On Feb. 10, the Center for Disease Control released new guidelines for masking. Based on a study conducted in January, the CDC now recommends fitting a cloth mask over a surgical mask to reduce COVID-19 transmission.
According to the CDC, the study used “a pliable elastomeric headform . . . to simulate a person coughing by producing aerosols from a mouthpiece.” A variety of face masks were then placed on the headform to measure their effectiveness.
The data showed that a cloth mask layered over a surgical mask blocked 85.4% of cough particles whereas a single medical mask or cloth mask blocked only 56.1% and 51.4% of particles, respectively. When both the cougher and receiver were double masked, the risk of exposure dropped to 96.4%.
However, not all masks should be layered. According to their website, the CDC does not recommend layering n95 respirators with cloth masks or surgical masks since they already “provide a reliable level of protection against airborne or aerosolized particles.”
Christopher Hamilton, professor of biochemistry, stressed that there are no negative effects of double masking.
“Certainly, if you are going to have greater filtration, it is going to be harder to breathe,” said Hamilton. “If someone does have asthma or COPD, it could definitely cause fatigue much faster. But in the long term, even for those people, there are no negative health consequences.”
Hamilton also emphasized that if a double mask feels uncomfortable, certain measures can be taken to improve wearability without sacrificing function.
“If masks are tight fighting, they recommend plastic braces under the mask. The problem is that masks can get right up under the nose and mouth and feel claustrophobic, but the brace gives you a gap of space at your nose while keeping the mask sealed.”
Certain types of n95 masks which fit snugly to the face while maintaining space at the nose and mouth also work well to improve comfortability, added Hamilton.
In the January study, the CDC also sought to compare the effectiveness of a single, tightly-fitted mask to layered masks. Data showed that a surgical mask with knotted earloops blocked 77% of cough particles, 7.4% percent less than the combination of a cloth and surgical mask.
Following the CDC study, researchers at the University of North Carolina at Chapel Hill came to a different conclusion. While they stressed that wearing two masks is certainly an improvement to wearing one, they found that a mask’s fit remains the most important factor in reducing COVID-19 transmission.
“You really need to address fit and make sure whatever you’re wearing is tight to your face,” said Phillip Clapp, an aerosol toxicology expert at the UNC School of Medicine, in a press conference last Friday.
Clapp and his colleagues found that simply wearing a cloth mask over a surgical mask increased filtration by 15% while a single, well-fitted mask increased filtration by 20%. Still, Clapp added that the best precaution is wearing a cloth mask over a tightly knotted surgical mask.
Despite the new research, the White House has yet to recommend double masking to the public. So far, only New York has imposed any sort of double masking mandate.
