advice is, listen to what your brain and body are telling you,’ he says. ‘We in the UK have essentially been conditioned to appreciate the hot weather because it's so rare for us (we pay thousands every year to go elsewhere and find it!), so we all feel we should 'make the most of it' when we get it. I've seen so many people out and about during the heat and clearly not enjoying it. You don't need to do that. If you're too hot, you're too hot, so stay in, close the curtains, get the frozen peas on your head, whatever it takes. Being too hot is a matter of physics, not laziness. It's fine to acknowledge that.’
