The debate over whether Americans should wear face masks to control coronavirus transmission has been settled.

Governments and businesses now require or at least recommend them in many public settings. But as parts of the country reopen, some doctors want you to consider another layer of personal protective equipment in your daily life: clear plastic face shields.

“I wear a face shield every time I enter a store or other building,” said Dr Eli Perencevich. “Sometimes I also wear a cloth mask if required by the store’s policy.”

Dr Perencevich is an infectious disease physician at the University of Iowa and the Iowa City Veterans Affairs Health Care System.

In an opinion article published last month in JAMA, he and two colleagues argued that simple, clear plastic face shields could help reduce the transmission of infections when added to public health measures like increased testing, contact tracing, social distancing and hand hygiene.

The idea is not just a thought experiment. In Singapore, pre-school students and their teachers will receive face shields when they return to school next month. Local health experts recommended teachers in Philadelphia wear shields when schools reopen, and a teachers union in Palo Alto, California, requested them as well.

But it can be difficult to imagine Americans being willing to put on another form of protective equipment. President Trump and Vice-President Mike Pence have shirked wearing masks in settings that would seem to call for them, and simple face covering requirements have provoked conflicts at grocery stores and restaurants.

Face shields have long been required equipment for many procedures in hospitals. Doctors and nurses wear them when intubating Covid-19 patients and during surgeries that may cause blood and bone fragments to fly out.

As debate arose over whether tiny coronavirus droplets could float on air currents, protecting the eyes and the entire face became a bigger issue in health care settings, said Dr Sherry Yu, a dermatology resident affiliated with Brigham and Women’s Hospital in Boston. People needed them to do nasal swabs for the coronavirus test or for triage in the emergency room. As shortages loomed, Dr Yu was among the many people and groups around the country who began fabricating face shields for front-line health care workers.

“The nice thing about face shields is that they can be resterilised and cleaned by the user, so they’re reusable indefinitely until some component breaks or cracks,” Dr Yu said. A simple alcohol wipe or rinse with soap and hot water is all it takes for the shields to be contaminant-free again.

Surgical masks and N95s, on the other hand, are meant to be disposed after each use, although some studies have shown masks can be reused two or three times after being sterilised before they lose integrity.

Dr Perencevich believes that face shields should be the preferred personal protective equipment of everyone for the same reason health care workers use them. They protect the entire face, including the eyes, and prevent people from touching their faces or inadvertently exposing themselves to the coronavirus.

Face shields may be easier to wear than masks, he said, comparing them with wearing glasses or a hat. They wrap around a small portion of a person’s forehead rather than covering more than half their face with material that can create the urge to itch.

Many people also wear masks incorrectly, letting them dangle off the tips of their noses, or concealing just their mouths. People also tend to re-adjust face masks frequently, or remove them to communicate with others, which increases their risk of being exposed or infecting others, he said. And while cloth masks can prevent people from spreading germs to others, they don’t usually protect the wearer from infection.

Face shields can also aid people who depend on lip-reading, Dr Perencevich said. They may be slightly dorky-looking, but the shields allow facial expressions and lip movements to remain visible, while serving as an obvious reminder to maintain social distancing.

Still, he and other experts acknowledge that face shields have their limits.

Just like masks, they must be removed when eating in cafeterias or restaurants.

And studies on how effectively they can reduce a person’s viral exposure are scarce.

One cough simulation study in 2014 suggested that a shield could reduce a user’s viral exposure by 96 per cent when worn within 18 inches of someone who was coughing. But most people in the general public are much farther away from others they are interacting with, said William Lindsley, a bioengineer at the National Institute for Occupational Safety and Health who led the study.

Large droplets that may contain virus will fall to the ground quickly, reducing the need for a face shield worn when standing farther away.

Even in close range, there can be scenarios where face shields are not as effective as masks like N95s that create a seal around one’s face.

“If you’re facing sideways, or I’m behind you, maybe you’re sitting at a desk and I’m standing, there’s other scenarios you can imagine where droplets can come around a face shield,” Dr Lindsley said.

There is also no research on how well one person’s face shield protects other people from viral transmission, the concept called source control that is a primary benefit of surgical and cloth masks.

One of the main reasons the Centers for Disease Control and Prevention changed their recommendations to suggest everyone wear a face covering in public was to protect others in case they were among the asymptomatic or pre-symptomatic group of people infected with the virus.

“I’m a huge fan of face shields,” said Saskia Popescu, a senior infection-prevention specialist at George Mason University in Fairfax, Virginia.

“But I don’t think we can swap them out for face masks just yet.”

Dr Perencevich and his colleagues expect that more research will show shields to be superior to cloth masks, not only because shields provide full face protection but as they are nearly impossible to wear incorrectly.

“Remember, effectiveness depends not only on the inherent properties of the facial covering but also how well the facial covering is worn,” he said.

And he and his co-authors like to imagine that people who are reluctant to wear masks will find face shields more comfortable: Once a person tries one on, they say, the wearer realises its many benefits.

Public health experts have reacted in horror both at the sight of public places where people have crowded without masks, and at demonstrations, like those in Michigan and California, where protesters without masks have been jammed together and at times yelled in the faces of police officers. Experts described wearing a face covering as a considerate act meant more to protect others than the person wearing it.

Dr Deborah Birx, the White House coordinator for the coronavirus task force, said she was alarmed at the sight of protesters huddled together without masks, such as those at the Michigan State Capitol.

“It’s devastatingly worrisome to me personally,” Dr Birx said on Fox News Sunday, “because if they go home and infect their grandmother or their grandfather who has a co-morbid condition, and they have a serious or unfortunate outcome, they will feel guilty for the rest of our lives”.

“We need to protect each other,” she went on, “at the same time we’re voicing our discontent.”

Even as governors imposed orders and public health experts dispensed their professional guidance, the effort to thwart the coronavirus nevertheless amounted to a grand national experiment in cooperation that hinged on the individual decisions of millions.

Governor Mike DeWine of Ohio had included a face-covering mandate as part of plans to reopen businesses, but he changed course.

“It became clear to me that that was just a bridge too far,” DeWine, a Republican, said Sunday on ABC’s This Week.

“People were not going to accept the government telling them what to do.”

As many states have moved towards reopening but have also set their own pace in doing so, an elaborate patchwork of orders and restrictions has emerged that differs from state to state, even municipality to municipality.

New York Times News Service