You should probably replace some of your fabric face masks

If your masks are beginning to feel as old as this pandemic, it’s probably time to get yourself some new ones.

Even if you’re vaccinated, it’s still a good idea to wear a mask indoors whenever possible. In July, the Philadelphia Department of Public Health issued new guidelines where it “strongly recommends” that you wear a mask indoors, even if you’re vaccinated (and wear two masks if you’re not), gather outdoors when you can, and avoid crowded indoor spaces.

This is, of course, because of rising cases and the danger of the delta variant. If you’re vaccinated, you are much less likely to get very ill, but you can still become infected and infect others.

So don’t throw out your masks yet.

» READ MORE: Here’s what you should know about vaccines and COVID-19 variants.

The Centers for Disease Control and Prevention advises using masks that have at least two layers of tightly woven, washable, breathable fabric, such as cotton. When you wash your masks regularly, which you’re supposed to do, the fabric, as well as the fit, can begin to deteriorate. As this happens, your masks become less effective.

“A newer, fresher mask is likely to have tighter fibers, and so it’s likely better at keeping out other particles and keeping your particles in,” says Krys Johnson, an epidemiologist and assistant professor at Temple University.

» READ MORE: How to do clean your fabric face mask properly

The exact timeline of when you need to replace a mask depends on the makeup of the mask, along with other factors like how much you’re washing it and how often you’re taking it on and off.

But as a general rule of thumb: “Think about masks like seasonal attire. Update every season,” says Johnson.

Here’s how else to know if you should replace a mask.

A snug fit is key. If the elastic of your ear loops starts to loosen, it’s time to reach for something tighter.

That’s a bad sign, says Johnson, and may indicate that the fabric is deteriorating or was too thin from the start.

A mask needs to cover your nose and mouth in order to work. If one of the straps falls off and you have to keep touching your mask to keep it in place, this defeats its purpose.

This is perhaps the most obvious sign of all. If your mask is ripped, it needs to go. It doesn’t matter how small or large the hole is.

Experts strongly recommend owning more than one mask. And in the winter, you’ll want to carry a backup. Moving from chilly outdoor environments into cozy indoor settings makes it easy to sweat through your mask, as does wearing multiple layers. You’re advised to always swap a wet mask for a dry one. A wet mask can make it harder to breathe. And of course, it’s uncomfortable, especially if you’re walking back outside into cold temps.

When in doubt, replace it, says Johnson. We want to eliminate risk as much as possible right now, and proper mask wearing is part of that.

If you have a disposable mask, the CDC advises throwing it away after you’ve worn it once.

This article has been updated since it first published.