Too Hot to Sleep? Your AC May Be Making Things Worse

We all know how difficult it can be to fall asleep when it's too warm. But could seeking relief with an air conditioner cause more harm than good?

by Martin Reed Patient Advocate

We all know just how difficult it can be to fall asleep in the hot, sweaty days of summer. Most seek relief with an air conditioner. But could this convenience be causing more harm than good?

Although previous research found that very high and very low temperatures decrease the amount of deep sleep we get and increase the frequency and duration of nighttime awakenings, the effect of temperature on sleep is less well-known compared to other external influences such as light exposure.

A study published in the journal Building and Environment set out to investigate how our sleep is affected by specific air temperatures and the cooling routines of air conditioners.

The study involved 18 healthy individuals (nine men and nine women) with an average age of 23. Each participant slept in a temperature-controlled chamber for four nights.

Researchers investigated the effects of the following temperature cycles on sleep:

  • A constant temperature of 79°F (26°C)

  • A fall-rise temperature change of 82°F (28°C), 81°F (27°C), 79°F (26°C), 81°F (27°C), 82°F (28°C)

  • A rise-fall temperature change of 77°F (25°C), 79°F (26°C), 81°F (27°C), 82°F (28°C), 81°F (27°C), 79°F (26°C)

Participants in the rise-fall temperature condition reported poorer sleep quality and fewer felt they got enough sleep compared to those in the other temperature conditions. This suggests thata slow rise followed by a slow fall in temperature can have a negative impact on sleep.

Unnatural temperature changes Our core body temperature naturally falls from early in the evening through to the middle of the night. It then begins to slowly rise as morning approaches. This negative effect, therefore, could be tied to the fact that a rise-fall temperature change is the exact opposite to how our body naturally behaves during a regular sleep cycle.

Those who slept in the constant and rise-fall temperature condition also reported feeling less comfortable during and after sleep compared to those in the fall-rise temperature condition.

After using polysomnographic data to obtain objective data, researchers confirmed that those in the rise-fall temperature group took the longest to fall asleep.

Cool Versus Warm Sleeping Environments

When looking at all the data, researchers found that a comfortably cool environment made it more difficult to fall asleep compared to a comfortably warm environment.

Researchers think this is because we typically fall asleep faster when our blood vessels dilate to keep us cool in the evening. If our sleeping environment is warmer, our blood vessels do not dilate as much, which can delay sleep onset.

How to Set Your Air Conditioner for the Best Summertime Sleep

When it comes to cooling your room at night, it may be best to avoid running the air conditioner too early in the evening. This will prevent the room from becoming too cool when it's time for bed.

Our bodies prefer to sleep when the temperature is elevated and drops slowly through the first half of the night. If you're able to program your air conditioner to slowly reduce the temperature over the first half of the night and then slowly increase in the second half of the night, you'll be giving your body the perfect thermal conditions for sleep.

The alternative option would be to keep your bedroom at a constant temperature throughout the night -- participants who slept at a constant temperature saw similar results to those who slept in the fall-rise condition when it came to sleep quality and thermal comfort during sleep.

If you choose this option, it's important to make sure the room isn't too cool, though.

A comfortably warm environment of between 79°F (26°C) and 82°F (28°C) appears to be more appropriate than a comfortably cool environment of around 77°F (25°C).

Finally, don't be tempted to assume that a few degrees is insignificant. Previous research found that a temperature change of just 2.7°F (1.5°C) has a huge influence on our core temperature during sleep.

Martin Reed
Meet Our Writer
Martin Reed

Martin is the creator of Insomnia Coach, an eight-week course that combines online sleep education with individual sleep coaching. His course helps clients improve their sleep so they can enjoy a better life with more energy and start each day feeling happy, healthy, rested, and refreshed. Martin also runs a free sleep training course that has helped over 5,000 insomniacs. He holds a master’s degree in health and wellness education and studied clinical sleep health at the University of Delaware.