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A surgical mask and an N95 respirator. Officials in China are urging citizens to wear masks in public to stop the spread of the coronavirus. But can a mask really keep you from catching the virus?Science Photo Library/ Getty Images; South China Morning Post/Getty Images

As the Wuhan coronavirus continues to spread, officials in China are urging citizens to wear masks in public to stop the spread of the virus — and cities in China as well as other parts of Asia are reportedly running out of face masks.

But can a mask really keep you from catching the virus?

To answer that, it helps to clarify which kinds of masks we're talking about.

Because experts don't yet know exactly how the virus is transmitted, the Centers for Disease Control and Prevention is recommending that health care workers treat it like an airborne pathogen — germs that can travel in particles or droplets in the air. That means health care workers interacting with a coronavirus patient should wear a heavy-duty mask called an N95 respirator. These respirators are designed to fit tightly around the nose and mouth, and, when worn correctly, block out at least 95% of small airborne particles, according to the CDC.

But wearing an N95 respirator is serious business, says Dr. William Schaffner of Vanderbilt University Medical Center. Health care workers who use these respirators are required by law to undergo an annual fit test — a check to make sure the mask forms a tight seal on the wearer's face so that contaminated air can't leak in. Although N95s are disposable, workers must also demonstrate that they know how to put on and wear the model that they are using.

This type of mask is "difficult to wear" because it's uncomfortable, Schaffner says. Some people find it harder to breathe when wearing the N95. But "that's the kind of protection that really works."

While N95 respirators are available for the public to purchase, there's no recommendation from health agencies for the general public to wear them.

By contrast, surgical masks — those cheap, disposable, gauzy masks that often come in blue or green — are less uncomfortable. But Schaffner says the scientific evidence that "there might be a benefit for people in the community wearing [surgical] face masks is very, very meager. The general sense is perhaps, but they're certainly not an absolute protection." In other words, they do provide some benefit but they're far from foolproof.

Surgical masks are just a physical barrier that will protect you against "a visible splash or spray of fluid or large droplets," explains Raina MacIntyre, an infectious disease researcher and professor of global biosecurity at the University of New South Wales in Sydney who has studied the efficacy of face masks. These masks fit loosely on the face around the edges, so they don't completely keep out germs, and small airborne particles can still get through.

MacIntyre's research has shown that N95 respirators offer far superior protection. But in one study, she did find that family members who wore surgical masks when caring for a sick child at home had a lower risk of getting infected. But the benefit only occurred if people wore the masks "all the time when you are in the same room as the infected person," MacIntyre says — something many families in the study found difficult to do. "But if they did wear it, yes, they got protection."

MacIntyre notes that cloth masks — which people wash and reuse — are also common in Asian countries. She says there's no evidence to show they have any benefit, and her research suggests they "may actually be harmful," because infrequent washing and moisture retention can make cloth masks a breeding ground for pathogens.

Experts note that how you remove a mask — be it a surgical mask or an N95 respirator — is also important. If you touch the front when taking it off, you could end up contaminating yourself.

As for wearing a mask outdoors in public? Marybeth Sexton, an assistant professor of medicine in the division of infectious diseases at Emory University, says there's no need if you're in the U.S. or another country where the risk of catching the Wuhan coronavirus is considered low.

Sexton says wearing a surgical mask is a good idea if you have a respiratory illness and need to see the doctor. But that's really so you won't infect other people. Otherwise, she says, don't rush out and buy a mask. Leave them for the people who need them — like health care workers and ill people — so as not to contribute to mask shortages, she says.

Some infectious disease experts have also suggested that wearing a face mask may have some value if it keeps you from touching your face and nose. That's a common way germs get into our bodies — say, touching a doorknob someone sneezed on, then perhaps inadvertently bringing your fingers to your eyes, nose or mouth. But Clarence Tam, a public health researcher at the National University of Singapore, notes that because wearing masks can be uncomfortable, "the discomfort might make you actually touch your face more." This could contaminate your fingers with any germs that might have attached themselves to the outside of the mask.

Another potential downside? "If you see everyone around you wearing a mask, that also can be fairly alarming," Tam notes.

MacIntyre agrees there's no need to run out and buy face masks if you're in a low-risk country like the U.S. But she says the calculation may be different for people in a place like Wuhan, China, the epicenter of the coronavirus outbreak.

"If it's someone in Wuhan, where most of the cases have been, then there might be some value to it," MacIntyre says. "There's a lot of unknowns about this infection. That's the problem."

Observational studies found that wearing a surgical mask did provide health care workers some protection during the SARS epidemic. But MacIntyre notes that those studies were not randomized controlled trials, considered the gold standard in research. Tam adds that the health care workers who were responding to SARS were also using other protective measures.

And regardless of where you are, there is something that all the infectious disease experts I spoke with recommended everyone do to keep from getting sick: Wash your hands — frequently.

"Hand-washing for sure," Schaffner says. "Constantly. Frequently. All the time — summer, winter, whatever."

And get your flu shot. It is flu season, after all. It doesn't offer protection against Wuhan coronavirus, but here in the U.S., Sexton says, the flu remains the bigger risk to health.

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