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Double Masking for COVID-19: Are two face masks better than one?

By Michelle Crouch, AARP, January 25, 2021

Experts suggest ways to add layers of protection against the coronavirus

With COVID-19 cases surging and the discovery of new, faster-spreading coronavirus strains in the U.S., it might be time to double down on face masks — literally — by wearing two at a time. Layering one mask over another can significantly boost your protection against the coronavirus, some experts say, especially if your ordinary mask is thin or loose-fitting.

"A mask is like an obstacle course for particles to get through,” said Linsey Marr, an expert in virus transmission and a professor of civil and environmental engineering at Virginia Tech. “Adding a second mask adds another obstacle course, increasing the chance that the particle will be trapped before it gets through to the other side."

Marr especially recommends use of a disposable, non-woven mask underneath a tightly fitted cloth mask, which she said should block about 90 percent of infectious particles.

Although COVID-19 vaccination has started, masking is still important because the virus will continue to spread and sicken people until most of the population is immunized. And with the discovery of new variants that could be up to 70 percent more transmissible, some experts say it's prudent to wear not just any face covering, but a high-quality one (or two).

"Last year, we wanted to get as many people to wear masks as possible,” Marr said. “This year, with new, more transmissible variants, we really need to think about improving our masks.”

All masks are not created equal

Many Americans have been wearing the same cloth masks for months — in many cases, homemade versions originally created to ease a limited supply. These days, however, there are hundreds of options for sale, including non-medical disposable surgical masks, and cloth versions with multiple layers and special filters.

Studies show that not all masks are created equal; construction, materials and fit make a difference.

"When I think of who I want to wear a mask with increased fit and filtration, I think of older adults and vulnerable people with underlying conditions,” said Monica Gandhi, M.D., an infectious disease doctor and professor of medicine at the University of California, San Francisco.

Gandhi and Marr wrote a recent commentary in Cell Press with recommendations about how to improve the protection you get from your mask.

Other countries have already taken steps to get people to wear higher-quality masks: Hong Kong distributed six-layer masks to all of its citizens; Austria sent high-grade medical masks (the equivalent of N95s) to residents over age 65; and Germany recently began mandating medical-grade masks in shops and on public transit.

The U.S. Centers for Disease Control and Prevention (CDC) says medical-grade surgical masks and N95s, the gold-standard masks in the U.S., still need to be reserved for health care personnel because they are in short supply.

A CDC division that oversees medical devices is working to develop filtration standards that will allow masks to include a label showing how well they block infectious particles. That work is expected to be completed by April, a spokeswoman said.

In addition, some U.S. scientists are calling on the federal government to increase production of medical-grade masks and make them more widely available.

Masks to Avoid

The CDC recommends against the following types of masks:

  • Masks that do not fit properly (too loose or with large gaps)

  • Masks made from loosely woven fabric, such as fabrics that let light pass through

  • Masks with one layer

  • Masks with exhalation valves or vents

  • Scarves or ski masks worn as a mask

  • Masks made from materials that are hard to breathe through (such as plastic or leather)

How to build a better face mask

For now, experts say you can still get excellent results from the cloth and non-medical surgical masks that are widely available. For a high level of protection, they offer the following suggestions:

Wear a disposable mask under your favorite cloth mask.

Start with double masking. You can maximize the protection your cloth mask offers simply by wearing a non-woven disposable mask under it, Marr said.

Most disposable masks on the consumer market are not medical grade, but they are still made of polypropylene, a non-woven fabric that electrostatically repulses viral particles. That means they should still score high marks when it comes to blocking the virus, Marr said. The problem is, their loose fit leaves too many gaps where viral particles can get in and out when worn alone.

"By themselves, surgical masks don't work great because they're so open on the sides,” Marr said. “If you put a tight-fitting cloth mask over it, that helps hold it down and reduce gaps to improve the fit.”

Marr said layering more than two masks will likely have diminishing returns as it becomes harder to breathe, making you less likely to keep them on.

Use a tightly woven cloth mask with a filter in the middle.

A snug-fitting fabric mask with a filter can block 74 to 90 percent of infectious particles, Marr's research shows. Adding a non-woven filter is important because it can help catch tiny aerosols that slip past the weave in even tightly woven fabrics.

You can buy a special HEPA filter designed to fit into a mask with a pocket, or cut up a vacuum bag. Several research studies that examine mask effectiveness have found vacuum bags to be among the best materials at catching tiny particles.

"Start with two layers of tightly woven cloth, put a plain old generic vacuum bag between them, and you've got a great blocker with effectiveness approaching that of an N95 mask,” Gandhi said.

Use hacks to make a disposable mask (or any mask) fit better.

If you usually wear a disposable mask, you can enhance the protection it offers by finding a way to tighten it so there are fewer gaps between it and your face.

For an easy fix, cross the ear loops and tuck in the corners of the mask to minimize gaps. In a Dec. 10 study published in JAMA Internal Medicine, that simple change increased a surgical mask's filtration efficiency from 38 percent to 60 percent.

Attaching the mask behind your neck with a claw hair clip or an ear guard offers a similar performance boost, the study showed, because it pulls the mask tight against your face.

You can also purchase a special mask brace or frame to go over your disposable mask and seal it against your face. A frame pushes the filtration efficiency of a surgical mask to about 80 percent, according to the JAMA Internal Medicine study.

Consider a KN95 mask.

Like N95 masks, KN95 masks are supposed to trap at least 95 percent of particles 0.3 microns in size. The only difference is that KN95s are manufactured to meet Chinese standards, rather than American ones.

KN95s were tough for consumers to find early in the pandemic because health care providers were snapping them up, but they are increasingly appearing on store shelves where ordinary shoppers can buy them. Marr said they can be a good option — as long as you're getting the real thing.

A study in September by ECRI, a nonprofit group that evaluates medical technology, found that as many as 70 percent of the KN95 masks being sold in the U.S. were counterfeit.

U.S. health officials have started testing the masks. The CDC publishes a list of the brands that did and did not meet its standards in batch tests. You may want to check the list before you buy.

In a statement, a CDC spokeswoman said that even those KN95s that don't pass muster to serve as medical-grade masks “are expected to provide source control (i.e., protect others) similar or better than gaiters, homemade, and most unregulated masks."

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