It should be obvious. I found a 10 year old N95 mask in a drawer that I wore a few times ~10 years ago when the San Diego wild fires and Smoke were a thing. I wore it for the first time tonight going into a grocery store. Can't donate it to a hospital/first responder because its 10 years old and been worn. Don't know how degraded it actually is due to age/use but if I have it I'm wearing it.