You never know just who's using your toothbrush if you leave it out. And that toothbrush that you have sitting next to the toilet? When a toilet is flushed, particles fly 6 to 8 feet — possibly reaching that nearby toothbrush. The ADA recommends switching toothbrushes every two to three months with brushes with translucent bristles. They harbor less microbes. Put it in a drawer or the medicine cabinet between brushes.