Remember how in college, you had your prerequisite major courses — like accounting 101 or microbiology — and then you had your okay-to-sleep-through electives? Well, for a long time, face masks were kind of like the latter. They were the "Introduction to French Wines" in your everyday skin-care schedule, in that they were fun and served you some purpose, but they weren't exactly necessary. Then everything changed when the K-beauty wave hit the states. Suddenly, there was a treasure trove of mask innovations that made them more useful than ever.