Every time we pass them along our teeth, we trust that our toothbrushes are handling business and getting rid of disease-causing plaque, which is full of bacteria. But if you're using an old toothbrush you’re not doing your mouth any favors. You see, while many of us know how important it is to take care of our teeth, we aren’t as diligent when it comes to taking care of our toothbrushes.

Toothbrushing plays an essential role in personal oral hygiene. However, if you’re brushing your teeth as often as you’re supposed to — twice a day, in the morning and right before bed — then the bristles on your toothbrush are becoming frayed and worn with each use faster than you realize. This isn’t a good thing since worn-out brushes won’t efficiently clean teeth and become less effective at fighting off decay.

“As your bristles start to fray, they are not actually getting in between your teeth. You may not be as efficient at brushing your teeth,” Dr. Jonathan Abenaim, dentist and clinical instructor at New York University, told Medical Daily. “There may be bacteria or a few particles left behind if you don’t have the right toothbrush.”

A frayed toothbrush can be an inconvenience, but the solution is simple: replace it. The American Dental Association recommends that consumers replace toothbrushes approximately every three to four months, or possibly sooner if you’ve been sick. It’s also important to note that you’re not just throwing away your toothbrush, but millions of bacteria.

One study from the University of Manchester in England found that the average toothbrush contains at least 10 million bacteria — including E. coli and Staph. When you think about it, this makes sense since at any given time there are about 100 to 200 oral bacteria species living in your mouth, most of which end up on a toothbrush after a single brushing. In fact, a new toothbrush can become contaminated with bacteria, viruses, and fungi (living in the mouth or from the external environment) after just 30 seconds of use. What’s more, these germs don’t just stay on the toothbrush, they can also be transmitted to other toothbrushes in the household, increasing the risk of infection with each use.

In other words, swapping out your toothbrush every three to four months is just as important as brushing twice a day and flossing when it comes to maintaining your oral health.