We all know that reusing the basic surgical mask is not recommended, but how about the other types of masks, like FFP2 or N95?

It depends, but you should be able to use FFP2s, N95s and KN95s a few times.

The United States Centers of Disease Control and Prevention says health care workers can wear an N95 mask up to five times. But experts say how often the average person can safely wear one will vary depending on how it’s used.

Using the same mask to run to the grocery store, for example, is very different than wearing it all day at work.

The amount of time a mask is worn is more important than how frequently it’s worn, says Richard Flagan, who studies masks and aerosols at the California Institute of Technology.

In general, he recommends limiting the use of an N95 mask to about two or three days.

With every breath you take in an N95, particles accumulate on the mask, Flagan says. That could make it more difficult to breathe if the mask has trapped a lot of particles.

"They are degrading the performance of the mask," Flagan says.

The elastic band on the mask could also get worn out and not fit around your face as snugly. It might also get dirty or wet, especially if you’re using it while exercising.

If you notice any of these changes to your mask, it’s time to stop using it – even if you’ve only used it a few hours. And since N95 masks can’t be washed, they should be thrown away once you can no longer use them.

FFP is the European standard for particulate respirators, similar to the U.S. standard of N95, which filters out 95% of aerosols.