Most of us know our toothbrushes aren’t meant to last forever. But it can be hard to figure out when our beloved bristles are nearing the end of their natural lifespan.

You might be surprised to find out that according to manufacturer guidelines and dentist recommendations, your toothbrush should be replaced every 12 to 16 weeks.

There are also cases when you might need to replace your toothbrush sooner. If you don’t replace a toothbrush or electronic toothbrush head when it needs to be, it can affect your dental health and spread infection.

Your toothbrush is your first line of defense against the bacteria that cause gum disease, tooth decay, and bad breath.

Straight bristles and a clean and easy-to-grip handle are best to navigate the smaller spaces in your mouth. A soft bristle brush will effectively remove old food and bacteria that can collect around the bases of your teeth.

If you follow the standard recommendation of brushing your teeth for 2 minutes twice per day, you’re already taking steps to protect your teeth from cavities.

Brushing your teeth between each meal and after a sugary snack is an extra step you can take to be proactive about preventing tooth decay.

Brushing two or more times per day is still considered standard for a manual toothbrush. At this rate of use, the bristles in your brush will start to fall out and become mangled or twisted within about 3 months.

The Centers for Disease Prevention and Control (CDC) also advise to replace your toothbrush every 3 to 4 months, or whenever it appears to be getting worn out.

Once the bristles in your toothbrush start to lose their stiffness, the toothbrush is almost ready for the trash. Without bristles that brush aside food and plaque, your toothbrush quickly loses its efficiency.

Electric toothbrush heads clean the surface area of your teeth by quickly rotating or vibrating. These toothbrush heads still have nylon bristles that can wear after regular use. What’s more, those bristles are shorter, which means that they may fray more quickly.

Plan to change out the toothbrush head on your electronic toothbrush every 12 weeks, or even earlier. Watch for signs of wear and tear on the bristles to know when it’s time to say goodbye to a brush head.

If you or a family member have been sick, it’s a good idea to replace your toothbrush as well as the toothbrush of everyone else in your household.

Viral and bacterial infections such as strep throat are of particular concern and are a good reason to switch your old toothbrush for a new one.

You might want to change out toothbrushes for children more often than every 3 months, as they may mash on a toothbrush head or gnaw on the handle.

Don’t forget to watch your child when they’re brushing their teeth to make sure they aren’t exposing their brush head to any other surface besides their teeth.

If anyone else uses your toothbrush by mistake, get rid of it. It’s better to be safe than sorry, and everyone’s mouth harbors different bacteria than yours.

To make the most out of your toothbrush, take care of it the way you would any personal grooming or hygiene tool.

Don’t share your toothbrush with someone else, even members of your immediate family. If your toothbrush is stored in a cup or container with other toothbrushes, try not to let the heads touch each other.

After brushing, rinse your toothbrush completely with tap water. You don’t need to use a disinfectant, mouthwash, or hot water to sanitize it. Trying to “sanitize” a toothbrush in this way can actually spread germs.

You also don’t need a special closed container to keep your toothbrush clean when it’s not in use. Some of these containers can encourage mold growth or spread bacteria.

Every time you use your toothbrush, the nylon bristles are exposed to water and chemicals from your toothpaste. This makes the bristles a little weaker with each use. The bristles bend and twist into a new shape, which is known as “bristle flaring.”

A 2013 study showed that after 40 days of consistent use, bristle flaring starts to make your toothbrush less effective. Study participants who didn’t replace their toothbrushes on the 40th day of use experienced considerably more plaque buildup.

At least two earlier studies on worn toothbrush heads confirmed that older toothbrushes are much less efficient at removing plaque, which is the cause of gum disease and tooth decay.

Your toothbrush is an important oral hygiene tool. To maintain your toothbrush and make the most of its lifespan, use only your own toothbrush and store it upright and let it air dry.

Plan to replace the toothbrushes of every person in your family every 3 to 4 months, and mark your calendar on the date of the purchase so you remember when it’s time to replace them again.