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My college roommate was the first person I met who regularly used a face mask. At 21, I was already well acquainted with plenty of extensive beauty routines; my grandma even insisted on taking her moisturizer with her into hospice care. But the American beauty market still mostly ignored face masks in the mid-2000s. They seemed to me like things that were administered in spas, alongside mud baths and cucumber-slice eye patches—luxurious, but also a little silly.

I often considered squeezing out a little bit of my roommate’s Queen Helene Mint Julep to try it myself, but my mother always said to respect another woman’s product. I soon had my chance anyway. During the decade since I left college, the popularity of masks has acted like a beauty-industry aerosol, expanding to fit every skin problem, every trendy ingredient, and every cutting-edge delivery method, filling medicine cabinets across the country in the process.

The definition of the word has expanded, too. A night cream is a mask. Serum-soaked eye patches are a mask. A product you leave on your face for only 30 seconds is a mask. In addition to their face, people can now mask their lips, neck, chest, breasts, and butt. America is at Peak Mask, and the reason we got here is more than skin deep.

The maskification of American skin care has happened during an unprecedented boom for the face-goop industry as a whole, both in the United States and beyond. In 2018, Americans spent more than $5 billion on high-end skin care, according to one estimate—13 percent more than the year before. The global skin-care market is projected to expand by more than 4 percent through 2025, and face-mask sales are expected to grow at almost two and a half times that rate.

In the United States, that growth wouldn’t be possible without the influence of Korean skin-care companies. For a long time, “good” skin-care products in America were expensive and old-fashioned, and more accessible options weren’t very good. Meanwhile, as the journalist Alex Abad-Santos has written, those made by Korean brands generally boasted more advanced ingredients. Early adopters in the U.S. sought out Korean products through online recommendations and skin-care forums, and demand grew as more people were captivated by the (sometimes exoticizing and orientalist) lore of the country’s skin care. By the mid-2010s, both prestige beauty retailers such as Sephora and big-box stores such as Target were picking up Korean products.

Through that proliferation, Americans were introduced to the product that has influenced the mask boom more than any other: sheet masks, the tissue-thin, face-shaped fabric sheets drenched in liquids, intended to moisturize, plump, brighten, or otherwise improve the look of your skin. “Sheet masks are a great gateway to beauty products” because they cost only a few dollars each, says Charlotte Cho, a co-founder of Soko Glam, a U.S.-based retailer of Korean beauty products. And they’re frequently sold in single-use packets, which makes the stakes of buying one feel pretty low.

Even with novelty and accessibility on their side, sheet masks’ meteoric popularity probably wouldn’t have been possible without Instagram Stories. The tool, launched in late 2016, lets users create daily strings of photos that disappear after 24 hours. That expiration date freed people from the pressure of creating a perfectly composed piece of digital art that will live on their account forever, and it loosened the platform up considerably for its mostly young, mostly female user base.

In 2017, photos of regular people and celebrities alike sporting creepy, damp-looking sheets stuck to their heads had become one of the dominant tropes of the Stories format. The journalist Anna Silman wrote in The Cut at the time that there’s “something weirdly performative about our current sheet-mask epidemic, in which posting a photo of yourself looking like a Goop-ified Freddy Krueger somehow comes to signify ‘I look after myself’—an elaborate put-on, in which the appearance of self-care becomes more valuable than the act of self-care itself.”

Although people tend to apply masks at home, they’re far easier to broadcast on social media than serums or exfoliants. Masks usually have a color, they sit on your face for an extended period of time, and they connote a period of inward-focused leisure that feels a bit aspirational—and perfect for Instagram. If skin care has become a Millennial “coping mechanism,” as the journalist Jia Tolentino called it in The New Yorker, then showing everyone your mask assures them that you’re coping just fine. (Whether that’s true is a different story.)

It didn’t take long for American brands to note both the hunger for masks and the apparent desire of young, stylish women to talk about them publicly. Now there are new types of masks coming at shoppers from every angle: gold masks, bespoke 3-D-printed masks, rubber masks, sheet masks that make you look like a cartoon animal for selfie purposes, and masks you’re supposed to sleep in. Sephora now offers more than 300 mask varieties on its website, and they include such ingredients as charcoal, cannabis extracts, probiotics, and algae.

But that’s the problem with booms: Intense consumer interest leads to an avalanche of products, which eventually renders all of them less novel and exciting than the viral hits that came before. Even if that fatigue isn’t yet widespread enough to affect global face-mask growth projections, it’s already hitting some consumers, who are looking to streamline after going all in on lengthy skin routines.

I’d be the first to admit that I’ve embraced Peak Mask with my whole wallet. My bathroom currently contains 11 sheet masks, six conventional masks, two hair masks, a tub of eye masks, and a peel that is arguably also a mask. My current favorite is the super-popular Summer Fridays Jet Lag Mask, which is a heavy cream you put on at night and don’t wash off before going to bed. It’s great, but I don’t know how it’s different from the night creams of my grandmother’s era.

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