I'm certain the people unnecessarily infected with Covid-19 will be glad, as they pass away, that the cough that killed them wasn't suppressed by an out-of-date mask.

"Expired" might mean that the mask material has disintegrated and could itself be sucked into the lungs. Or perhaps it means that fungal infections could have grown in the masks. Or maybe the government really made a decision based on short term thinking and tossed the masks to make room for piles of salt or something. Or maybe the cost of storing masks really isn't worth it because there's lots of things that can decimate society (nuclear war?) and we needed to more urgently spend money there. Who knows, right?

"Expired" mostly seems to mean that no-one has tested that they still meet specs beyond that date, because there's no commercial incentive to do so. Similar thing with expiry dates on many medicines.

Along those lines, Meltblown fabric used in N95 respirators is made from plastic by some incredibly high tech machines. Each costing $5m per machine (line): https://www.reicofil.com/en/pages/meltblown_lines

You’re absolutely right. When a mask is expired, it should not be used. There is a reason for the expiration date and it’s not just for profiteering or some malicious motive.

Lot of expiration dates you see in medicines is FDA regulated and should be taken seriously.

Some expiration dates are important. Many, perhaps most, are arbitrary, fake, or ultra-conservative – optimized to minimize liability & maximize repurchases in non-emergency situations.

An expired mask will almost certainly be better than no mask. And especially so stored well with no visible degradation – it's heat & contamination by elements that could jeopardize their essential properties.

(Some N95 masks I bought during last year's northern California fires are individually sealed in cellophane with no expiration date. Stored in a cool, dry place they'd likely be fine decades from now. If some governments bought flakier masks in more-fragile packaging with early expiration dates, that's on them.)

As a consumer, how do you know which ones are to trust and which ones to not?

How do you know that your N95 mask is “fine”? Ultra fine submicron particles in your lungs can lead to a lot of problems. These fibers are essentially plastic.

How does one know anything's "fine"? Your senses & accumulated evidence.

Let's say it's the Zombie Uprising of 2040, and I open a well-stored, individually-wrapped N95 mask from 20 years ago.

It's got no expiration date on it (as per the ones I bought last year), & it looks good, & doesn't give off any dust, & it smells the same as I recall new masks smelling. I'll figure that's "fine" – unless & until someone has specifically shared some study demonstrating their dangerous-yet-imperceptible degradation.

Is there such a study, or is this just "there be dragons" fear-of-the-unknown?

> Lot of expiration dates you see in medicines is FDA regulated and should be taken seriously.

This is not true. The FDA dates are ultra-conservative for liability reasons. The military has done a lot of research (well, asked other people to do research) on this, and found that the vast majority of "expired" medicine is perfectly fine:

> To save money on regularly replacing its drug stockpile, in 1985 the US Air Force asked the FDA to test some products. Since then, the FDA has found that 90% of over 100 prescription and over-the-counter drugs tested could be used safely past their expiration date, a Pentagon spokesman told the Associated Press, adding that the dates tended to be very conservative. Products were tested by either the manufacturer or the FDA, but always with agency supervision.

Source: https://www.thepharmaletter.com/article/fda-tests-let-milita...

The CDC has literally outlined which expired masks are acceptable and which are not:

https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/FAQ-N95.aspx

Take that for what you will.

I speak from experience. Most expiration dates for this kind of thing are absolutely meaningless. I see expiration dates for sealed glass containers of water, methanol, dry chemicals stored at -80C, etc. It is all complete bull.

That's probably because there's a legal obligation to put an expiration date on it. Where I live all consumables have to have an expiration date so there is a best before date on table salt. Salt. Most likely this is because it's cheaper and easier to put an expiration date on everything rather than discussing the exceptions on a case by case basis.

The only food I can think off that literally says "last forever if stored properly" is sugar.

Eg. soda stream bottles (the water container) have an bogus expiration date, honey have expiration dates ...

When decades-old drugs were tested, nearly all were found to be just as effective as when they were new.

All an expiration date really means is they never bothered to test the efficacy beyond a couple years, but the compounds are remarkably stable.

https://www.npr.org/sections/health-shots/2017/07/18/5372578...

Expired masks are better than no masks. I hope they didn't get tossed.

At the very least, give them to service workers.