How Much Does Wearing a Mask Protect You?


You may have heard of a new study out of Denmark that tested whether paper surgical face masks protect the people who wear them.

The study comes just a week after the CDC updated guidance on masks to say they aren’t just for the benefit of others, but they also help keep people who wear them from getting sick.

So this new study — which found that these kinds of masks don’t appear to offer a big benefit to the wearer — may feel a little bit like whiplash.

Like a lot of the science on COVID-19, this study has already been passed through the prism of the divided social moment in the U.S., with people interpreting its findings depending on their political leanings.

“Mask wearing doesn’t do a damn thing,” tweeted a conservative talk radio show host in response to the study.

But that’s not exactly what the study found. And the bottom line is that you should still wear a mask.

“Masks bring down the community viral load. There’s less getting out, and that means there is less for you to be exposed to,” says John Brooks, MD, a medical epidemiologist in the Division of HIV/AIDS Prevention at the CDC in Atlanta.

In countries where mask use is high, case counts are low. That’s been true throughout history, too. Masks have long been deployed during outbreaks of infectious disease and have been shown to help control the spread of airborne germs.

But Brooks and other experts say the new study is important because it was well-done and it adds to what we know about the population-wide use of masks to control the spread of an airborne disease.

For some background, for several months now, conservative influencers have been pointing to the Danish mask study,Danmask, as proof that the pandemic and the non-drug measures that public health experts have advised us to follow — like mask-wearing and social distancing– are unnecessary and too restrictive. The study wasn’t being published, they said because the editors at scientific journals were afraid to make its findings public.

The study was published Wednesday — and made available for free, as much of the research on COVID-19 has been, by a very respected scientific journal, the Annals of Internal Medicine.

The editor-in-chief of that journal, Christine Laine, MD, co-authored an editorial that’s running alongside the study.

Asked if she’d been afraid to publish the study, Laine said, “Afraid is probably not the right word.”

“We thought it was important to publish it, but we were concerned about the risk that people who did not carefully consider the question that this trial was able to answer would misinterpret it, either because they didn’t understand the study or purposefully to support their own beliefs about the effectiveness of masks.”

The study is important because it is the first of its kind. It’s the only time researchers have been able to test mask-wearing in a randomized controlled trial, which is the gold standard for scientific evidence.

Mask-wearing is considered protective now, but in Denmark in the spring, it wasn’t routine or even advised by public health authorities. If it had been, says lead study author Henning Bundgaard, PhD, a cardiologist at Copenhagen University Hospital, the study might not have been ethical, since it would have deprived one group of participants of a recognized layer of protection against a potentially deadly virus.

“So we had a golden opportunity to do the study during this period of time,” he says. Instead of potentially putting one group in harm’s way, they were actually putting some of their participants in a better position by having them wearing masks.

“It should give some pause to people who feel kind of invincible because they go out and spend $40 on some mask designed by NASA scientists or something,” Laine says, poking fun at some of the ads she says pop up in her Facebook feed. “They may feel like they can go to a crowded setting, you know, but, ‘I’m wearing a mask, so I’m fine.’ You’re probably not fine,” she says. “You are not invulnerable to infection.”

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