Even a simple cloth mask provides significant protections against COVID-19 transmission, reducing the spread of respiratory droplets by as much as 77%, UCLA researchers said Wednesday.

“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, set up a test space in a lab and measured the particle number concentration (PNC) and particle size distribution under seven different conditions: (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 at www.tandfonline.com/doi/full/10.1080/02786826.2020.1846679.

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