Double Masks Offer Significantly Better Protection, CDC Study Finds
By
Betsy McKay
Wearing a three-ply cloth mask over a three-ply medical or surgical mask blocked more than 90% of particles from a cough.MARK MORAN/ASSOCIATED PRESS
Upgrading your mask can really make a big difference, according to a study published Wednesday by the Centers for Disease Control and Prevention.
Wearing a double mask or fitting a single mask more closely on the face substantially reduces the risk of infection with the Covid-19 virus, the study,
published in the agency’s Morbidity and Mortality Weekly Report, found.
In a series of laboratory experiments using headforms and machines to generate aerosols, the CDC found that wearing a three-ply cloth mask over a three-ply medical or surgical mask blocked 92.5% of particles from a cough.
That was much more effective than a single mask. A surgical mask alone blocked cough particles by 42%, and a cloth mask blocked them by 44.3%.
Many medical and engineering experts say
people need to upgrade their masks because new variants of the virus are
spreading around the country, particularly one that is
significantly more transmissible than the currently most common strain. Other studies have shown benefits from
wearing double masks or using mask fitters, devices which tighten the fit.
Still other experts say that people should wear N95 masks, which are used primarily in hospitals and are certified to filter out at least 95% of small particles.
The CDC is trying to accomplish two goals: convince people to wear a mask at all--since many aren’t doing that currently--and offer options on its website that can help them improve or find a good fit, said John Brooks, chief medical officer of the agency’s Covid-19 response.
“Masking is one of our
most potent means for not only the epidemic and its effects on human health and the economy, but also for slowing viral evolution,” he said. “We are looking at all the ways we can enhance our prevention measures.”
It isn’t known whether the performance of single or double masks is different against the new variants, Dr. Brooks said. “It’s the same virus, so the measures should work,” he said. “What we don't know is how effectively they will work.”
In the lab experiments, the double mask was also more protective against aerosols from breathing. It blocked 83% of aerosols emitted during 15 minutes of quiet breathing by an unmasked headform in a small room. The protection was 96.4% when the other person in the room was also wearing a double mask or a close-fitting single mask, the study found.
The CDC also tested the effectiveness of a medical or surgical mask that was better fitted by tying knots in the ear loops and tucking the sides in close to the face. Wearing that mask blocked 64.5% of aerosols emitted by the other headform, which was unmasked, and 95.9% of the particles when the headform was masked.
“Whatever we can do to improve the performance of masks right now will speed our control of this pandemic,” Dr. Brooks said
