Your body temperature is linked to your circadian rhythm: It drops about one degree in the hour before you go to sleep and reaches its lowest temp overnight. Taking a hot shower kickstarts this cooling process, which sends signals that it’s time to sleep, says study author Shahab Haghayegh, a Ph.D. candidate in the biomedical engineering department at the University of Texas at Austin.
If that seems counterintuitive, imagine blowing a hair dryer on your thermostat. “The AC system will think it’s hot and in turn, start to cool down the house,” Haghayegh explains. In the same way, your core temp rises while you’re under hot water, so your body works to reverse that increase.
The bottom line:
Take a hot shower in the two hours before bedtime for high-quality sleep. Haghayegh’s study found 104 to 109 degrees was the ideal water temp range, but he notes that as long as you feel comfortably hot, you should get the benefits. Taking a cool shower in the morning, on the other hand, will make you feel more awake, he adds.