Your brain at 45°C: Why heat makes you moody, distracted and forgetful — and what to do about it

You probably know the feeling: asking someone to repeat something simple, not because you're distracted, but because your brain just isn't keeping up. No, you’re not dim, it could just be the unbearable heat muddling your thoughts.

The truth is, your brain is reacting to heat stress. So, you walk out of a scorching commute and forget what you had to do. You snap at a co-worker for no reason.

As Dr. Eleni Margioti, Neuropsychology Lead at The Brain & Performance Centre, explains, when temperatures soar, the body works overtime to regulate itself. Yet, that effort, coupled with dehydration, disrupted sleep and too much sun exposure, chips away at the cognitive performance. “Thinking becomes slower, moods more unstable, and focus harder to maintain,” says Dr. Margioti. And while anyone can feel the effects, she warns that children, older adults, and those with pre-existing conditions are even more vulnerable.

Scientists are still piecing together exactly why heat messes with our mood and mental clarity, but several compelling theories have emerged. One widely supported idea:Your brain is just too busy trying to keep you cool.

“When the body overheats, blood flow gets redirected to the skin to help cool it down,” explains Dr Margioti. “That means less oxygen and fewer nutrients are reaching your brain.” Throw in even mild dehydration, and suddenly you’re struggling to form a sentence or remember what you walked into the kitchen for.

When vital resources like glucose and blood are being diverted to thermoregulation, less energy is left for the brain regions that handle higher-level functions like memory, focus, and decision-making. This becomes especially clear under prolonged heat exposure.

For instance, in a 2020 study titled Heat and Learning, US.-based researchers (as cited by The New York Times) found that students performed worse on standardised tests during school years with a higher number of hotter-than-average days—particularly when temperatures rose above 80°F (27°C). The researchers believe heat exposure over time affects learning and cognitive function, not just momentarily but cumulatively.

If you’ve ever snapped at a colleague or felt unreasonably annoyed during a hot afternoon, that’s not just bad temper—it’s your brain under stress. “When the body overheats, it diverts blood flow to the skin to cool down, leaving less oxygen and energy for the brain, particularly the prefrontal cortex, which is responsible for impulse control and emotional regulation,” explains Dr Margioti.

A 2021 study published in The Lancet Planetary Health backs this up, finding a strong correlation between hotter days and increased rates of mood disturbances, including anxiety, irritability, and even aggression. So yes—your short temper might literally be heat-induced.

Even more concerning is that the effect of heat on the brain isn’t just cumulative—it can happen almost immediately. A 2024 study published in Ecotoxicology and Environmental Safety tracked over 53,000 people for eight years and found that extreme temperatures were associated with reduced cognitive performance not just over years or days—but by the hour.

What’s happening? During heat stress, brain support cells like microglia and astrocytes go into overdrive, releasing inflammatory substances. This inflammation can damage neurons and impair the formation of new ones, affecting memory, focus, and overall cognitive clarity.

So, how do you give your brain a break when the weather won’t? Dr. Margioti offers a few easy but powerful strategies to keep your mental edge sharp:

Drink before you think
“Hydration isn’t just for workouts—it’s essential for brain function,” says Dr. Margioti. Start your day with water and sip throughout, especially if you’re spending time outdoors or in overly air-conditioned spaces. And don’t wait to feel thirst.

Chill your space
Even a small drop in temperature can make a noticeable difference in mental clarity. Pull those blackout curtains, use a fan, and skip heat-generating appliances. “If you're on the move,” says Dr. Margioti, “Take regular breaks in shaded or air-conditioned areas.”

Rescue your sleep
Quality sleep is your brain’s overnight detox. “Aim for a cool, dark sleep environment,” she advises. Ditch heavy bedding, shut down screens an hour before bed, and take a quick cold shower to lower your core temperature. “Quality sleep acts like a nightly reset for your brain.”

Exercise your mind.
Mental workouts matter. “Mental stimulation builds cognitive resilience,” says Dr. Margioti. Even 10 minutes a day spent reading, solving puzzles, or learning something new can help counteract summer brain fog.

And while most of us can tell when we’re overheated, children seniors, and those with neurological conditions may not be able to verbalise their discomfort. “Children, older adults, and people with neurological conditions may show more subtle signs, such as confusion or irritability,” says Dr. Margioti. “That’s why hydration, rest, and staying cool should be non-negotiable.”

In a country where summer feels like a second full-time job, it’s easy to overlook the mental cost of enduring endless heat. But your brain: It’s quietly doing its best to cope. So this season, don’t just slather on sunscreen—“Protect your clarity and focus with hydration, rest, and a little planning,” says Dr. Margioti.