Hot Nights Disrupt Sleep and Reduce Next-day Restfulness

One reason is thermoregulation, the body's ability to keep its internal temperature within a safe range. Sleep is closely linked to body temperature: to fall asleep and stay asleep, the body usually needs to lose some heat. Hot bedrooms make that harder.

And UK summers are becoming hotter. The Met Office has reported that the chance of exceeding 40°C in the UK is now more than 20 times higher than it was in the 1960s, with a 50% chance of another 40°C day in the next 12 years. Humidity can make the problem worse.

Research on humidity and heat stress shows that high humidity can increase the strain heat places on the body. The body cools itself partly by sweating. As sweat evaporates from the skin, it carries heat away.

But when the air is already humid, evaporation becomes less efficient. So how can you sleep better in hot weather? Air conditioning is one answer, but it is not affordable or practical for many households.