If One Mask Is Good for COVID Protection, Are Two Better?

Based on recent test results, the Centers for Disease Control and Prevention (CDC) in February recommended double-masking to reduce the risk of COVID-19 viral transmissions.

For the record, “double-masking refers to wearing both a surgical mask and a cloth mask over the surgical mask,” says Paul Drain, MD, MPH, associate professor of global health, medicine (infectious diseases), and epidemiology at the University of Washington. He is the principal investigator of several studies into COVID-19 diagnoses. “The use of a disposable mask under a cloth mask has been shown to improve protection in a lab study, and this has been detailed on the CDC website,” Drain says. “Here the role of the cloth mask is mostly to push the surgical mask tight against the skin.”

“EMTs and paramedics go in and out of private residences—places where people who potentially have the virus have been inside inhaling and exhaling,” says Linda Yancey, MD, an infectious-disease expert with the Memorial Hermann health system in Houston. “So they have the potential to be going into places with fairly high numbers of virus [particles] in the surrounding air. The more layers of protection they can put between themselves and that air, the safer they’re going to be.”

The CDC Report

In a February document entitled “Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021,” the CDC reported on two experiments into double-masking and other techniques aimed to reducing virus transmissions. (Read the report here.)

“Results from the first experiment demonstrated that the unknotted [three-ply] medical procedure mask alone blocked 56.1% of the particles from a simulated cough (standard deviation [SD] = 5.8), and the [three-ply] cloth mask alone blocked 51.4% (SD = 7.1),” said the CDC report. “The combination of the cloth mask covering the medical procedure mask (double mask) blocked 85.4% of the cough particles (SD = 2.4).”

In the second experiment, where a source head form (emitting virus particles) and a “receiver” were used, “adding a cloth mask over the source head form’s medical procedure mask…reduced the cumulative exposure of the unmasked receiver by 82.2%. (SD = 0.16). When the source was unmasked and the receiver was fitted with the double mask…the receiver’s cumulative exposure was reduced by 83.0% (SD = 0.15).”

Making Sense of It

The fact that the CDC tested a combination of three-ply paper and cotton masks is critical to evaluating the usefulness of its data for EMTs and paramedics.

The value of this proposition is based on the fact that “all masks are not created equal,” says Yancey. “If you have folks in cotton masks with only one or two layers of fabric, those just don’t offer the same kind of protection that big, padded masks or N95 masks will grant you. So if you’re wearing a paper surgical mask or a thin cotton mask, there is a good deal of benefit to adding a second mask on top of that. It just provides more layers of material between your respiratory tract and potential viruses, giving them less of an opportunity to be inhaled into your nose and lungs.”

At the same time, “double-masking does not apply to N95 masks, which filter out 95% of small particles from the air and have been reserved for healthcare workers,” says Drain. “Double-masking has been advised for some community members who may be at sustained and high exposure.”

It is for this reason that “Seattle Fire is not double-masking in any official way as an EMS organization, though it’s likely that many members do this off-duty,” says Brian Wallace, the SFD’s COVID-19 testing and vaccination coordinator. “This is because our members are wearing N95s on EMS runs on duty or while conducting testing.” (He added that, “We currently wear surgical masks in the stations and are seeing a very low incidence of transmission among coworkers, likely in no small part due to vaccination.”)

This said, “the most critical element is having a mask that properly fits,” says Drain. “Therefore, if EMTs/paramedics are using N95s, they should be properly fit-tested. For EMTs/medics who may not have access to N95s, then KN95 (the standard in China) would be suitable or using a well-fitted surgical mask would be sufficient.”

More Is Not Always Better

There is one last thought to pass on with respect to the CDC report on double masking: Just because two masks combined can provide better protection against COVID-19 transmission doesn’t automatically mean layering multiple masks on top of each other is a good idea.

“There is a limit—you don’t want to stack on five masks because you actually want to be able to keep on breathing,” says Yancey. “You still have to have the air being able to flow easily in and out through the mask rather than around the sides, because that kind of defeats the purpose.”

James Careless is a freelance writer and frequent contributor to EMS World.