Editor's note: This story was updated March 31 to include that the CDC is considering the recommendation that the general public wear face coverings in public. Also, that there is circumstantial evidence that the virus spreads through a fine mist known as aerosol.

The public doesn't need to wear heavy-duty respirators, but it's a smart idea to don a face mask or wrap a clean scarf around your nose and mouth if you're going into a crowded place during the COVID-19 outbreak, an infectious disease doctor told Live Science.

The Centers for Disease Control and Prevention (CDC) may soon agree with this assessment; the agency currently states that healthy people do not need to wear face masks unless they are caring for someone who is ill with the new coronavirus. But an anonymous federal official said that the CDC may change these guidelines, in effect encouraging people to cover their faces in public, The Washington Post reported on March 30.

That said, the public does not need to wear face masks most of the time, said Dr. Otto Yang, a professor in the Department of Medicine and the Department of Microbiology, Immunology and Molecular Genetics at the David Geffen School of Medicine at the University of California, Los Angeles.

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If you're out for a walk — in essence, going to a setting where you can be at least 6 feet (1.8 meters) from other people, "then I think that not having a mask is fine and that fits the CDC recommendations," Yang said.

But, in his opinion, "If you have to be in a crowded situation, perhaps on a plane or waiting in line at the airport, it might make sense to wear a mask," Yang told Live Science.

The discussion about face masks has become a national conversation. Many people in the public are buying face masks to protect themselves. But health care experts have urged against hoarding, since these supplies are desperately needed in hospitals. Even the U.S. surgeon general tweeted "Seriously people — STOP BUYING MASKS!"

"The CDC, it's like they're talking out of both sides of their mouth," Yang said. "One side of their mouth is telling the general public, 'Hey, you don't need masks, forget about it.' The other side is, 'Health care workers need to wear N95 respirators.'"

"Is that a double standard?" Yang said. "Are they valuing some people more than others?"

Droplets or aerosol

Some of the confusion about "masks versus N95 respirators" exists because so little is known about COVID-19. At first, it wasn't clear if the virus spread predominantly through large respiratory droplets (like influenza) or also through a fine mist, called an aerosol, which can linger for hours (like measles). This great unknown made it unclear whether a heavy-duty mask, known as an N95 respirator, which blocks the smallest virus particles, or a regular surgical mask, which only blocks larger droplets, was better suited to protect against the virus.

At first, the CDC advised health care workers to wear N95 respirators because it wasn't clear whether COVID-19 could spread through aerosol. A March 17 study in the New England Journal of Medicine (NEJM) seemed to justify the fear of airborne spread, showing that the new coronavirus SARS-CoV-2 could survive in the air for up to 3 hours as an aerosol.

But Yang doesn't see it that way. The new study showed that the virus was viable as an aerosol in a lab, but not in real life, he said. In the study, the researchers "took extremely concentrated virus, much more concentrated than a person makes, they used an artificial aerosol machine [a nebulizer], which probably generates way more aerosol than a normal person does," Yang said. "So their conclusions were in this system."

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The researchers of that study looked at SARS-CoV-1 (the original SARS from the 2003 outbreak) and SARS-CoV-2 and found that both could be aerosols. "But we already know that the original SARS virus was not transmitted that way," in the general public, so that makes their model "not very believable," Yang said.

In other words, except in certain hospital situations such as a bronchoscopy, which essentially creates a fine mist of virus, SARS-CoV-2 is likely spread mostly through droplets, like the flu, Yang said. That's supported by a Feb. 24 case report in the Canadian Medical Association Journal, which found a man sick with COVID-19 on a flight from China to Canada in January did not infect his fellow passengers, even though he had a dry cough during the 15-hour flight. The man was wearing a face mask, but because no one else on the plane got infected, this case "supports droplet transmission, not airborne, as the likely route of spread of the COVID-19," the researchers of the case study found.

However, it's still unclear whether the virus can spread through aerosol. For example, after the Skagit Valley Chorale in Washington met for rehearsal on March 6, 45 of its members were diagnosed or showed symptoms of COVID-19, at least three were hospitalized and two were dead within three weeks, according to the Los Angeles Times. Perhaps the choir singers' forceful breathing as they sang dispersed the viral particles, Jamie Lloyd-Smith, an infectious disease researcher at the University of California, Los Angeles and a co-researcher on the NEJM study, told the Los Angeles Times.

"One could imagine that really trying to project your voice would also project more droplets and aerosols, Lloyd-Smith said.

N95 respirator or face mask?

Due to the N95 respirator shortage, the CDC recently relaxed its guidelines, saying that among health care workers, face masks were "an acceptable alternative when the supply chain of respirators cannot meet the demand," except in situations when respiratory aerosols might be produced, such as intubation or nebulizer treatments.

In addition to the shortage, N95 respirators are challenging to put on. Doctors receive annual training on how to mold the respirator around the face. As a test, doctors put on a hood and have the artificial sweetener saccharin sprayed in. "If you're wearing the mask properly, you don't taste any saccharin," Yang said. But most people do, he noted.

For this reason, the N95 respirator isn't recommended for the public, since it requires training to put on properly. Moreover, the N95 respirator is thick, so it's hard to breathe through.

In a nutshell, the public does not need N95 respirators; they likely will not be in a situation where they're exposed to aerosol of the virus, and these masks are needed by health care workers who will, Yang said.

"There's no reason for the general public to wear N95's," Yang said.

However, even regular face masks are in short supply, prompting the CDC to recommend the use of bandannas and scarves when necessary. There's not a lot of research on homemade masks, but a small 2013 study found that masks made from cotton T-shirts were effective, though not as good as surgical masks.

"The surgical mask was three times more effective in blocking transmission [of microorganisms] than the homemade mask," the researchers of that study found, who noted that homemade masks "should only be considered as a last resort to prevent droplet transmission from infected individuals."

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For people opting to use scarves and homemade masks, Yang recommended washing them after every use, and to stop wearing them when damp from breathing. Wearing eye protection, such as a face shield or goggles, could also physically block the virus, said Yang and Dr. James Cherry, a professor of pediatric infectious diseases at the David Geffen School of Medicine, University of California at Los Angeles.

In a 1987 study Cherry did with colleagues, health care workers who wore face masks or goggles were less likely to get respiratory syncytial virus (RSV) from hospitalized children than doctors who did not take these measures.

However, unlike Yang, Cherry agreed with the current CDC guidelines, and said that except for certain exceptions, the public doesn't need to wear face masks, as did Dr. Jaimie Meyer, an infectious disease specialist at Yale Medicine. That's especially true given that the safest way to avoid being exposed, or exposing others, is to simply stay home.

"The current CDC guidance says the general public does not need to be wearing surgical masks," Meyer told Live Science. "The best protection is to focus on social distancing, hand-washing, not touching their faces and bleaching high touch surfaces."

Originally published on Live Science.