How do face shields offer protection from coronavirus?

The new coronavirus spreads mostly through droplets expelled from an infected person coughing, sneezing or talking. Face shields cover the eyes, mouth and nose—the areas of potential infection. “If someone coughs and it catches your eyes, you are going to get the infection,” says Daniel McQuillen, vice president of the Infectious Diseases Society of America and an infectious disease physician at Beth Israel Lahey Health in Boston.

Face shields block droplets, which are larger particles that drop to the floor due to gravity, but not aerosols, smaller particles that may linger in the air when exhaled during a dental procedure or intubation. “The general way that this virus spread is by droplets, despite the scary pictures you see of aerosols and things hanging in the air,” Dr. McQuillen says.

Covering Your Bases

A well-itting face shield can be a good option for additional coverage.

Fits without gaps at the forehead

Reaches to the ears

Photo:  The ClearShield by ClearVision (available on the storeforppe.com)

Cleaned with sanitizer or soap and water

What are the benefits of wearing a face shield?

Uses waterproof, clear plastic material

Shield extends below the chin

The shield covers more of the face than a mask, so infected droplets are less likely to land anywhere near your eyes, mouth or nose.

A meta-analysis that looked at nearly 26,000 patients affected by Covid-19 and similar conditions that was published in the Lancet this month found “eye protection might result in a large reduction in virus infection” and provides additional benefit to mask wearers. In health-care settings, eye protection reduced risk compared with no eye protection in 13 studies, but more evidence is needed, says co-author Derek Chu of McMaster University in Hamilton, Ontario.

And in countries including China and South Korea “PPE is starting to shift from masks to shields,” says Luis Ostrosky, professor of infectious diseases at UTHealth’s McGovern Medical School in Houston.

What scientists don’t yet know is what portion of infections start in the eyes, or whether face shields are superior to face masks.

Shields can be easier to wear for prolonged periods, especially for those with breathing problems. You may also be less likely to touch your face while wearing a shield or fidget with the shield itself, says Michael Edmond, chief quality officer at the University of Iowa Hospitals & Clinics. “Universal face shielding would help stop the outbreak and let people have less restrictions on what they do,” says Dr. Edmond, an infectious disease doctor who co-wrote an opinion piece on the community use of face shields in JAMA this April.

Should you still wear a mask under the face shield?

There’s no consensus. Infectious disease experts calling for greater adoption still disagree on whether wearing a face shield alone offers enough protection for yourself or others.

Dr. Edmond says a face shield on its own is enough to wear in most community settings, especially if keeping a social distance. “For general life, I just wear a shield,” he says. He also believes face shields alone are just as effective in preventing an infected person from infecting others.

Other experts, including Saad Omer, director of the Yale Institute for Global Health, say that face shields should be used in conjunction with masks until more research is available. “There is no harm in taking extra precautions, especially in a closed setting,” he says.

Not all doctors think shields can stop people from receiving or spreading infection, including Aaron Glatt, chairman of the department of medicine at Mount Sinai South Nassau in Oceanside, N.Y. “Droplets can go out the side. It’s a risk,” he says.

Dr. Glatt, who is also the hospital’s chief of infectious diseases, thinks they can help in a hospital setting. He doesn’t recommend wearing face shields in the community because he doesn’t feel it will reduce risk for the everyday wearer who is already wearing a mask. But he does think it makes sense to pair shields with masks for barbers, dentists and personal trainers who may require more protection.

When do face shields alone make the most sense?

Schools, especially with younger children, may benefit from offering face shields to students and teachers. Dr. Ostrosky says children liable to touch the masks or take them off need an alternative.

Face shields may also work best in settings like restaurants or coffee shops where employees must communicate with people. Masks “are a communication barrier in some settings,” Dr. McQuillen says.

Which materials and other specs are best?

Opt for shields with any kind of sturdy, clear, waterproof plastic and those that use foam to fill gaps at the forehead or attach securely to a hat or visor, Dr. Edmond says. “If the coughing person is on the taller side, the droplets may come over,” he says. The shield also needs to reach to the ears and just slightly below the chin, he says.

What’s the most effective way to clean and take off the shield?

Taking off personal protective equipment is key to preventing infection, Dr. Omer says. He recommends face-shield users disinfect their hands and slip off the shield without touching the clear plastic, especially the inside. Use a disinfectant spray, alcohol wipe or rinse with soap and water before putting it away in a place where it cannot get contaminated.

Some companies, including Midwest Prototyping, that already provide shields to hospitals are also starting to sell to consumers. Additionally, the University of Wisconsin- Madison offers open-source shield design for its Badger Shield, which is being used both in hospitals and nonmedical settings, says Lennon Rodgers, director of the university’s Grainger Engineering Design Innovation Lab.

What are the downsides to wearing a face shield?

With masks more popular, many are reluctant to switch or add additional face covering. “It’s awkward and puts a barrier between you and others. We’ve never done that,” says Dr. Ostrosky. “To a certain extent it’s a big behavioral and appearance change.”

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