How to sleep when it's hot outside

As January draws to a close, we have seen sweltering conditions across the country. According to MetService, last week, temperatures approached 40℃ in parts of the South Island, and exceded 30℃ in some North Island regions. Most of us have endured the discomfort of trying to sleep on an unbearably hot night. Thankfully, there are things you can do to maintain a comfortable temperature all night long.

Temperature and sleep.

Although light is the primary signal used by our bodies to synchronise our circadian rhythm, temperature also plays a role. This makes sense from an evolutionary perspective: just as light levels oscillate between light and dark, the air temperature fluctuates between higher temperatures during the day and cooler temperatures as the sun sets. As such, our body is designed to experience a slight dip in core temperature during the evening. That's why the ideal temperature for sleep, 15.6 to 19.4℃, is slightly cooler than you might expect. As we have seen this week, the summer weather can often bring the temperature well above this range, interfering with the bodies thermoregulatory process.

How to sleep on a hot night

  • Close your bedroom's curtains during the day, to reflect some of the suns heat.
  • Take a hot bath or shower: This sounds counter-intuitive but bear with me. The hot-water enhances vasodilation (the process by which the body naturally drops in temperature), drawing blood away from the core out to your extremities. As you exit the shower (or bath), water evaporates from your skin, which draws heat away from the body. This, combined with the fact that warm water enhances relaxation, means that it deserves to be a part of your bedtime routine.
  • If you have air conditioning, set your thermostat to somewhere between 15.6 to 19.4℃.
  • Use a bedside fan, to increase air circulation and help you stay cool.

We hope these tips help you sleep throughout the warmer months.


Haghayegh, Shahab, Khoshnevis, Sepideh, Smolensky, Michael H, Diller, Kenneth R, & Castriotta, Richard J. (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews, 46, 124-135.

Okamoto-Mizuno, Kazue, & Mizuno, Koh. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1), 14.

Harding, Edward C, Franks, Nicholas P, & Wisden, William. (2019). The Temperature Dependence of Sleep. Frontiers in Neuroscience, 13, 336.

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