Since almost the start of the COVID-19 pandemic in the United States, public health experts have recommended that almost everyone wear a mask in public spaces — particularly indoor spaces where it’s difficult to maintain physical distance from other people. But especially since the most protective types of masks — such as N95 masks — remain in short supply and are generally reserved for frontline workers, many people have been left to wonder how much their masks really protect against the viral infection.
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In an attempt to make their masks more effective, some people have taken to wearing two of them at once. Prominent public figures — including football coaches and politicians — have been spotted doubling up on masks. But is this strategy really effective? Here’s what experts say about how and when to layer your masks.
Blocking respiratory droplets
While some people complain about how it feels to wear a mask, standard cloth or surgical masks don’t significantly impede most people’s ability to breathe, according to a recent article in The New York Times on double masking — and that’s a very good thing. The point of wearing a mask isn’t to block the flow of air. Instead, it’s to block respiratory droplets that would normally travel with the air that you breathe out (and, to a lesser degree, in).
The more complicated the path these respiratory droplets have to take — navigating an obstacle course of cloth fibers — the more likely they are to be blocked by your mask. While there aren’t any studies so far that specifically examine double-masking, it’s clear from existing studies on masks and COVID-19 that these cloth barriers really are effective at preventing transmission of the virus.
One study, for example — published in June 2020 in the journal Health Affairs — found that statewide mask mandates reduced the growth rate of COVID-19 cases by an average of 2.0 percentage points 21 days after they went into effect. A a result, estimates suggest that just by May 22, 2020, over 200,000 cases of COVID-19 were prevented by these mandates.
Another study, published in July 2020 in the journal JAMA, found that in the Mass General Brigham (MGB) health system in Massachusetts — the largest healthcare provider in the state — a universal masking policy covering 75,000 employees at 12 hospitals that was implemented in March 2020 significantly reduced COVID-19 infections. Before this policy was put in place, the rate of COVID-19 positive test results among employees has increased from 0% to 21.32%, with an average increase of 1.16% per day. After a transition period in which the universal masking policy was implemented to cover all employees and patients, the test positivity rate among employees fell from 14.65% to 11.46%, with an average drop of 0.49% per day.
Why airflow is important
According to experts quoted in the Times article, maintaining your ability to breathe somewhat comfortably when wearing a mask — or masks — isn’t just a question of comfort. While the goal of masking is to block the flow of respiratory droplets, it’s equally important that air itself can move through. Once airflow is significantly restricted, instead of flowing through your mask, it may flow around it at the edges — carrying respiratory droplets with it, and defeating the purpose of the mask.
To increase the effectiveness of blocking respiratory droplets, experts recommend wearing a surgical mask — which blocks these particles better than most cloth masks, but can be loose-fitting — underneath a wider cloth mask that helps the surgical mask hug your face. The cloth mask also offers some extra protection, adding to the complexity of the path respiratory droplets must travel.
So until the pandemic is over, keep in mind that for situations in which you need extra protection, two masks really are better than one — as long as you can still breathe through them.