Does wearing a face mask make you safer? What scientific studies tell us

While no face mask is 100 percent effective at reducing exposure to coronavirus, even a home-made mask will offer limited protection, scientists say. A mask worn by an asymptomatic or presymtomatic person who has been infected will protect others from the virus. less While no face mask is 100 percent effective at reducing exposure to coronavirus, even a home-made mask will offer limited protection, scientists say. A mask worn by an asymptomatic or presymtomatic person who ... more Photo: Tangmingtung@gmail.com/Getty Images Photo: Tangmingtung@gmail.com/Getty Images Image 1 of / 33 Caption Close Does wearing a face mask make you safer? 1 / 33 Back to Gallery

People around the world are increasingly donning face masks to slow the spread of the coronavirus pandemic. But the country with the most reported COVID-19 cases is the one that has repeatedly balked at recommending its citizens wear masks — the United States.

China has mandated that anyone going out in public in Beijing or Shanghai put on a face mask. South Korea, Hong Kong and Singapore, all with large segments of their populations wearing masks in public, have reported lower rates of infection than the U.S.

In Taiwan, the country that was best prepared for the pandemic and which had the foresight to stockpile masks, virtually everyone has worn a face mask in public since the outbreak was first reported in China. As of Tuesday, Taiwan had just over 300 confirmed cases, compared to the 190,000 in the U.S.

In Austria as of Monday, anyone entering a supermarket must cover their nose and mouth with a mask.

But does wearing a mask protect you from the novel coronavirus or does it just protect the people you come in contact with? Or does it have little effect at all?

The Trump administration has repeatedly warned against using masks and suggested they might even lead to more infections, not fewer. However, the Centers for Disease Control and Protection is now reconsidering its guidance against covering your face (unless you're sick).

The arguments against the public wearing masks include:

—“You can increase your risk of getting COVID-19 by wearing a mask, if you’re not a health worker — U.S. Surgeon General Jerome Adams to “Fox and Friends” last month.

—“If it's not fitted right you’re going to fumble with it.” — Health and Human Services Secretary Alex Azar in late February.

—Health workers need them (N95 respirator masks) more than the general public.

—They make you touch your face more — Dr. Anthony Fauci, an immunologist and the most respected member of the White House Coronavirus Task Force.

—Wearing masks gives people a false sense of security, inducing them to ignore social distancing or hand washing.

Certainly some of these arguments raise legitimate concerns. Supplies of N95 masks should go to health workers first. Masks can only do their job successfully if people adhere to other preventive measures, such as washing their hands regularly and maintaining 6-foot social distancing.

But if nothing else, wearing a mask — even a surgical mask or home-made mask — makes others safer, because it provides a layer of protection in the event that the wearer is infected. The evidence shows that SARS-CoV-2 is highly contagious and that some of those infected are asymptomatic or presymptomatic: They may feel perfectly healthy but can transmit the virus to others.

The 2013 study “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?” pitted homemade masks vs. commercial surgical masks. It found that both were effective in reducing the spread of microorganisms coughed out by the mask wearer — particularly in large droplets — although the surgical mask did a moderately better job.

“These masks would provide the wearers little protection from microorganisms from others persons who are infected with respiratory diseases,” the study’s authors wrote. Still, they concluded that any mask was better than no mask.

An earlier study suggested that both professional and home-made face masks do reduce the chance of exposure to respiratory infections.

The 2008 research by Marianne van der Sande, Peter Teunis and Rob Sabel in PubMed Central, the biomedical and life sciences journal, found that FFP2 (N95) masks provided adults with about 50 times as much protection as home-made masks and roughly 25 times as much as surgical masks.

“Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection,” the authors concluded.

There’s no guarantee that a mask will protect you with 100 percent effectiveness, but in other countries it seems to be helping when employed in concert with other preventive measures such as social distancing, frequent hand washing and disinfecting.

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Mike Moffitt is an SFGATE Digital Reporter. Email: moffitt@sfgate.com. Twitter: @Mike_at_SFGate