Long-wavelength ultraviolet rays (320~400 nm) have lower lethality than UVB, but the amount reaching the earth is higher than UVB (of which UVA accounts for 98%). No matter indoors, cloudy or rainy days, UV-A can make the skin tan and produce dark spots, which can penetrate deep into the dermis, destroy collagen fibers and elastic fibers, and make the skin lose its elasticity. Cosmetics industry further divides UV-A into UV-A1 (360-400 nm) and UV-A2 (320-360 nm), because studies have found that UV-A1 is the culprit in skin aging and even skin cancer.