It’s almost guaranteed that at some point, while scrolling through your social media feeds, you’ve seen photos of your friends—or celebrities—smiling while doing their best impression of Jason from Friday the 13th.

Okay, not exactly. But proudly looking like a horror movie villain is just one of ways that Korean sheet masks—the buzzy beauty routine that has taken selfie-loving Americans by storm—have left their (not always visible) mark.

Why is just about everyone obsessed with them? “Sheet masks have been around for over a decade in Korea,” says Charlotte Cho, co-founder of Korean beauty site Soko Glam and author of The Little Book of Skin Care: Korean Beauty Secrets for Healthy, Glowing Skin. Their popularity can be explained not just because they’re highly photogenic, but also because, as she notes, “people are seeing results and they’re relatively affordable.”

“The sheet mask forms a sort of barrier that really locks the ingredients in and prevents that evaporation”

Indeed, a sheet mask serves a purpose beyond garnering “likes” on social media. According to the beauty guru, a lot of skin-care products actually evaporate when you put them on your face (yes, even the pricey ones). “It takes time for those ingredients to mingle with your skin,” she says. “The sheet mask forms a sort of barrier that really locks the ingredients in and prevents that evaporation,” which explains why your face might feel plumper and looks brighter after using one.

There’s also the fact that, as Cho points out, the sheet versions don’t get dry and hard like some other masks out there (think mud-based products that go on thick). “Clay really draws out excess oil, but sheet masks are providing moisture and hydrating the skin. And oily skin often needs moisture, even though many people don’t realize it,” she adds.

It makes for a very user-friendly experience—yes, sometimes to the extreme. “People get addicted,” admits Cho. “Some people in Korea use one daily—there’s a hashtag called ‘one mask a day.'” The typical $2 price per sheet helps fuel the habit, too.

Which isn’t to say that sheet masks are perfect: Turns out many of them are full of alcohol, PEGs, fragrance, and preservatives like phenoxyethanol and ethylhexylglycerin. So despite the trend factor, sheet masks may not be the cleanest beauty category. The good news? We did the legwork and found three that are as natural as they get.

So if you’re ready to look like a scary movie bad guy in the name of plump skin (and Instagram likes), read on for expert tips for getting the most out of your sheet mask ritual—plus the best toxin-free options out there.

Charlotte Cho’s list of sheet mask best practices:

• Use morning, night, or whenever. “They’re great for all times of the day because they don’t take much time, they’re disposable, and you don’t have to wash your face after,” says Cho.
• Start with a fresh face. “It’s best to start with a clean base, so washing your face and then toning is always a great practice,” she explains. “It helps prep your skin to absorb the amazing ingredients that will follow in the next step.”
• Set a 20 minute time limit. With other face masks, you might try to keep them on for as long as possible (maybe even wearing one through an Orange is the New Black marathon) so you can really see the effects. That’s not necessary with sheet masks. “Don’t sleep in it,” advises Cho. “If you keep the sheet mask on your face after it becomes dry, it starts to have the opposite effect and will draw moisture away from your skin.” Talk about scary….
• Skip the post-mask products. “Some sheet masks are very thick, while others are watery and absorb quickly into your skin,” says Cho. “If it’s watery and your skin gets dry throughout the night, then I recommend putting on a moisturizer on [your skin] afterwards. But if the mask is very thick, it’ll feel like a lotion on your skin after you remove it—and you can just rub [the mask liquid] in without supplementing with another moisturizer.”

Ready for a little self-care with sheet masks? These are the best all-natural options to buy.

Best anti-aging sheet mask:

Joanna Vargas Eden Mask, $75 (for pack of 5)

Best hydrating sheet mask:

100% Pure Ginseng Collagen Boost, $9

Best acne-fighting sheet mask:

Yes To Tomatoes Acne-Fighting Paper Mask, $3

Now that your skin is taken care of, what to do with your hair? Here are 11 seriously cool ways to rock the high ponytail—which all look cute with these wellness-obsessed statement tanks.