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COVID-19 Resource Center

Perspective from Monica Gandhi, MD, MPH
Disclosures: The authors report no relevant financial disclosures.
February 10, 2021
2 min read
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CDC says double masking offers more protection

Perspective from Monica Gandhi, MD, MPH
Disclosures: The authors report no relevant financial disclosures.
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CDC researchers tested two modifications that they said “substantially” improved the effectiveness of surgical masks as protection against SARS-CoV-2, including double masking — wearing a cloth mask over a surgical mask.

The other modification involved knotting the ear loops of a surgical mask near the mask’s edges and tucking in the extra material (see panel C here).

CDC mask infographic
Testing shows that double masking or knotting and tucking medical masks significantly improved fit and filtration, lessening exposure of wearer and individuals around the wearer.
Credit: CDC

“Controlling SARS-CoV-2 transmission is critical not only to reduce the widespread effects of the COVID-19 pandemic on human health and the economy but also to slow viral evolution and the emergence of variants that could alter transmission dynamics or affect the usefulness of diagnostics, therapeutics, and vaccines,” John T. Brooks, MD, a medical epidemiologist on the CDC’s COVID-19 Emergency Response Team, and colleagues wrote.

“The data in this report underscore the finding that good fit can increase overall mask efficiency,” they wrote. “Multiple simple ways to improve fit have been demonstrated to be effective. Continued innovative efforts to improve the fit of cloth and medical procedure masks to enhance their performance merit attention.”

Brooks and colleagues conducted various experiments in January to assess the two methods. In the first experiment, they used a pliable elastomeric head form to simulate a person coughing in order to test the effectiveness of various mask combinations to reduce particles emitted during a cough (source control). The second experiment assessed how effectively the two modifications to medical procedure masks — for example, surgical masks — reduced exposure to aerosols emitted while breathing.

Results from the first experiment demonstrated that the unknotted medical procedure mask blocked 42% of particles from a simulated cough on its own, whereas the cloth mask blocked 44.3%. They found that combining the masks blocked 92.5% of the cough particles.

Results from the second experiment showed that adding a cloth mask over the medical procedure mask or knotting and tucking the medical procedure mask reduced exposure of an unmasked receiver by 82.2% and 62.9%, respectively.

Brooks and colleagues said that when the source was unmasked and the receiver was fitted with the double mask or the knotted and tucked medical mask, the receiver’s exposure was reduced by 83% and 64.5%, respectively, and when the source and receiver were both double masked or using knotted and tucked masks, the exposure of the receiver was reduced 96.4% and 95.9%, respectively.

There were drawbacks to both modifications, the researchers noted, including that “double masking might impede breathing or obstruct peripheral vision for some wearers, and knotting and tucking can change the shape of the mask such that it no longer covers fully both the nose and the mouth of persons with larger faces.”

“We continue to recommend that masks should have two or more layers, completely cover your nose and mouth, and fit snuggly against your nose and sides of your face,” CDC Director Rochelle P. Walensky, MD, MPH, said during a White House press briefing.