Are two face masks better than one? Here's what researchers say.

https://www.advisory.com/daily-briefing/2021/01/15/double-masks

January 15, 2021

"As cases of the new coronavirus continue to surge on a global scale, some of the nation's most prominent people," such as President-elect Joe Biden, "have begun to double up on masks," Katherine Wu writes for the New York Times—"a move that researchers say is increasingly being backed up by data."

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Throughout the epidemic, researchers specializing in everything from epidemiology to physics have held firm on their support for masking, Wu writes. She cites multiple studies on the efficacy of masking amid the pandemic, including several observational studies indicating that "widespread mask-wearing can curb infections and deaths on an impressive scale," another study that "found that known [novel coronavirus] cases waxed and waned in near-lockstep with mask-wearing rules," and yet another that found "face masks were 79 percent effective at blocking transmission from infected people to their close contacts."

Still more recent work is "pinning down the basis of these links on a microscopic level," Wu writes. Citing Linsey Marr, an expert on virus transmission at Virginia Tech, Wu explains the "fairly intuitive" science: The novel coronavirus and other respiratory viruses, which travel via "blobs of spittle and spray, need a clear conduit to enter the airway"—airways which masks can protect by inhibiting that potential infection. In fact, Wu writes, experiments have found that even fairly rudimentary masks, such as cloth coverings, are at least 50% effective at diverting "inbound and outbound spray."

The research has led some to begin layering masks for extra protection. If you start layering masks, "you start achieving pretty high efficiencies," Marr said. She explained, "The air has to follow this torturous path. The big things it's carrying are not going to be able to follow those twists and turns" through the obstacle course created by the mask fibers.

Overall, according to Wu, N95 masks, which provide "ultrahigh filtration efficiency" are considered the best masks—but while those are in short supply due to demand among health care providers, doubling-up on "two less specialized masks … can provide comparable protection." Specifically, Marr advised people to wear first a surgical mask, which have good filtering capabilities, and then add on a cloth mask, which tend to fit more snugly than surgical masks alone. Alternatively, she said, people can wear cloth masks stuffed with a filtering material.

But there is a point of diminishing returns, Wu writes. "[W]earing more than two masks, or layering up on masks that are already very good at filtering, will quickly bring diminishing returns and make it much harder to breathe normally."

And people can make other adjustments to improve fit and efficiency, Wu added, such as using masks that tie around the back of the head rather than looping over the ears, which can create gaps. Similarly, finding masks with nose bridges can help users wear them more tightly. As Monica Gandhi, an infectious disease physician at the University of California-San Francisco, explained, cobbling together an exceptionally well-fitting and well-filtering mask "is really simple. It doesn't need to involve anything fancy."

That said, experts cautioned that wearing masks doesn't negate the need to maintain physical distance from others and practice good hygiene. "We have to be honest that the best response is one that requires multiple interventions," Jennifer Nuzzo, a public health expert at Johns Hopkins University, said.

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