covid19

However, because the vast majority of COVID-19 cases do not require hospitalization, many more cases of long COVID have arisen from these milder cases despite their lower risk.

Basically until it's visible soiled.

When wet doesn't work as well, but fine again when dries

N95: american

Approved by the U.S. National Institute for Occupational Safety & Health (NIOSH). So, if an N95 mask is given the stamp of approval from NIOSH, it offers that certified level of protection.

Kn95: chinese

However, KN95s (and the similar KF94 masks) are mostly made—and vetted—in China or South Korea. If they are stamped as “NIOSH-approved,” they are actually fakes.

typos on packages

Mask will be stamped with “GB 2626-2006” or “GB 2626-2019"

The packaging must indicate the manufacturing date. Two- to three-year expiration date

Both:

If a mask or box has the FDA logo, then fake. "The FDA logo is for the official use of the U.S. Food and Drug Administration (FDA) and not for use on private sector materials," the FDA website says.

Should be in a 'marked packaging' (brand name?)

Should include manufacturer's name and address

kf94: korean