How Brushing Your Teeth Hurts
Brushing your teeth, particularly with an electric toothbrush, can actually push germs under your gums, says R. Thomas Glass, DDS, PhD, professor of dentistry and pathology at Oklahoma State University Center for Health Sciences.
Most of these germs already exist in your mouth so you probably won't get sick from them. However, if others use your toothbrush (or you use someone else's) germs can be spread.
The thing to worry about is recurring illness. "When your resistance is low, that's when this becomes clinically important," he says. "In essence, you are re-infecting yourself," says Glass.