New Study Confirms Face Shields and Valve Masks Can’t Be Trusted

Visualizations reveal these substitutes don’t measure up

A laser-illuminated horizontal and vertical cross-section of droplets escaping a face shield 16.6 seconds after a simulated cough. Image: Siddhartha Verma, Manhar Dhanak, John Frankenfield, Florida Atlantic University

Frustrated with the discomfort of face masks, some people have been using face shields, which have been promoted by some health experts to help prevent the spread of Covid-19. Other people are turning to masks with exhalation valves that make breathing out easier. Now, a new study based on a laboratory simulation brings into laser focus how ineffective both alternatives are at containing the coronavirus.

Face shields were touted as a possible alternative to masks in an April opinion piece in the Journal of the American Medical Association (JAMA) and in subsequent popular articles.

“We were a little surprised that they would say that,” says Siddhartha Verma, PhD, assistant professor in mechanical engineering at Florida Atlantic University and a member of the visualization research team. “And that was our motivation to show people what actually happens.”

The shield’s main job is to block splatters of fluid from the patient and can protect the wearer’s eyes, but they have not been shown to be very effective at protecting other people when worn by an…