The evolving science of face masks and COVID-19

Since the Centers for Disease Control and Prevention (CDC) began recommending that members of the public mask up last spring, additional research has backed the use of face masks to combat the coronavirus. While knowledge gaps still remain, experts agree that masks should be used—and increasingly, they are emphasizing the use of better masks.

Young child’s face covered in a face mask covered in cartoon foxes.

In a review into the research on masks in April 2020, the team explained that there were some lab studies that supported the idea that masks would be effective against the coronavirus, or SARS-CoV-2. But direct evidence that face masks prevent transmission of respiratory viruses in a community was limited. In some ways, that basic takeaway hasn’t changed much.

The CDC issued new recommendations in February to encourage people to improve the fit and filtration of their masks. Drawing on the findings of lab experiments, the agency suggested layering a cloth mask over a disposable one—a form of “double masking”—or using a mask fitter or brace, among other options.

Over the last year, additional research has generally supported the notion that face masks can reduce transmission of the virus, although proof is still lacking.

Numerous lab studies, for example, show that masks can partially block exhaled respiratory droplets, which are thought to be the primary way the virus spreads—and may offer some protection to the wearer.

In one study, scientists at the CDC’s National Institute for Occupational Safety and Health tested a variety of face coverings for their ability to prevent the outward spread of particles from a simulated cough. N95 respirators performed the best—blocking 99% of the particles—while medical masks blocked 59% and a cloth mask blocked 51%. The only covering that failed to do much of anything was a face shield, which stopped just 2%.

In another experiment, researchers in Japan evaluated how well different masks on two mannequins that faced one other reduced exposure to the coronavirus. Cotton or surgical masks on the mannequin releasing the virus cut the amount of exposure to the other by 50% or more. If only the exposed mannequin wore such a mask, the protective effect was smaller, but if both wore a mask, transmission decreased by 60% to 70%.

This story is by Jessica McDonald.