Do I need to wear a face mask to block coronavirus?

Algerian women wore protective masks. The coronavirus is spreading around the world - and people are trying to block out the germs.RYAD KRAMDI/AFP via Getty Images

With concern about coronavirus coming to the United States on the rise, many people may be wondering if they should rush out to buy a face mask to filter out the pernicious germs.

But unless you’re sick or taking care of someone who is sick, you don’t need to wear one, experts say.

The state Department of Public Health says on its website that “at this time we are not recommending that people wear masks when they are in public. Masks can be useful in some settings, such as a clinic waiting room, to prevent someone who has a respiratory illness from spreading it to others. There is no hard evidence that wearing a mask protects the wearer outside of the healthcare setting.”

“CDC does not recommend that people who are well wear a face mask to protect themselves from respiratory diseases," the US Centers for Disease Control and Prevention says on its website.

“Face masks should be used by people who show symptoms of COVID-19 to help prevent the spread of the disease to others," the CDC says. "The use of face masks is also crucial for health workers and people who are taking care of someone in close settings (at home or in a health care facility).”

If you’re coughing and sneezing, wear a mask. But if you’re healthy, you only need to wear a mask if you’re taking care of someone, the World Health Organization says succinctly on its website.

The WHO also emphasizes that masks are “effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water" and if you wear a mask, then you must know how to use it and dispose of it properly.

“The main point of the mask is to keep someone who is infected with the virus from spreading it to others,” Timothy Brewer, a professor of epidemiology and medicine at UCLA’s Fielding School of Public Health and David Geffen School of Medicine, told The Washington Post.

Common surgical masks block the droplets coming out of a sick person from getting into the air, but they are not tight enough to prevent what’s already in the air from getting in, the Post reported.

Dr. Yonatan Grad, a professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health, said in an e-mail, “It’s unlikely that surgical masks will be of much benefit in efforts to prevent becoming infected with coronavirus. First, the material isn’t made to filter viruses. Second, people are likely not used to wearing masks, and so will be more likely to touch their faces and will do so more frequently, thus actually increasing the risk of getting the infection. What people should be trying to do instead is practice washing their hands regularly, greeting others without shaking hands, and not touching their faces.”

There are specialized masks — known as N95 masks because they filter out 95 percent of airborne particles — that are more effective, and some online retailers are sold out of them. But there’s a problem: The masks are difficult without training. They also must be fitted and tested to work properly.

“If you just buy them at CVS, you’re not going to do all that,” Brewer said. “You’re not going to get it fit-tested, and you’re not going to be wearing it properly, so all you’ve done is spend a lot of money on a very fancy face mask.”

The N95 masks are “used in healthcare settings to help protect healthcare workers, but healthcare workers undergo annual testing to make sure they’re properly fit. I advise against N95s for public use, because they won’t necessarily have the proper fit and because it’ll be important for N95s to be available to healthcare workers. Again, I think it would be better to become familiar with how to protect yourself through social distancing and good hygiene,” Grad wrote.

Material from Globe wire services was used in this report.