CDC says double-masking improves protection from COVID-19

A woman wearing a cloth mask over a surgical mask in Arlington, Virginia, on February 8, 2021.
A woman wearing a cloth mask over a surgical mask in Arlington, Virginia, on February 8, 2021.
(Image credit: OLIVIER DOULIERY/AFP via Getty Images)

The fit of your mask matters a lot for protection against the novel coronavirus, according to a new study from the Centers for Disease Control and Prevention (CDC). And double masking may be one simple way to get a better fit, the study found. 

Although a number of medical experts — including Dr. Anthony Fauci, chief medical adviser on COVID-19 for the Biden administration — have recommended double masking in recent weeks, the study marks the first time CDC researchers have tested the method as a way to boost protection from masks. 

The findings “highlight the importance of good fit to optimize mask performance,” the authors wrote in their paper, published Wednesday (Feb. 10) in the CDC journal Morbidity and Mortality Weekly Report. “Until vaccine-induced population immunity is achieved, universal masking is a highly effective means to slow the spread of SARS-CoV-2 [the virus that causes COVID-19],” along with other measures such as social distancing, they said.

Cloth and surgical masks are popular mask choices for the general public, while N95 respirators are generally reserved for health care professionals. However, cloth and surgical masks tend to have a looser fit than N95 masks, potentially reducing their effectiveness. 

The study researchers examined two methods for improving mask fit: wearing a cloth mask over a surgical mask — i.e. double masking; or tying knots in the ear loops of a surgical mask and tucking the extra mask material close to the face, which the researchers dub “knotted and tucked masks.”

They used mannequin dummies for their experiments, and examined how well the masks worked to block small aerosolized particles, around 0.1 to 0.7 micrometers in diameter, from reaching the dummies’ faces.

The CDC researchers used dummies for their experiments. Image A shows the dummy with an unadjusted surgical mask with large gaps on the sides; image B shows the dummy with a "double mask" (a cloth mask over a surgical mask); and image C shows the "knotted and tucked mask," in which the ear loopos of a surgical mask are knotted near the mask's edge.

The CDC researchers used dummies for their experiments. Image A shows the dummy with an unadjusted surgical mask with large gaps on the sides; image B shows the dummy with a “double mask” (a cloth mask over a surgical mask); and image C shows the “knotted and tucked mask,” in which the ear loops of a surgical mask are knotted near the mask’s edge. (Image credit: CDC)

They found that a cloth mask alone blocked 44.3% of the small particles from a simulated cough, and an unadjusted surgical mask — which had large gaps on the sides — blocked 42.0% of particles from a simulated cough. But the combination of a cloth mask over a surgical mask blocked 92.5% of the particles.

In a second experiment, the researchers used two dummies spaced 6 feet apart to test the effectiveness of these methods during simulated breathing. In an experiment in which one dummy didn’t wear a mask and the other one did, double masking reduced the wearer’s exposure to small particles by 83%, and knotted and tucked masking reduced the wearer’s exposure to small particles by 64.5%. When both dummies were wearing double masks, this reduced exposure to small particles by 96.4%; and when both dummies were wearing knotted and tucked masks, this reduced exposure to small particles by  95.9%.

The fit of a mask may be particularly important now with the rise of new coronavirus variants that are more transmissible than earlier variants. With these variants circulating, “whatever we can do to improve the fit of a mask to make it work better, the faster we can end this pandemic,” Dr. John T. Brooks, medical officer for the CDC’s COVID-19 response, told The Washington Post.

Other methods for improving fit — which were not tested in the current study but have been tested in previous research — include wearing “mask fitters” or adjustable frames that are worn over a mask and secured with ear loops or or ties at the back of the head; or wearing a sheer nylon sleeve — basically pantyhose material — around the neck and pulling it up over the mask.

The researchers note that the methods they tested may not be feasible for everyone — double masking may make breathing difficult for some; and knotting and tucking may not work for people with larger faces, because the adjusted mask may no longer fully cover their nose and mouth. 

“Continued innovative efforts to improve the fit of cloth and medical procedure [surgical] masks to enhance their performance merit attention,” the authors concluded.

 

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