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CDC: 2 Face Masks Protect Better Than One

How to upgrade your mask to protect against the coronavirus

Watch: How and Why to Double-Mask

En español | With 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 a cloth mask over a disposable medical procedure mask significantly boosts your protection against the coronavirus by ensuring a tighter fit against your face, a new study from the U.S. Centers for Disease Control and Prevention (CDC) shows.


The CDC study also showed that you can substantially improve the performance of a surgical mask by knotting the ear loop strings where they meet the mask and tucking in mask edges. That eliminates gaps on the sides. 

Following the release of the study, the CDC published new guidance on how to improve your mask that emphasized the importance of fit. “Make sure your mask fits snugly against your face,” the CDC says. “Gaps can let air with respiratory droplets leak in and out around the edges of the mask.” 

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 even more 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 nonmedical 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 co-authored a commentary in Cell Press on Jan. 15 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.

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.


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How to build a better face mask

For now, the CDC and infectious disease experts say you can still get excellent results from the cloth and nonmedical 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. CDC researchers found that wearing a single mask – cloth or surgical – blocked only about 42 to 44 percent of particles from a simulated cough.  However, when a cloth mask was worn over a surgical mask, 92.5 percent of cough particles were blocked.

Most disposable masks on the consumer market are not medical grade, but they are still made of polypropylene, a nonwoven fabric that electrostatically repulses viral particles. That means they 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.”

The CDC does not recommend layering two disposable masks because “they are not designed to fit tightly, and wearing more than one will not improve fit.”

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 nonwoven 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.

Make sure you have a good fit

The CDC makes the following recommendations to improve mask fit:

  • Choose a mask with a nose wire, which prevents air from leaking out along the top. Bend it to fit close to your face.

  • Use a mask fitter or brace over a disposable or cloth mask to prevent air from leaking out around the edges. These small, reusable devices cinch the mask against your face and can boost the filtration efficiency of a surgical mask to about 80 percent, according to a Dec. 10 study in JAMA Internal Medicine.

  • Make sure your mask fits snugly over your nose, mouth and chin. “If the mask has a good fit, you will feel warm air come through the front of the mask and may be able to see the mask material move in and out with each breath,” the CDC says.

  • If you wear a disposable mask, knot the ear loops where they join the edge of the mask, and then fold and tuck the unneeded material under the edges. The CDC links to video instructions at https://youtu.be/UANi8Cc71A0

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."

Do not wear another mask with a KN95, the CDC says. Wear only one at a time.

Michelle Crouch is a contributing writer who has covered health and personal finance for some of the nation’s top consumer publications. Her work has appeared in Reader’s DigestReal Simple, Prevention, The Washington Post and The New York Times.