federal judge in Florida struck down the U.S. Centers for Disease Control and Prevention (CDC)’s public transportation mask mandate on April 18, meaning that people no longer have to wear a mask on public transportation in most cases.
As mandates end, some public-health experts have advised people to keep masking on public transportation and in other crowded indoor areas, even if others around them aren’t. People at high risk for severe COVID-19—including those who are immunocompromised or have chronic conditions—may want to keep wearing a high-quality mask even when doing so isn’t recommended for everyone in their area, under CDC guidance.
But is “one-way masking”—or wearing a mask even if no one else around you does—really enough to protect you from getting infected by SARS-CoV-2, the virus that causes COVID-19?
“One-way masking is definitely better than nothing,” says Emily Sickbert-Bennett, director of infection prevention at UNC Medical Center—but she says it’s also not as good as universal masking.
A mask is meant to work in two different ways: by containing the wearer’s germs and filtering out other people’s germs. Masks can trap particles that are exhaled by two people. This will reduce germs in the air and lower chances of both getting sick. “One of the key things you want to do in infection control is block the source,” says Kimberly Prather, an aerosol expert and chair of atmospheric chemistry at the University of California, San Diego. “Never let it in the air in the first place.”
If one person is unmasked and freely exhaling germs, the burden of protection is all on the other person’s mask. Although cloth or surgical masks can provide some protection in such situations, respiratory protectors like N95s, KN95s, and KN95s filter almost all particles. They are the most effective and protective option for masking one way.
Published in the journal: A model study PNAS in December 2021 estimated a masked person’s likelihood of getting sick after talking with an unmasked person who has COVID-19. The researchers found that someone wearing a surgical face mask has a 95% chance of becoming infected in less than half an hour. This is even though they are seated approximately five feet from the person who needs it. However, someone with a respirator may have a 20 percent chance in the full hour. After an hour, infection risks dropped to 0.4% for both the person with the illness and their companion who wore respirators.
In other words, wearing a high-quality mask offers substantial protection even if others aren’t wearing one—but two-way masking is even better, the study suggests.
An insignificant CDC study, published February 2, provides real-world data. According to the study, people who reported wearing respirators at all times in indoor public settings were 83% less likely than those who did not. People wearing surgical masks had 66% less chance of getting COVID-19, while those who used cloth masks were only 56% more likely. Of course, someone who wears a respirator in public is likely more cautious about COVID-19 overall than someone who goes unmasked indoors—and the data are self-reported—but the CDC’s authors still concluded that masks help prevent people who wear them from getting sick.
Although N95s respirators are some of the best masks available, they can only be effective if they fit correctly. The respirator must fit snugly on the face without air leakage. This can be tested by placing your hands on your forehead and inhaling deeply. If your mask fits well, you shouldn’t feel any air escaping.)
You can also find many knockoff respirators on sale. Be careful. Real N95s are marked on their packaging with an approved label from National Institute for Occupational Safety and Health. Project N95, a non-profit organization that provides guidance and links to resources for authentic respirators in your area, also offers information on where you can find N95 masks free of charge.
If you don’t want to wear a respirator but still want to wear a mask in public, you can make a surgical mask more effective with a few simple adjustments, Sickbert-Bennett says. To make the mask fit more closely to your face, you can use the nose bar and ear loops to tighten it. Instead of pinching the nose, Sickbert-Bennett suggests that you smoothen the bars with both your hands. This can cause a leakage at your bridge. For extra protection, you can layer a surgical mask on top of a cloth mask.
Aside from staying up-to-date on COVID-19 vaccinations, “having a well-fitted mask is the best thing you can do” to protect yourself in public indoor settings, Sickbert-Bennett says. But it’s not foolproof. If you’re around someone with COVID-19, lots of factors can influence whether or not you get infected: how contagious they are, if they’re masked, how much protection you have from vaccines and prior exposures, how strong your immune system is, and so on.
Even though one-way masking isn’t perfect, Dr. Monica Gandhi, associate chief of the University of California, San Francisco’s division of HIV, infectious diseases, and global medicine, argues it’s an appropriate strategy now that highly effective vaccines and boosters are widely accessible in the U.S. and therapies are available for people who don’t respond well to vaccination.
Gandhi states that mask mandates are imperfect. Gandhi says that some people used masks incorrectly, or did not wear them at all. Others chose cloth masks of lower quality at first U.S. health officials urged. She argues it’s time to recognize those shortcomings, shift away from mandates, and instead encourage people who want extra protection to wear high-quality respirators.
The masks that are worn in indoor areas may not be available to everyone, so those most at risk could become more susceptible. Kids under 5 can’t get vaccinated yet, and older people and those who are immunocompromised may still be cautious about getting infected. “It’s a much bigger burden now on the high-risk individuals,” Prather says.
Prather believes that she would be more at ease about the U.S. ending its mask mandates if it had higher standards for indoor air quality measurement, ventilation and filtering of public indoor air. Cleaner indoor air could act as “a mask for the whole room,” reducing or even eliminating individuals’ need for actual masks, she says.
Until and unless that happens, though, wearing a high-quality mask in indoor spaces is a good way to help protect yourself—even if others aren’t.
Here are more must-read stories from TIME
