Hot baths before bed during a heat wave can improve sleep, studies show

You may be used to cooling off with a quick cold shower or staying hydrated with cold drinks during the summer heat. However, when the temperatures rise, it may seem backwards to be advised to take a hot bath – but there is a scientific reason behind this seemingly strange advice.

Healthline reports that a study found that a hot bath about 90 minutes before bed could help people fall asleep faster. It may seem strange to dive into hot water when it’s scorching outside, but there’s science to back it up.

The research was conducted by Shahab Haghayegh, a PhD candidate in the biomedical engineering department at the University of Texas at Austin. The team conducted a systematic review of data evaluating research linking bathing, water temperature and sleep quality.

They examined 5,322 studies and used about a dozen with robust methodologies to draw their conclusions. Their results suggest that taking a bath one to two hours—ideally, 90 minutes—before bed in water at 104 to 109F (40 to 43C) can help people achieve optimal sleep quality.

Bathing at that particular time and temperature can help you fall asleep an average of 10 minutes faster than usual.

Another study published in the journal Sleep Medical Reviews showed that both sleep and core body temperature are regulated by the brain’s circadian clock, which controls our 24-hour sleep-wake cycle. Our body temperature is at its lowest when we sleep, and a drop in body temperature after a bath can help prepare us for sleep.

However, taking a cold bath or shower before bed could have the opposite effect, leading to a restless night. Research by the Sleep Foundation found that cold showers may not improve sleep due to the stimulating properties of cold water, which increase cortisol and norepinephrine levels in the body.

Cortisol plays a role in increasing alertness, and usually cortisol levels in the body decrease in preparation for sleep. In one study, participants compared the energy boost from a cold shower to the effects of caffeine consumption.