How effective are antimicrobial “courtesy masks” at preventing the spread of contagious airborne illnesses?
The best evidence suggests that, when sick, wearing a mask can help to protect others from getting sick. And when well, wearing a mask around those who are sick will probably decrease your own chances of becoming infected. But the masks are far from foolproof.
Courtesy masks, or what we doctors refer to as surgical masks, were introduced into the operating room in the late 1800s. They quickly became popular among a public eager to protect itself against the influenza pandemic of 1918.
A century later, the advent of modern molecular techniques confirmed that surgical masks can indeed provide good protection against flu. In a 2013 study, researchers counted the number of virus particles in the air around patients with flu. They found that surgical masks decreased the exhalation of large viral droplets 25-fold. The masks were, however, less effective against the fine viral droplets that can remain suspended in the air longer and are therefore more infectious, cutting them by 2.8 times.
Surgical masks also afford fairly good protection for the worried well. In an oft-cited study of 446 nurses, researchers found surgical masks were as good, or nearly as good, at protecting the wearer against flu as respirators, a somewhat more high-tech, masklike device used in hospitals.
The work of Australian investigators provides further support for the value of the simple surgical mask. They estimate that in a home setting, wearing a surgical mask decreases a well person’s risk of getting sick by 60 percent to 80 percent.
Unfortunately, most people fail to wear a mask faithfully enough to achieve this degree of protection, and the Centers for Disease Control and Prevention remains equivocal about the use of masks outside of health care settings. “No recommendation can be made at this time for mask use in the community by asymptomatic persons, including those at high risk for complications, to prevent exposure to influenza viruses,” the agency concludes on its website.
If you don’t have a mask, or don’t want to wear one, standing at least six feet from an infected person will increase your chances for staying healthy. The air surrounding sick people, even if they aren’t coughing or sneezing, is loaded with small infectious aerosolized particles, and the farther you are from them, the better.
Washing your hands frequently, of course, is also critical for staying healthy, since touching infected fingers to the eyes, nose or mouth can transmit infection.
