FRIDAY, May 22, 2020 (HealthDay News) -- Face coverings may reduce the risk of transmitting COVID-19, a new study suggests.
Researchers assessed the effectiveness of seven types of face coverings -- including medical-grade and homemade masks -- when people breathed or coughed while standing or lying down. They were also tested using a dummy attached to a cough-simulating machine.
All face coverings without an outlet valve reduce the forward distance of a deep exhale by at least 90%, according to the study led by engineers at the University of Edinburgh in Scotland.
A respirator mask -- widely used by workers exposed to fine dust -- protects the wearer. But the study warned that valves meant to make breathing easier could allow exhaled air to spread considerable distances in front of the wearer.
"I have generally been impressed by the effectiveness of all the face coverings we tested," said study leader Ignazio Maria Viola, from the university's School of Engineering.
"However, we discovered that some face coverings allow the emergence of downward or backward jets that people are not aware of and that could be a major hazard to others around them," he said in a university news release.
Surgical and handmade masks were found to reduce the forward flow of droplets in people's breath. But they also jetted air to the side, behind, above and below. Heavy breathing and coughing, in particular, caused intense backward jets.
Only masks that formed a tight seal with the face prevented the escape of fluid particles that can carry viruses, according to the study released May 21, ahead of publication in a journal.
Full-face shields worn without masks permit the release of a strong downward jet, the researchers found.
"It was reassuring to see the handmade mask worked just as well as the surgical mask to stop the wearer's breath flowing directly forwards. This suggests that some handmade masks can help to prevent the wearer from infecting the public," said Dr. Felicity Mehendale, a surgeon at the Center for Global Health at the university.
"But," she added, "the strong backward jets mean you need to think twice before turning your head if you cough while wearing a mask; and be careful if you stand behind or beside someone wearing a mask."