Cloth Masks Reduce Wearer's Exposure To Cough Particles By 77%

LOS ANGELES, CA — Even the simplest cloth mask protects the wearer by reducing their exposure to cough particles by as much as 77 percent, UCLA researchers said Wednesday.

The study allowed scientists to pinpoint how much masks and face shields can protect the wearer. The findings are in keeping with this weeks update to the Centers for Disease Control guidelines on mask-wearing. The guidelines were altered to indicate that masks protect the people who wear them as well as the people around them.

"We found that a simple cough could send particles more than six feet away, without face coverings. At about a foot away from the coughing source, a face shield by itself provided the least protection (4%). In contrast, a cloth mask reduced cough particles by 77%, and the combination of face shield and cloth mask improved the particle reduction to 89%," said Yifang Zhu, a professor in the Department of Environmental Health Sciences and associate dean for academic programs at the UCLA Fielding School of Public Health.

Zhu's team, which includes UCLA scholars Liqiao Li and Muchuan Niu measured the particle number concentration (PNC) and particle size distribution under seven different conditions in a test lab. The measured conditions with (1) no face covering; (2) face shield only; (3) cloth mask; (4) face shield + cloth mask; (5) surgical mask; (6) face shield + surgical mask; (7) N95 respirator or equivalent (i.e., KN95 mask).

"To minimize the infection risk of aerosol transmission, stricter mitigation measures should be adopted for indoor environments, which are more likely to be enclosed and crowded," Li said. "One of the simplest is a mask."

Their article was published in the current edition of the peer- reviewed journal Aerosol Science and Technology, and can be viewed here.

City News Service and Patch Staffer Paige Austin contributed to this report.