How often should you change your toothbrush and why? When to Get a New Toothbrush Replace toothbrushes every 3 to 4 months. Consider getting a new toothbrush sooner if you have been sick, especially if the toothbrush is stored close to other toothbrushes. When in doubt, look at the bristles. If they are frayed, they won't clean teeth as thoroughly. Why should you change toothbrush? The bristles break down and loose their effectiveness in getting to all those tricky corners around your teeth. It is also important to change toothbrushes after you've had a cold, the flu, a mouth infection or a sore throat. That's because germs can hide in toothbrush bristles and lead to reinfection.