Do N95 Masks Help? Yes!

by Chris

Do N95 masks really help? Someone on twitter pointed out that N95 filters down to .3 microns. SARS, which is a coronavirus, is 100nm according to NIH (link below). 100nm is .1 microns, so would the 2019 nCov be similar in size, and render the N95 useless?

Here’s what I wrote in an earlier comment (lots of good info getting buried unfortunately):

Reader Comment: I decided to do a search on the size of viruses vs. the stated efficiency of N95 masks.  Per the FDA, the N95 “respirator blocks at least 95 percent of very small (.03 micron) test particles”.

A search on the size of viruses gave me the following summary, “.004 to 0.1 microns in size, which is about 100 times smaller than bacteria”.

This is important, a little complicated, but not too much.

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Different sorts of viruses get transmitted in different ways.  The avian flu viruses are real pains in the butt because they “aerosolize.”   That’s essentially being shed as a pure virus particle that can be breathed out into the air.

These are very small particles, but not all the way as small as individual virus particles.

Here’s some data on avian transmission:

Poultry-to-human avian influenza (AI) virus transmission can occur from 3 types of exposure: fomite-contact transmission, including contact with contaminated surfaces; droplet transmission, in which large (>5 μm) particles contact a person’s conjunctiva or respiratory mucosa; and droplet nuclei transmission (or aerosol transmission), in which a person inhales small (<5 μm) particles suspended in the air.


Corona viruses, on the other hand, are not known to have the aerosolization feature.  With the one caveat that it’s always possible that the 2019-ncov is different, other known and studied cornaviruses spread mainly by droplets (>5 um).

When person-to-person spread has occurred with MERS and SARS, it is thought to have happened mainly via respiratory droplets produced when an infected person coughs or sneezes, similar to how influenza and other respiratory pathogens spread. Spread of SARS and MERS between people has generally occurred between close contacts.

(Source – CDC)

Bottom line:  N95 masks are perfectly useful for protection against other coronaviruses,  and I would expect that to be true here as well. (Of course, we’ll keep a close eye on it all in case that proves untrue).

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Also:  No mask is worth the effort if worn improperly!  Might as well not have it.  This means a snug fit where you are not breathing ‘around’ the mask.



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