We’ve written before about how the average toothbrush is believed to be harboring more than 10 million bacteria, including particularly nasty stuff like Staph and E. coli. This is partly due to the number of bacteria that live in your mouth—anywhere between 100 to 200 different species—but it’s also thanks to a much more unpleasant phenomenon we like to call Toilet Flush Blast Radius. Essentially, every time you flush, tiny particles of fecal matter are flung into the surrounding area, coating anything within six feet of it.
Considering this, it might sound smart to protect your toothbrush from germs by storing it in travel container or routinely using a toothbrush cover. But according to the American Dental Association (ADA) and the Council of Scientific Affairs, that only makes matters worse: “A moist environment such as a closed container is more conducive to the growth of microorganisms than the open air.”
A 2015 study performed by the American Society for Microbiology came to the same conclusion. “Using a toothbrush cover doesn’t protect a toothbrush from bacterial growth, but actually creates an environment where bacteria are better suited to grow by keeping the bristles moist and not allowing the head of the toothbrush to dry out between uses,” explains researcher Laura Aber.
So rather than covering your toothbrush to protect it from flying dookie, the ADA recommends rinsing the brush thoroughly after each use, then allowing it to air dry in an upright position. Closing the toilet lid before flushing will also minimize the spread of germs.
None of this means your toothbrush cover is obsolete, though: The ADA recommends consumers replace toothbrushes approximately every three to four months or sooner if the bristles become frayed, but you may be able to add a little more life to your bristles by using that handy toothbrush cover when traveling—just make sure the brush is completely dry before slipping on its little, plastic helmet.