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Two masks could be one too many

Experts say double masking is a double-edged sword.

A legislator in Mississippi adjusted her two face masks while asking a question in a hearing.
A legislator in Mississippi adjusted her two face masks while asking a question in a hearing.Rogelio V. Solis/Associated Press

The Centers for Disease Control now says you’re better off doubling up on certain kinds of masks. But after talking to several experts and examining the research, I’m sticking with one mask for now — one that fits well and has several layers — and I fear the CDC’s recommendation is confusing. Here’s why.

Cloth masks are now like Legos and toy vehicles, the kind of thing I find in every nook of my home. My kids and I have been trying out masks for the product review site Wirecutter since last July, and I’ve been closely following mask research and policies since the start of the pandemic.

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When headlines about double masking began circulating, I wondered whether it was sound policy. It’s true that two masks can, theoretically, trap more virus-containing droplets than one. But filtration is not the only thing that matters when wearing a mask or persuading someone else to wear one; fit, breathability, and comfort are just as important.

The CDC study that was the basis for its recent suggestion to double up on certain masks has limitations, says Taher Saif, an engineering professor at the University of Illinois who has led research on cloth mask performance. One of its shortcomings, he says, is that it didn’t take into account breathability.

There has to be a balance between filtration and breathability in order for a mask to work well, Saif explains. For example, you could make a mask out of aluminum foil, and it would block everything from coming through it. But unfiltered air would just come around the sides. What matters is the number and quality of layers, plus the fit.

According to Saif, some mask studies, like the CDC’s latest, don’t quite replicate how a mask works on someone’s face. Many of these lab tests push a continuous flow of particle-containing air through a hole that’s covered by a mask, which is not like someone breathing in and out, he says. In reality, if a mask doesn’t fit, or isn’t worn properly, or has large gaps, or if air doesn’t pass through the mask when a person is inhaling and exhaling, it is going to be less effective.

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Because of all this, Saif worries that in the real world wearing two masks could be less effective if they’re too hard to breathe through.

Martin Fischer, a chemistry professor at Duke University who has studied mask efficacy, says poorly performing masks, like a neck gaiter or thin cotton mask, would benefit from being doubled up. But wearing two good masks is counterproductive, he says, because if together they are too dense, the air will go around gaps rather than through the mask.

Another problem is that there are now people turning to Twitter to claim that the CDC’s new guidelines about wearing two masks are “proof” that wearing one mask is ineffective and that mask mandates are pointless. But there’s plenty of evidence that wearing a mask, even a cloth one, is effective.

“There’s potential here of making the perfect the enemy of good,” says Benjamin Linas, an epidemiologist at Boston University. “It would be better to have everyone wearing a comfortable single mask than for some people to be double masking.”

Jennifer Balkus, a professor of epidemiology at the University of Washington, says the government ought to concentrate on increasing the availability of good masks. “By asking people to double mask in certain scenarios, you’re putting that burden of intervention on an individual, rather than providing individuals with a better mask,” she says.

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Based on current evidence, and what he knows from many months of research in his lab and other studies in the field, Saif is sticking with a single two-layer cotton mask. Fischer, too, will continue to wear one mask at a time — a surgical-style mask when he goes to the store, and a cloth mask when he’s in his lab and able to social distance. Comfort is important, Fischer says, and he’d rather people wear a good single mask properly.

Same with me and my family. There have been enough challenges during the pandemic, and since we’ve all found our favorite masks, I’m reluctant to upend our masking routine without more evidence. Now I just need to go hunt for that dinosaur mask.

Christina Szalinski is a freelance science writer with a PhD in cell biology.