Lucy Wallace, a 28-year-old consultant from Brooklyn, New York, refuses to go to sleep without showering first. It doesn’t matter if she already showered in the morning after working out — Wallace is obsessive about her bedtime routine. “I hate the idea of climbing into bed covered in the dirt and grime of the day,” she said. She even forces her boyfriend to do the same. “He hates me for it,” she admits. “But the thought of lying there, festering in your filth from the day — especially if I’ve been out and about in the city — I can’t do it.” Some people swear by their morning showers just like their daily lattes, while others, like Wallace, swear by the nighttime rinse. But what does science say? Does it matter when we shower? And how does it affect our skin, our body’s natural oils, and even our sleep? Here’s what three experts had to say.

The benefits of a morning shower are kind of obvious: It wakes you up and helps you get your head in the game. “A morning shower allows for time to meditate and regroup before starting a long or hectic day,” said Mona Gohara, MD, associate clinical professor of dermatology at the Yale School of Medicine. “This mindfulness can decrease inflammation in the skin by keeping levels of a hormone called cortisol capped.” That alertness will pay off if you have to shave, which Gohara said is best to do in the morning. Not only will you be more aware and less likely to cut yourself, “mornings are the best time to shave because that’s when you have a surge of platelets — or blood cloggers,” she said.

A morning shower may also be the best way to prime your face for the day ahead. “Our skin is at its best after your skin routine is done first thing in the morning,” said Yen Reis, founder of Skin Laundry. “This is prior to facing any free radicals, sun, dirt, or debris, which inevitably attack our skin the minute we walk out the door.” Plus a morning shower can stimulate the skin cells, specifically after they’ve relaxed during sleep, said Reis, who also said morning showers are best for combination, oily, or acne-prone skin. Avoid the temptation to make the water as hot as you can handle, though: “Lukewarm water is best,” Reis said. “While a morning shower can make your skin appear healthier, a too-hot shower can have the opposite effect, specifically for dry and sensitive skin.”

Evening showers, though, are the winners. For one thing, they also have skin-related benefits. Nighttime showers are a great way to remove all of the makeup, oil, dirt, and pollutants that have accumulated on your skin throughout the course of your daily activities, said Reis. Gohara adds, “Your skin naturally exfoliates and replenishes itself at night, so you leave a clean slate when the proverbial factory is open.” (The body’s oil production peaks at 1:00 p.m.)

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But the strongest argument for showering at night may be the exact reason Wallace does it. “When you get into bed, you should feel clean,” said Nancy Rothstein, who calls herself The Sleep Ambassador. “You’ve been out and about all day — why would you want to get into bed like that?” Also, Rothstein points out, “A nighttime shower is an integral part of your ‘preparing for bed’ routine. It’s time for you — no phone, no emails, just the luxury of fresh, warm water flowing over your body. Call it an opportunity to shower yourself with mindfulness!”

The temperature of your evening shower matters too. Rothstein said “warm but not too hot,” is best for getting the body relaxed and primed for sleep without putting you at risk for overheating during the night. “Think of your shower as a segue to sleep,” Rothstein said. “The better you sleep, the better your hair and skin will look. So even if you’re exhausted and just want to crash, get in the shower and let the water run on your face and body.”

So there are reasons to shower in the A.M., and even better ones to shower at night. Should you just do it twice a day? Dr. Gohara warns this may just over-dry your skin and exacerbate any preexisting skin conditions. If you’re set on two-a-days, though, she recommends sticking to a mild water temperature (“extremes disrupt the skin barrier,” she explains) and using the best cleanser for your specific skin type.

Ultimately, Gohara said, the cleanser you use in the shower may be more important than the time of day you use it. “The wrong cleanser can wreck your skin,” she said. “If you use a standard soap — a cleanser that has a basic pH — it strips the skin of natural oils and compromises the skin barrier, leading to irritation and dry, lackluster skin. Using a mild, pH-neutral nonsoap cleanser helps moisturize while you cleanse and deposits skin-identical lipids back into the skin.” (Dr. Gohara’s favorite is the Dove Beauty Bar.) And when you’re done cleansing, lather on a proper moisturizer and some SPF.

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Since the skin’s natural oils fluctuate and increase throughout the day due to environment and hormone fluctuations, showering — whenever you choose to do it — can help control some of the oil we produce and help to remove some of the surface bacteria that can contribute to breakouts, Reis said. “Especially in hot, humid settings, oil production can kick into overdrive, so showering and cleansing the skin appropriately is a great way to control some of the excess oils.”

The bottom line? “If you like to shower in the morning, do it,” said Rothstein. “But definitely shower at night. It’s so important to go to bed clean, and it separates the day from the night.” (Rothstein is also a fan of shower caps so you can shower at night without having to sleep on wet hair or deal with the blow-dryer.) And for the love of your sheets and the sanctity of your sleep, if you refuse to shower before bedtime after a day bopping around in sandals, at least give your feet a solid scrub. No one wants to go to bed with — or next to — dirty flip-flop feet.