Doubling up your masks can provide more protection

regulatory hurdles, the rollout of injections has been sputtering and slow – and there is not yet definitive evidence to show that shots will have a substantial effect on how fast, and from whom, the virus will spread.

Through all that change, researchers have held the line on masks. “Americans will not need to be wearing masks forever,” said Dr. Monica Gandhi, an infectious disease physician at the University of California, San Francisco, and an author on the new commentary. But for now, they will need to stay on, delivering protection both to mask-wearers and to the people around them.

The arguments for masking span several fields of science, including epidemiology and physics. A bevy of observational studies have suggested that widespread mask-wearing can curb infections and deaths on an impressive scale, in settings as small as hair salons and at the level of entire countries.

One study, which tracked state policies mandating face coverings in public, found that known COVID cases waxed and waned in near-lockstep with mask-wearing rules. Another, which followed coronavirus infections among health care workers in Boston, noted a drastic drop in the number of positive test results after masks became a universal fixture among staff. And a study in Beijing found that face masks were 79% effective at blocking transmission from infected people to their close contacts.

Recent work by researchers like Marr is now pinning down the basis of these links on a microscopic scale. The science, she said, is fairly intuitive: Respiratory viruses like the coronavirus, which move between people in blobs of spittle and spray, need a clear conduit to enter the airway, which is crowded with the types of cells the viruses infect. Masks that cloak the nose and mouth inhibit that invasion.

The point is not to make a mask airtight, Marr said. Instead, the fibers that comprise masks create a haphazard obstacle course through which air – and any infectious cargo – must navigate.

“The air has to follow this tortuous path,” Marr said. “The big things it’s carrying are not going to be able to follow those twists and turns.”

Experiments testing the extent to which masks can waylay inbound and outbound spray have shown that even fairly basic materials, like cloth coverings and surgical masks, can be at least 50% effective in either direction.

Several studies have reaffirmed the notion that masks seem to be better at guarding people around the mask-wearer than mask-wearers themselves. “That’s because you’re stopping it right at the source,” Marr said.

But, motivated by recent research, the Centers for Disease Control and Prevention has noted that there are big benefits for those who don masks as