The story of the United States’ evolving relationship with masks is a complicated one. When the pandemic started, Americans were told to save the masks for the healthcare workers. But before long, in April of 2020 that advice changed. The prevailing wisdom said to wear cloth masks, surgical masks or even N95 masks if we could find them, whenever we left our homes. If we couldn’t get a mask, we could wear bandanas over our nose and mouth. Anything to block viral particles from getting in or out of our noses and mouths, because scientists found that many individuals who were infected but didn’t have symptoms were spreading the disease.
At that point, many scientists believed that the virus was mostly spread via large droplets that quickly sank onto surfaces, rather than hanging around in the air. In May of 2021, the Centers for Disease Control (CDC) officially recognized that SARS-CoV-2 could linger in the air and spread via aerosolized transmission, which underscores the protective potential of covering your face. Still, the CDC generally recommended using whatever masks you could get your hands on, from a bandana to an N95.
Many months later, in January, the CDC updated its mask guidance again for the public. It highlighted that people “can choose” to wear the most protective masks against Covid-19: N95s or KN95s, though it didn’t specifically say not to wear the less protective surgical or cloth masks, even though they’re known to be less protective.
To find out what you should know about masks now, at this stage of the nearly two year-old pandemic, Smithsonian reached out to the experts to learn what works best and why.
What does a mask do? Who does it protect?
Masks are most effective at preventing the person wearing them from spreading the virus to others, explains Sandra Bliss Nelson, an infectious disease specialist at Mass General Hospital, but “as we have gotten towards more transmissible variants with a higher prevalence of airborne spread, protecting the wearer has taken more priority.”
The idea, of course, is that masks filter the virus out of the air before that air is breathed in, which is especially important if the pathogen is believed to be aerosolized. Much of the research behind masking in healthcare comes from decades ago when tuberculosis outbreaks were common, explains Lisa Brosseau, a retired public health scientist who consults for the University of Minnesota’s Center for Infectious Disease Research and Policy.
Additionally, face masks increase the humidity of the air that the wearer inhales. Richard Zare, a chemist at Stanford University, and his team have found that the increased moisture may play a role in decreasing the risk of exposure because water droplets start to produce the disinfectant hydrogen peroxide, which can neutralize the virus, when relative humidity climbs above 40 percent. In this increasingly muggy environment, the droplets that carry the virus collect water and grow larger, and “droplets of a certain size kill viruses and bacteria,” says Zare. “Masks do much more” than filter out the virus.
How effective are masks?
In April of 2020, a Covid-19 outbreak hit service members aboard the U.S.S. Theodore Roosevelt. Those crew members who self-reported wearing masks had 55.8 percent chance of being infected, whereas those who didn’t had about an 80 percent chance of getting Covid-19.
But one of the most convincing studies on the ability of masks to limit spread of Covid-19 was conducted on 600 villages in rural Bangladesh. For the study, published this past December in Science, entire villages were randomized to receive free cloth masks, surgical masks or no masks, along with education about and reminders to wear them (such as signs in public places). Overall, the study included 350,000 people. In villages where scientists promoted mask wearing, 42 percent of residents wore them in public, compared to only 13 percent in the other villages. Those villages with more masking had 9.5 percent fewer symptomatic Covid-19 cases than their bare-faced counterparts.
“That was the really the first powerful evidence that masks work” to prevent Covid-19, says Nelson.
The authors of the study emphasized that while a 9.5 percent difference may not sound like a lot, if more stringent controls, like mask mandates, caused more than 42 percent of people to mask up, the number of cases avoided might be much higher.
What is the difference between N95, surgical and cloth masks?
Not all masks are created equal. In fact, in the study of Bangladeshi villages, surgical masks were associated with an 11 percent drop in infections, whereas cloth masks only reduced infections by 5 percent.
All masks are designed to block viral particles from getting through, but some do so better than others. N95, KN95, KF94 and surgical masks are all made with cloths that have an electrostatic charge. This charge attracts the viral particles, so they get stuck in the fabric and don’t get through to your nose or mouth. The charge offers one more layer of protection that the strictly physical barrier of cloth masks doesn’t provide.
If properly fitted, an N95, KN95 or KF94 should filter 94-95 percent of viral particles. Despite quality filters, surgical masks are less effective because they aren’t designed to create a seal on your face, meaning the virus can easily slip through gaps.
Healthcare professionals are required to have a “fit test” to make sure their N95 masks are properly sealed and don’t leak, but for the rest of us, one of the easiest ways to tell, says Nelson, is “you can actually see the masks indent as you breath. That suggests you have a good fit.” She adds that “for individuals who wear glasses like I do, you can see if you’re glasses are fogging up. That means air is escaping out the top,” and your mask is not perfectly sealed.
In March 2021, Smithsonian ran an article about how to make your own masks. It recommended using 100 percent cotton flannel and inserting a filter (HEPA, if you have it, or a coffee filter) and research has shown that these masks can block droplets more effectively than bandanas or cloth masks with a single layer. Since there’s no longer a shortage of surgical or N95 masks, Brosseau says making your own masks is no longer “a good option, at all.”
How can you avoid counterfeits?
N95s, KN95s and KF94s are slightly different in terms of shape and style, but all use high-quality material that filters 94-95 percent of virus. Each type is regulated and certified in a different country. N95s are regulated by the United States’ National Institute for Occupational Safety & Health (NIOSH). The KN95 is designed to meet Chinese standards, and the KF94 adheres to Korean regulations. Unfortunately, no N95s are made specifically for children, but KN95s and KF94s do exist for kids. They still require the same level or approval as other masks.
Throughout the pandemic some manufacturers have added misleading words and logos to their labels to make the masks seem like they’ve been inspected and approved, even if they aren’t certified. NIOSH provides some examples of counterfeit masks here, and a list of approved N95s here. The FDA also has two lists of KN95 masks that were authorized for healthcare workers during the shortage of N95s.
You can also look at this infographic from the CDC that describes the information you should be able to find right on the front of any legitimate N95 mask. Similarly, you should see the name of the manufacturer, model and GB number on the front of a KN95 mask. The KF94s don’t have text on the front but should be made in Korea.
Another option is ordering vetted masks through the nonprofit website, Project N95, instead of suppliers like Amazon that may harbor counterfeits alongside certified masks.
How long can you wear masks and should you wash them?
If you’re a healthcare worker or someone who is regularly exposed to high levels of SARS-CoV-2, you might consider some of the strategies laid out in a New York Times article to reuse your masks. (For example, experts suggest with proper care a mask can be worn up to about 40 hours.) For the rest of us, Nelson says that most of the public isn’t exposed to that much virus. “So I tell people you wear it until it feels grungy, or it just feels like it's not really fitting very well anymore,” she says. But at that point, it’s time to just replace the mask, not wash it. “You can’t put them in the microwave. You can’t put them in water.”