by Josh Forman, Head of Science, Education & Outreach
Heatwaves: Love them or loath them? It’s in your DNA.
The UK is getting hotter. Our summers now regularly include days over 30ºC (Met Office, 2025), something we didn’t see as often in the past. But the question is: how do you respond to it?
Why do we all respond so differently to heat? And why does our relationship with it change over time?
I’m not talking here about broad, long term genetic differences between populations, although those are real and rooted in evolutionary biology. One of the clearest examples of this is how body shape has adapted to climate over generations. People from traditionally hot climates, like parts of Africa and Southeast Asia, often have leaner builds and longer limbs. This increases surface area relative to body mass, which helps the body lose heat more efficiently. In contrast, populations from colder climates, such as Inuit communities or northern Europeans, tend to have stockier builds and shorter limbs, which help them retain heat by reducing surface area.
This follows two biological principles: Bergmann’s Rule, which suggests that animals including humans in cold climates tend to have more compact bodies, and Allen’s Rule, which observes that warmer climate populations tend to have longer limbs to aid heat dissipation. These differences aren’t just cultural, they’re physical adaptations to the environment, shaped over many generations.
But beyond these inherited traits, what about within individuals? Why do some people feel completely at ease in a heatwave while others wilt?
Let’s start with a fundamental question: why does the body need to regulate its temperature in the first place?
We aim to keep our bodies around 37ºC because that’s the optimal temperature for our enzymes, the proteins that control every chemical reaction in the body. Enzymes need heat energy to function, but if the body gets too hot, the bonds that maintain their precise shape can break down, stopping them from working. So 37ºC is a kind of sweet spot, warm enough for activity but not so hot that things start to unravel – plus it gives us a little buffer before the real damage can be done.
When our body overheats, it kicks in with thermoregulation, a form of homeostasis you may remember from GCSE biology. Thermoreceptors in the skin and blood vessels detect temperature changes and send messages to the hypothalamus, the brain’s internal control centre. This triggers a range of responses, such as sweating and vasodilation, where blood vessels widen to move warm blood closer to the skin. This helps release heat from the body, often leaving us looking flushed.
But even with these mechanisms in place, some people just seem to cope with the heat better than others because we have different levels of thermoregulatory response. Some people have a more effective response than others.
One explanation is a process called heat acclimatization, which we believe is influenced by epigenetics, a system that controls how genes are expressed without changing the underlying DNA sequence.
Epigenetics acts like a dimmer switch for genes. It can turn them on (expression), off (silence), or adjust their activity. Environmental factors, like regular exposure to heat, can cause these switches to flip. This means that over time, the body can learn to deal with heat more effectively (or less effectively if not exposed to heat). Crucially, these are reversible changes that happen within a person’s lifetime, not permanent genetic mutations.
A clear example of this is how our sweat response adapts. With repeated heat exposure, people start sweating earlier, sweat more, and their sweat becomes more dilute, meaning less salt is lost. This helps cool the body more efficiently while conserving important electrolytes. These changes usually take one to two weeks to develop and show how the body can fine tune itself to suit its environment (Murray, 2023).
Interestingly, once you’ve adapted, the body seems to remember. You’ll reacclimatize more quickly the next time you’re exposed to similar heat, whether it’s a summer heatwave or your next holiday abroad.
We know this from studies on heat shock, short intense bursts of heat that trigger dramatic epigenetic changes (Casali, 2024). These changes are designed to be temporary, but they show how our biology is built to adapt quickly to temperature changes. It’s likely that longer term exposure to moderate heat also triggers more subtle, longer lasting changes that help us cope.
In short, yes, you can train your body to handle heat better. And beyond the biology, there’s probably a significant psychological element too. Some people simply enjoy feeling warm, while others find it draining. Whether that’s nature, nurture or habit, it’s another reminder that our relationship with temperature is deeply personal.
