Scientists actually randomized people to wear N95 or regular surgical masks, then tracked how many people became infected with colds and flu. The results surprised me.
people's intuition
The results are surprising as I have seen many people claiming that we need N95 masks to stop the virus. They say surgical masks won't cut it.
And to be honest, this is my intuition as well. N95 masks are much tougher than surgical masks, and they capture a higher percentage of particles. They are what I wear in Delhi and Beijing.
test
The scientists tested this question by randomly assigning more than 2,000 nurses to wear N95 or surgical masks. Then they tracked how many of those people caught the flu.
I polled Twitter users to see what people's intuitions are. The majority (68%) guessed N95, so I'm not alone in my intuition.
But when the data came back it was found that the infection rate was the same!
The differences were not significant, although surgical mask users actually had slightly lower infection rates.
ok maybe that was a fluke
The data can be temp-y. It is just a study. But it is not the only one.
Researchers in Canada randomly assigned 446 nurses to wear N95 or surgical masks during certain months of cold and flu season (September through December). They then tracked how many people had had the flu or cold.
Again, no significant difference! A total of 9.4% of nurses wearing surgical masks fell ill, while 10.5% were sick wearing N95 masks.
totally justified skepticism
At this point, at least some knowledgeable readers may be thinking, "Ah!"
I know what's going on! These studies compared people wearing different types of masks, but all were wearing some kind of mask. So we don't know if the masks actually work. If both masks don't work, there's definitely no significant difference!
This is a great question. It's hard to test because, what are we going to do? Assign nurses not to wear masks? It seems irresponsible.
We need some situation where people face infection but don't normally wear masks. It turns out, scientists found just such a place:
House!
no-mask test
Researchers in Australia studied parents caring for their children who were sick with the flu.
Because people often don't wear masks at home (even around sick people), researchers can defensively randomly assign people to wear or not to wear a mask. They randomly assigned parents to wear no masks, surgical masks, or N95 masks, as I'm wearing here.
Then they tracked how many parents got the flu.
Overall, 17% of parents became ill. But the infection rate was 5% in parents wearing surgical masks and 4% in parents wearing N95 masks (here called "P2" masks).
Thus, the masks went to work! They worked again when researchers in Germany tried the same thing:
But the mask did not guarantee 100% protection. And again, surgical masks were just as effective as N95 masks.
Perhaps not surprisingly, masks only worked for people who actually wore them. There was no use among those who often forgot or simply stopped wearing masks. No shockers there! To be effective, you have to actually wear it.
How on earth could surgical masks and N95 masks work?
Well, at this point, there must still be some skeptical readers out there. There is no way surgical masks can capture particles so small! I saw a doctor on Quora saying that "most masks" cannot capture virus-sized particles.
Similarly, NPR reported that surgical masks only capture larger droplets:
But none of them actually cite the data. My guess is that they are citing their own intuition. If we ignore our intuition and look at the actual test data, the reality is far more interesting. Trial data shows that surgical masks are surprisingly effective for even small particles. For example, in one study, researchers tested particles down to .007 microns (even smaller than a virus) and found that a simple surgical mask blocked 80%.
Still, the N95 and N99 masks outweigh them. For example, in that study, N95 masks captured 96% (see also 1).
So it's amazing that surgical masks are just as effective! Maybe virus particles are actually easier to catch because they usually fly on droplets of water. Or maybe masks to help prevent people from touching their mouth and nose. For now, I can only guess.
Bottom Line: There is scientific evidence that (1) masks prevent flu infection and (2) surgical masks prevent infection as well as more sophisticated N95 masks.
Breathe Safe!
PS What Materials Work Best for DIY Masks?
Smart Air's nerd squad took 30 seconds to make a DIY mask
Tested more materials. Here's what worked best:
The Ultimate Guide to Homemade Face Masks for Coronavirus
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