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Some prefer face shields to cloth masks. Experts are split on effectiveness.

Health care workers use face shields to protect against coronavirus droplets. How well do they work for average people?
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A stylist wears a face shield and a mask at a salon in Arlington, Va., on May 29.Andrew Harrer / Bloomberg via Getty Images file

As new daily coronavirus cases in the U.S. keep spiking, government orders to require masks in public spaces are increasing, too.

The Centers for Disease Control and Prevention says cloth face coverings can help slow the spread of the virus that causes COVID-19, but many people still resist wearing masks.

Indeed, masks have become a flashpoint in the efforts to control the pandemic, with some people claiming they can't breathe well while wearing them.

But what about face shields? Face shields are worn like hats, with a curved piece of plastic that comes down in front of the entire face. Health care workers have long used them as protective equipment.

New York state counts face shields as an option to cover the face that can be used in lieu of masks, but experts are divided over how well they protect against coronavirus droplets.

"People who wear these homemade cloth masks are invariably touching their face constantly to adjust it, and we know that touching your face is one routine mechanism for infecting you," said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security. "When you're wearing a face shield, you're less likely to touch your face."

Face shields are also more comfortable for breathing and talking, Adalja said.

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"They don't impede your mouth, and you're talking and you're breathing as much. People subjectively feel very muffled when they're wearing a mask, and they feel less comfort when they're breathing when they're wearing a mask," he said.

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Dr. Eli Perencevich, an infectious disease physician and professor of internal medicine and epidemiology at the University of Iowa Carver College of Medicine, coauthored an opinion piece in the Journal of the American Medical Association about how face shields should be extended from clinical settings into communities.

Unlike masks, which help prevent users from spreading COVID-19, face shields also protect those wearing them from infection, Perencevich said.

He referred to a study that said face shields reduce inhalation exposure to influenza virus.

The study, published in 2014 in the Journal of Occupational and Environmental Hygiene, analyzed how well face shields block aerosol droplets. By using cough simulators, researchers found that face shields reduced exposure to inhaling cough droplets by 96 percent.

But the author of the study, William Lindsley, a research biomedical engineer at the National Institute for Occupational Safety and Health, said the general public should stick to cloth face coverings.

"A cloth mask or a medical mask is going to do a better job of protecting you against the smaller particles than a face shield would," Lindsley said. "A face shield is good against the really big stuff [particles] that you can kind of see. But as the stuff gets smaller and smaller, it's just easy for that to go around the face shield and be inhaled."

Even so, Perencevich said the study is reason to advocate for face masks.

"Masks are source control protecting others, whereas face shields are both source control and protecting yourself from the droplets landing anywhere on your face," he said in an interview.

Doctors, nurses and other health care workers in close contact with patients use face shields, along with N95 masks, to prevent virus droplets from getting into their eyes.

"We know that there's increasing evidence from all coronaviruses, but even this most recent SARS-CoV-2, if the virus lands in your eye, your conjunctiva, it can then kind of go through the tear ducts and kind of add to your system and get to your lungs and cause lung infection that way," Perencevich said.

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A meta-analysis published in The Lancet found that eye protection might significantly reduce virus infections in health care settings. But for the average person practicing social distancing, there's no real need to wear a face shield, said Dr. Bruce Polsky, an infectious disease specialist who is chairman of the department of medicine at NYU Winthrop Hospital.

Now that cheap face shields are sold at drug and convenience stores, some may wonder whether some models are more effective than others. Perencevich said a face shield's effectiveness depends on its design.

"Ones that go below the chin and back to the ears offer more protection than those that are more open," he said.

Despite their differing opinions on what is most effective, experts agree that covering your face is only one aspect of stemming transmission.

"It's like you're in a rowboat, and there's, like, four or five holes in the bottom of your rowboat," Lindsley said. "You can't just plug a couple of holes, because you're still going to sink. It all kind of works together."

Dr. Daniel Diekema, director of the division of infectious disease at the University of Iowa Carver College of Medicine, is another author of the JAMA article.

"All the types of face coverings are just one flawed prevention approach that shouldn't, you know, be a replacement for or lessen the importance of physical distancing, and perhaps most importantly, eliminating the close congregate indoor settings where we're seeing large numbers of infections take place," he said.