If your toothbrush’s bristles can no longer stand up straight, that’s a surefire sign it’s time to buy a new brush. Bent, frayed, or excessively worn bristles simply aren’t going to be as effective at removing plaque and other particles from your teeth compared to bristles that are in better shape. So every 3 to 4 months change your toothbrush.

While it’s important to keep up your tooth brushing routine while you’re sick, this also means your toothbrush will be exposed to all the extra germs floating around in your mouth. To avoid reintroducing those germs into your mouth after you’ve recovered, it’s a good idea to purchase a new toothbrush whenever your illness breaks.

Bacteria and leftover food can combine together to form plaque on teeth, which is a sticky, bacteria-containing biofilm. This plaque then feeds off sugar and starch from the food you eat to produce acids which, in turn, can erode the outer enamel layer of your teeth and lead to cavities and even tooth loss.

Most experts, recommend buying soft toothbrushes.“Hard toothbrushes have hard, stiff bristles that don’t flex and don’t bend and don’t sweep down under your gum,” says Dr. Cram. “Soft bristles do a much better job of getting into more nooks and crannies.”

Also, look for brushes that have lots of bristles as opposed to sparse ones. “It’s better to have lots of bristles, then as you’re making a circular motion with the brush, you’re actually getting the little bristles to sweet under the gum tissue,” advises Dr. Cram.

In between uses, stand the brush upright—away from other toothbrushes—in the open air. Covering them up or putting them in a container can actually encourage bacteria growth.