On the one hand, a PM shower washes away the day. On the other, a morning rinse wakes you up. But preferences aside, where does science come down on this issue?
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Is there a right time to shower? Some people prefer to shower at night, washing away the grime and sweat of the day, so that they can hop between the sheets nice and clean. Others can't imagine starting the day without a thorough rinse-it's a wake-up call that rivals a steaming mug of strong coffee. But personal choices aside, is there any real benefit to showering at night or in the morning?

Turns out, nighttime washing has the edge when it comes to sleep benefits. "Showering or taking a bath prior to bedtime can help improve sleep quality and help you to fall asleep faster," says Elizabeth Culnan, Ph.D., a postdoctoral fellow in behavioral sleep medicine at Rush University Medical Center. "The key is in the timing: Showering 1.5-2 hours before bed will warm your body and then also allow you to experience a more pronounced dip in body temperature, which promotes sleep." (Related: 5 Ways to Reduce Stress After a Long Day and Promote Better Sleep at Night)

In fact, a nighttime shower or bath could be especially beneficial in warmer climates (or during the summer months), says Mia Finkelston, M.D., a board-certified family physician who treats patients via telehealth app LiveHealth Online. "In hotter weather, it may be difficult to get the natural drop in body temperature needed for good sleep-that's where the shower or bath can help," she says. "This drop in body temperature causes our body to slow down our heart rate, breathing rate, and digestion-getting our bodies into the perfect rhythm for optimal sleep."

Don't wait too long before bedtime to get clean, however, or you might end up awake all night. "If you shower too close to bedtime, it can heat the body and not leave enough time for your body temperature to dip," warns Culnan. "This might leave you feeling more alert, and less able to fall asleep when you want to." (Related: Why a Bath Can Be Healthier Than a Shower)

As for a morning shower: There are no real scientific advantages to it, though experts acknowledge it can still be beneficial to some. "Taking a shower as part of a daily, morning routine may also serve as what we call a zeitgeber-basically an external cue that provides information to the brain's clock that it's time to start the day," says Culnan.

But here, too, the details matter. "A shower can invigorate your senses, as long as it's not too long or too hot," explains Jaquel Patterson, ND, MBA, president of the American Association of Naturopathic Physicians. "If the temperature is too warm, it can have a relaxing effect." That said, if you really love a hot shower in the AM, Patterson suggests following it up with a cold blast. "Naturopathic doctors often recommend a thousands-year-old practice called hydrotherapy, which includes alternating hot and cold temperatures to awaken your system, increase blood flow, and support your immune system," she says. (Related: 10 Reasons Showering at The Gym Is The Best Thing Ever)

Ultimately, if your primary goal is to be clean, there really is no wrong time to shower or bathe. Any other sleep or wake benefits are just an extra perk of this daily ritual.

This story originally appeared on RealSimple.com by Melanie Mannarino.