Wearing two fitted masks may double protection against COVID-19: Study
Wearing two tightly-fitted face masks can double the effectiveness of filtering out SARS-CoV-2-sized particles, preventing them from reaching the wearer's nose and mouth and causing COVID-19, according to a study.
The research, published in the journal JAMA Internal Medicine, shows that the reason for enhanced filtration is not so much adding layers of cloth, but eliminating any gaps or poor-fitting areas of a mask.
'The way medical masks fit our faces isn't perfect'
"The medical procedure masks are designed to have good filtration potential based on their material, but the way they fit our faces isn't perfect," said Emily Sickbert-Bennett, an associate professor at the University of North Carolina (UNC) in the US, and the study's lead author.
Researchers wore a combination of masks to test their efficiency
To test the fitted filtration efficiency (FFE) of a range of masks, the team of researchers filled a 10-foot by 10-foot stainless steel exposure chamber with some small salt particle aerosols.
The researchers also wore a combination of masks in order to test how effective they were at keeping the particles out of their breathing space.
Particle concentration entering the breathing space was measured
Each individual mask or layered mask combination was fitted with a metal sample port attached to tubing in the exposure chamber that measured the particle concentration entering the breathing space underneath the researcher's mask. A second tube measured ambient concentration of particles in the chamber.
Researchers determined FFE with a range of activities
The researchers determined FFE by measuring particle concentration in the breathing space underneath the mask compared to that in the chamber.
"We had researchers in the chamber undergo a series of range-of-motion activities to simulate typical motions a person may do throughout their day - bending at the waist, talking, looking left, right, up and down," said Phillip Clapp from UNC School of Medicine.
Procedure mask 40-60 percent effective at keeping COVID-19-sized particles out
According to their findings, the baseline FFE of a mask differs from person to person, due to each individual's unique face and mask fit. "Generally, a procedure mask without altering the fit is about 40-60 percent effective at keeping COVID-19-sized particles out," the researchers said.
Snug-fitting, sleeve-type masks improve filtration efficiency
"A cloth mask is about 40 percent effective," they said.
Their latest findings on doubling of face masks show that when a cloth mask is placed over a surgical mask, the FFE improved by about 20 percent.
The filtration efficiency improved even more with a snug-fitting, sleeve-type mask, such as a gaiter, according to the researchers.
FFE improves by 16% with procedure mask worn over cloth
When layered over procedure masks, cloth masks improve fit by eliminating gaps and holding the procedure mask closer to the face, consistently covering the nose and mouth.
When a procedure mask is worn over a cloth mask, FFE improved by 16 percent.
"We've found that wearing two loosely fitted masks will not give you filtration benefit that one, snug-fitting procedure mask will," Sickbert-Bennett said.
For effective mask-wearing, ensure the best kind of double-masking: Sickbert-Bennett
"And with the current data supporting how effective mask-wearing is at preventing the spread of COVID-19, the best kind of double-masking is when you and the person you are interacting with are each correctly wearing a very snug-fitting mask," she added.