It happens to a lot of us; you go to grab your kitchen sponge to wipe down your countertops after dinner, and it stinks. It's not your fault — the kitchen sponge is one of the dirtiest things in the home. These factors are what make the common kitchen sponge the perfect environment for bacterial growth. The average kitchen sponge is made from polyurethane or, if you're more eco-conscious, cellulose. Using a sponge on multiple surfaces creates even more opportunity for bacteria to spread and accumulate in your sponge.