How extreme heat affects the body – and the best ways to cope

The heatwave that struck Europe at the end of June set a new record for high temperatures, following another unprecedented heatwave in May. A new heatwave is now underway, predicted to be even longer-lasting, with UK temperatures expected to reach up to 34°C (93°F).

To gain insight into the effects of such heat, I visited the University of Brighton’s Environmental Extremes Laboratory, situated near the Brighton and Hove Albion Football Club stadium. The lab collaborates with the club to evaluate players’ fitness. A mere 10 minutes inside a heat chamber underscored my lack of readiness for increasingly intense heatwaves, likely similar to many others.

The heat chamber is a glass-enclosed space where researchers can manipulate temperature, humidity, and oxygen levels, simulating environments like Mexico City’s elevated World Cup stadium or a European city in the grip of a heatwave.

“[Heatwaves] are here to stay, and we’ve got to help people get used to preparing for heatwaves and dealing with it, not on an off-chance, but on a regular, every-year basis, on multiple occasions,” said Neil Maxwell, the lab director, during my visit.

Maxwell and his team set the chamber’s conditions to 35°C (95°F) and 50% humidity, mirroring London’s climate during June’s heatwave. They monitored my heart rate and blood oxygen with a fingertip pulse monitor and gauged my skin temperature with an infrared thermometer, also asking me to describe my heat perception and exertion level.

Upon entering the chamber, the heat felt overwhelming, sparking some apprehension about the experience that lay ahead.

To mimic outdoor activity, I was instructed to walk on a treadmill with a slight incline. Though I began sweating, the high humidity slowed evaporation, reducing its cooling effect. In this oppressive environment, even moderate walking became challenging.

After five minutes, my skin temperature had risen from 33°C to over 36°C. Maxwell explained that my body was redirecting warm blood from my core to my skin to release heat.

My heart rate also increased from 72 to 81 beats per minute. As I lost water through sweat, my blood thickened, requiring my heart to work harder.

After ten minutes, I felt fatigued, with my heart rate reaching 95 beats per minute, and I was light-headed as Maxwell assisted me to a chair outside the chamber.

When I asked about my performance, Maxwell commented, “You’re not heat-adapted.” He noted that even healthy individuals can be susceptible.

Maxwell offered me a strawberry ice pop, which was not only delicious but also helped cool my body from the inside. Next, he had me submerge my hands in cold water. The hands, feet, and ears have dense concentrations of blood vessels, making them effective for cooling large volumes of blood.

“We get people’s temperature to drop so much quicker by using that method,” Maxwell explained.

Simple actions, like taking a cool shower—avoiding excessively cold water to prevent blood vessel constriction—can be surprisingly effective. However, Maxwell’s surveys indicate that only a small portion of the UK population takes precautionary measures against heat. He noted my lack of a water bottle despite the warm day.

Maxwell emphasized the importance of building heat tolerance over time. Aerobic activities like jogging improve the heart’s ability to pump blood to the skin. Additionally, regular heat exposure, such as sauna sessions, can train blood vessels to dilate quickly and the skin to sweat more efficiently, with less salty sweat retaining electrolytes.

“The narrative at the moment is [that] we’ve got to get rid of heat; heat is bad, bad, bad,” Maxwell stated. “I think we need to change that narrative to: safe heat can actually be therapeutic.”

After returning home, I experienced a headache and felt hot and thirsty, realizing the need to frequent the sauna more often. As for jogging, I plan to work on it.