If left uncleaned, a makeup sponge — like a Beautyblender — can get very gross, very quickly. Makeup artist Ashleigh Ciucci previously told Allure that "sponges are porous, so they hold onto oils, debris, and bacteria." And well, I think it's safe to say you probably don't want any of those things hanging around and penetrating a tool that you use on your skin every time you do your makeup.