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Double-masking the right way

ASU aerosol expert Pierre Herckes provides advice on this new practice


Pierre Herckes

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March 11, 2021

Double-masking, or wearing one mask over another, has been the subject of much recent media attention. Even as COVID-19 rates decline, state and federal agencies recommend continuing to wear masks. If one mask is good, wouldn’t two be better? Not necessarily, especially if the masks are worn incorrectly.

Arizona State University mask expert Pierre Herckes gave advice during a recent interview with the Las Vegas Review-Journal.

“Incorrectly wearing a double-mask can lead to higher exposure,” Herckes said.

Higher coronavirus exposure can occur if the masks do not fit properly. 

“For masks, it is all about the fit so that air gets filtered through your mask rather than going around your mask,” Herckes said.

For this reason, Herckes advises against doubling up on surgical masks because adding a second mask increases resistance through the mask which increases air leakage around it.

Instead, Herckes said, “The proper technique is to wear a surgical mask covered by a cloth mask.”

This increases the amount of filtration without too much resistance, and the cloth mask can help push the surgical mask against the face, giving it a better fit.

KN95 (or N95) masks should not be worn with a second mask. These masks fit well if worn correctly and by adding resistance will likely result in air bypassing the mask, which decreases its effectiveness. A properly fitted KN95 (or N95) mask is still superior to double-masking.

Double-masking can be a benefit, but only when done properly. Proper fit is key for any mask to be effective. To keep masks effective, they must also be handled and disposed of properly.

“It’s also important to not reuse masks that aren’t designed for multiple uses,” Herckes said. 

Surgical masks are single-use, and cloth masks should be washed regularly. COVID-19 cases are decreasing, and proper masking continues to play an important role.

“Pierre has been doing excellent research in an easily overlooked aspect of COVID research, specifically, air dispersal of the virus and personal protection," Ian Gould, interim director of the School of Molecular Sciences said. "Here in (the school) we have relied on Pierre as a local expert to provide guidance on mask use and other ways to keep our staff, students and faculty safe during the crisis.”

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