In urban settings, our skin is constantly exposed to harmful UV rays and air pollutants. UV rays such as UVA and UVB can penetrate through clouds, rain, fog, and even windows, which can cause premature aging or dark spots. Meanwhile, air pollutants such as PM 2.5, which is thirty times smaller than human hair, can easily penetrate the skin and cause skin damage, wrinkles, premature aging, dull skin, acne or inflammation.