A Sleep Scientist on What Extreme Heat Does to Your Brain at Night

With a massive heat dome settling over much of the eastern United States and heat index values exceeding 100 degrees Fahrenheit across the country, the public health conversation has largely focused on hydration, outdoor safety and heat exhaustion. But there is another casualty of extreme heat that does not get nearly enough attention: sleep.

Carleara Weiss, Ph.D., M.S., RN, sleep science adviser for Aeroflow Sleep, is breaking down what extreme temperatures actually do to the brain and body when we try to rest, why some of the most intuitive remedies, like a cold shower before bed, can actually make things worse, and how the longer days and shifted habits of summer quietly compound the problem even when the heat itself is not the obvious culprit. Her advice is practical and science-backed and arrives at exactly the right moment for anyone who has been staring at the ceiling, wondering why they cannot sleep.

With temperatures rising across much of the country, what happens to the body and the brain when we try to sleep in extreme heat?

Carleara Weiss, Ph.D., M.S., RN: Extreme heat directly affects brain function and whole-body metabolism, demanding a redirection of blood flow and energy from the brain to other parts of the body as the body cools itself and protects vital organs. With that, the brain (and other organs) receives less blood flow, which can make people feel sluggish and irritable and have difficulty concentrating.

Is there an ideal bedroom temperature for sleep, and what can people do to get close to it when air conditioning is not an option or is not enough?

CW: Ideally, keeping the room temperature around 68 to 70 degrees helps with falling asleep and staying asleep overnight. A fan and a bowl of ice in the sleeping room can be alternatives when air conditioning is unavailable.

A lot of people reach for a cold shower before bed during a heat wave. Does that help with sleep, or is it more complicated than that?

CW: A cold shower triggers a stress response and a rebound effect that increases body temperature rather than lowering it. It is counterintuitive; a warm shower is more effective in supporting sleep. However, I understand that a cold shower can seem inviting during a heat wave. If you must do it, make sure that the water is not extremely cold, and avoid taking it close to bedtime.

How do summer habits, like eating later, working out in the evening or spending more time in bright light, affect sleep quality during a heat wave, even when the heat itself is not the obvious culprit?

CW: Summer has a longer photoperiod, which means longer days and shorter nights. The longer days, with earlier sunrise and later sunset, delay our circadian rhythms, or biological clock. That means eating later and working out later will push our metabolism to work later, when it should be resting. In addition to this change, the extreme heat affects core body temperature, making it more challenging to fall asleep. Thus, combined, the longer days, behavioral changes, and temperature have a negative impact on sleep quality.

At what point should someone stop chalking up their sleep struggles to the heat and consider that something else might be going on, such as having sleep apnea?

CW: Someone who consistently experiences brain fog, irritability, waking up with a dry mouth or sore throat, and struggles with daytime sleepiness and fatigue, even after curbing the effects of heat, should talk to their primary care provider and consider a sleep study.