Most dentists agree you should change your toothbrush every three months.Studies show that after three months of normal wear and tear, toothbrushes are much less effective at removing plaque from teeth and gums compared to new ones. The bristles break down and lose 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. Even if you haven't been sick, fungus and bacteria can still develop in the bristles of your toothbrush—another reason to change your toothbrush regularly!