Provided you find a mask uncomfortable — and not everyone does – face shields might appear to be a good alternative. Clear and less restrictive, they sidestep some of the annoyances of masks, allowing your face to see the light of day.
But it’s possible that comfort comes at a cost. Authors of a new scientific study want you to see if for yourself.
New research shows that face shields can catch the majority of droplets released during a cough. However, smaller aerosol-sized droplets remained suspended in the air, hovering near the bottom opening of the face shield.
After 10 seconds, those hovering droplets could spread three feet away — either in front or behind — the cougher, the paper notes. The droplets decrease in concentration, meaning that the farther out they get, the fewer of those droplets remain afloat.
The study was published Tuesday in Physics of Fluids.
Siddhartha Verma, the study’s first author and a professor at Florida Atlantic University, says the experiment is supposed to be an illustration of a simple fact: it’s possible that smaller aerosols can escape from face shields.
The fact that droplet concentration decreases as the droplets waft away underscores the importance of social distancing, he says. The fact that they escape at all reminds us that a face shield can’t replace a face covering.
That said, a face shield can augment a face mask. A face shield can reduce the chance of encountering the virus through other avenues, like the eyes, as Deborah Birx, the White House coronavirus response coordinator, advised in July.
“It’s okay to use both of them at the same time,” Verma tells Inverse. “But only a face shield is not as effective as a single mask. It helps for [people] to see for themselves how the droplets actually spread.”
Richard Flagan is a professor at CalTech who studies aerosols and was not involved with the study. He says the video is useful in that it illustrates the issues with face shields (and masks with valves, which the CDC also does not recommend).
“It will protect against the spray, but not against the aerosol,” Flagan tells Inverse.