Take a 10-minute warm shower before bed

Why your body cools down for sleep

Your body runs on an internal clock that also sets your temperature. During the day, your core temperature, the warmth deep inside your body, stays slightly higher. In the evening, it starts to fall by a fraction of a degree. Sleep tends to begin while this drop is under way, so anything that helps it along may make falling asleep a little easier.

How warm water helps you cool

It sounds backwards that warming up would help you cool down. Your body sheds most of its heat through the skin, especially your hands and feet. Warm water widens the blood vessels near the surface, so more warm blood flows from your core to your skin. When you step out into a cooler room, that heat leaves your body, and your core temperature can drop faster than it would on its own.

Researchers in Switzerland measured part of this directly. In a small lab study published in Nature, the gap between warm hands and feet and a cooler core was the best predictor of how fast people fell asleep. Warm hands and feet seem to be one of the ways the body gets ready for sleep.

What the research found

In 2019, a team at the University of Texas reviewed the studies on warm showers and baths before bed and pooled the results of 13 of them. Water between 40 and 42.5°C (104 to 108.5°F) was linked to better self-rated sleep quality. It was also linked to better sleep efficiency, which means spending more of your time in bed actually asleep. When people finished the warm water one to two hours before bed, they fell asleep about 10 minutes faster on average. Sessions as short as about 10 minutes were enough to show the effect.

The effect is real but modest, and the studies have limits. Most were small, the people studied ranged from young adults to older adults, and the methods varied a lot. Researchers still don't know which temperature and timing suit which people best. The studies point to comfortably warm water, so there is no reason to go hotter or stay in longer. Nothing in the research suggests a nightly shower is too much, so you can do it every evening.

Fitting it into your evening

Give the shower a fixed place by tying it to a moment that already happens about 90 minutes before bed, such as clearing away dinner. If you go to bed at 11 p.m., that means stepping into the shower around 9:30 p.m. Keep the water comfortably warm, enough to turn your skin a little pink without making you sweat or feel lightheaded. If you share a bathroom, claiming it right after dinner also means less queueing at bedtime, and fewer polite knocks on the door. If you only get to it right before bed, keep it brief and not too hot, because the evidence is thinner for that timing.

On a tired night, a 5-minute shower keeps the routine going, even though the research tested slightly longer sessions. Over a few weeks, you become someone whose evening winds down in the bathroom instead of on the phone. Most evenings, a warm shower, then a cool room, is all your body needs before the lights go off. If you lie awake most nights for weeks, or have a heart condition or low blood pressure that makes hot water a concern, talk to a doctor. Which moment in your evening already happens about 90 minutes before you go to bed?

References

• Haghayegh, S., et al. (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. doi.org/10.1016/j.smrv.2019.04.008
• Kräuchi, K., et al. (1999). Warm feet promote the rapid onset of sleep. Nature, 401(6748), 36-37. doi.org/10.1038/43366