Germs thrive in moist environments such as your toothbrush, notes Gerba. Add that to the fact that research in the 1970s discovered toilets spew fecal bacteria into the air every time they are flushed, so chances are, your toothbrush is teeming with microbes. To protect your mouth, replace your toothbrush every three to four months and close the toilet lid when flushing.
