Do you reuse your KN95s?
November 17, 2021 11:34 AM

I know technically we're not supposed to, but I have like three on rotation that I will use for short trips to the grocery store or to pick up a takeout order or something. For days where I need to be at the office the whole day, I will use a fresh one and then throw it out at the end of the day. But is it okay to actually reuse them sometimes?
posted by thelasttango to Health & Fitness (20 answers total) 9 users marked this as a favorite
I can say that I do reuse them in a similar way. My naive view is the protection from the mask for intermittent use is not going to deteriorate over a few days. I have no scientific evidence for or against this!
posted by crocomancer at 11:48 AM on November 17, 2021




You're supposed to be able to wear each for 8 hours, so if you're wearing them on short trips, that should last multiple days.
posted by MythMaker at 12:01 PM on November 17, 2021


I use my KN95 masks until they've had a cumulative life of 8ish hours, as long as nothing else happens to them. I do the same with the insertable filters for other masks--they're supposed to last 8 hours as well.
posted by assenav at 12:04 PM on November 17, 2021


You can reuse them for a period of time, but not indefinitely. You should not reuse them if:

- the straps lose tension and can't hold a seal against your face, which can happen with non-elastic straps (specifically a problem with N95s)
- appear visibly soiled
- have been soaked in liquid
- smells funny
- have been used for a period of time (see next paragraph)

All the masks/respirators that are certified are technically going to degrade when you breath outwards, because your exhalation has moisture which damages the mask material. There aren't a lot of studies on this, but I'll defer to someone who's actually tested (with scientific equipment) their used masks:

How long can you wear a KF94 or KN95? How to get a good face fit and more! (YouTube)
posted by meowzilla at 12:08 PM on November 17, 2021


I buried the lede - there wasn't significant degradation of the filter material after 40 hours of use. Honestly by that time, the mask starts looking visibly damaged due to taking it on/off anyway, and that's a reason to replace it.
posted by meowzilla at 12:15 PM on November 17, 2021


I do. There have been various studies showing that masks can be successfully decontaminated and reused (here's one that talks about reusing it three times, but I've seen more, and they're talking about healthcare). If you're just going in a grocery store for 20 minutes, you definitely don't need to throw it out immediately. I've been rotating- if you're not doing anything to decontaminate the mask, you can wait several days before wearing it again so any possible virus can disappear. Eventually, the moisture from breathing through the mask can saturate it, I think, but I don't know what that threshold is.
posted by pinochiette at 12:15 PM on November 17, 2021


I reuse them until they start having issues, as mentioned above. I read somewhere to give them five days in between reusing, which is what I do. I rotate through six masks until one of them has a problem.
posted by jenfullmoon at 12:19 PM on November 17, 2021


I reuse them until they get dirty or start to smell. At this point in the pandemic I don't feel we need to act like we're in The Hot Zone 24/7. KN95 masks are expensive, they consume resources, and they end up in landfills. No need to cycle through hundreds of them per person per year.
posted by Winnie the Proust at 12:36 PM on November 17, 2021


My partner wears KN95s to school and we read that you can bake them at a low temperature to reuse them. So he wears one to school and it goes in a "used" pile, and then every so often we bake them. I believe this is what we read but it was a while ago.
posted by Medieval Maven at 12:38 PM on November 17, 2021


My university's official policy is that non-healthcare staff who use N95s should have five masks per month, allowing each to rest for a week between uses and replacing any that are wet, dirty, badly fitting, etc. Healthcare staff get more masks and have more fit testing, etc. The university provides masks to employees and has in general been pretty good about enforcing mask use on campus, so I feel like they aren't just, like, making something up.

I am not sure that I would use an single N95 in short bursts over the course of six months or a year, since eventually they do lose their electrostatic charge, but I do keep one in my backpack for short trips into the post office, etc. So far, I tend to break the straps after a while, so I haven't had any "is this mask too old" concerns.
posted by Frowner at 12:41 PM on November 17, 2021


Also, for me, I'm not too worried about contaminated masks. If I worked in a school, or if I wore one to a clinic, I'd be more careful about decontamination time, etc, but there is no real evidence of fomite transmission in ordinary settings and in general I'm only going into places where almost everyone is masked and I can social distance most of the time. I figure the odds of there being enough covid in the air to make my mask itself infectious are pretty low in the off hours at the grocery store or in the post office where the employees feel very comfortable about bullying people into masking. (My post office is the best.)
posted by Frowner at 12:43 PM on November 17, 2021


Mask fit generally degrades before the material. That said, KN95 masks available to the public without formal fit testing are very frequently poorly fitting even from the start.
posted by Easy problem of consciousness at 12:58 PM on November 17, 2021


For the first year of the pandemic, Dr. Advicepig reused the same 5 masks in rotation at the hospital. She still can hardly stand to part with one. As long as it still fits well, it's fine.
posted by advicepig at 1:35 PM on November 17, 2021


All the time.
posted by stray at 2:25 PM on November 17, 2021


I forget the exact number I heard for healthcare workers but it was on the order of 5 or 8 don/doff (put on / take off) cycles. I use mine a bit more than that, but that's a good number to have at the back of your head I think. I use a binder clip at the back of my head to hold tension on mine so they're never not tighter than they would be out of the box without it.
posted by wotsac at 6:39 PM on November 17, 2021


I let my kids wear theirs for two school days or until they're visibly dirty, whichever comes first.
posted by potrzebie at 7:02 PM on November 17, 2021


I don't. If I do I get maskne.
posted by Jane the Brown at 9:35 AM on November 18, 2021


I forget the exact number I heard for healthcare workers but it was on the order of 5 or 8 don/doff (put on / take off) cycles

I've been going into the office a couple days a week, and since I'm currently working in a single-occupancy office space with a door, I keep the door closed and my mask off except when I need to go to the printer/restroom/kitchenette. I probably don and doff my mask more than 8 times in a single day, but since it's only for 5 minutes at a time, I don't think it's worth counting that towards accumulated time/wearing.

At this point, I change to a new mask when it feels like the fabric has gotten perceptibly softer and isn't standing away from my nose as well, or if the fit around the cheeks and chin feels like it's getting worse. It's been working out to about once a week, since I'm generally able to stay home and/or distance (and I live in an area with a high vaccination rate).
posted by Lexica at 10:47 AM on November 18, 2021


> I probably don and doff my mask more than 8 times in a single day, but since it's only for 5 minutes at a time, I don't think it's worth counting that towards accumulated time/wearing.

Is the don/doff count because of stretching the elastic? I know my N95 feels different after lunch, and that's just two dons and one doff.
posted by The corpse in the library at 6:29 PM on November 20, 2021


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