Medical Examiner

A Comprehensive Guide to Masks

Who needs them, what kind you should wear, when to wear them, and why.

A woman in profile wearing a face mask printed with seashells, with the Lincoln Memorial and reflecting pool in the background.
A woman wears a mask at the Lincoln Memorial on the National Mall. Olivier Douliery/Getty Images

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We’re going to be seeing a lot more face masks soon. After a week of rumors that the Centers for Disease Control and Prevention would advise regular folks to wear masks, President Donald Trump said in a press briefing Friday that “the CDC is advising the use of nonmedical cloth face covering as a voluntary health measure.”

This is awfully confusing. Back when this all started, we were told that we didn’t have to wear masks. You probably have some questions—about whether you should take the CDC up on the suggestion and about what changed. Here is our best shot at explaining what happened here!


So, what does the CDC say about masks now?


As of Friday afternoon, the recommendation in the CDC’s guide on how to protect yourself still has its old advice: no need to wear a mask unless you are sick. Trump indicated in the press briefing that the new guidance would only apply to people in coronavirus hot spots and noted that it was a mere recommendation, one that he himself would not be following. There will probably be updated guidance and clarifications in the days to come. For now, let’s go with: The CDC suggests you can wear a mask, if you want to, and you should wear a mask if you are sick.

This really sounds like I should just start wearing a face mask to be safe?


Not so fast. The answer currently is: It depends, both on the situation you’re in, and then, whom in particular you are asking. Like everything about this pandemic, the coronavirus is taking over the world as we are in the middle of learning about it, which means experts are making recommendations with less data than is ideal. “When you’re getting conflicting advice, it’s telling you that it’s really not a scientifically well-established point of view,” Robert Amler, a former CDC chief medical officer, now at New York Medical College, told me.


OK, so in what situations should I wear a mask?

There’s one situation in which the answer is a clear, obvious, scientifically agreed-upon yes: If you are sick, wear a mask.


The coronavirus definitely spreads through droplets from coughs; if you are coughing into a physical barrier, such as a surgical mask, it can stop those droplets, and even some of the smaller particles, from making it onto another person, or—more likely, since we are social distancing—onto a surface where another person might touch them and then touch their face. (This is why we are washing our hands so much.)

This is, in fact, why surgeons wear surgical masks—so “something dripping out of [the surgeon’s] face doesn’t drip into the wound they’re working on,” says Amler. They can also protect surgeons from getting splashed directly with bodily fluid. Surgical masks are not, medically speaking, meant to be worn by healthy people to stay healthy; they are just meant to block the exchange of liquids.


Of course, the tricky thing right now is figuring out who is sick, which is why delivering a directive like “wear a mask if you’re sick” does not quite cut it right now. Plenty of people don’t feel sick but still might be spewing around virus-filled droplets, hence, the current ongoing debate about whether we should just tell everyone to wear masks.


But I thought there was a mask shortage?

Yes, as you may have heard, health care workers working with COVID-19 patients—or potential COVID-19 patients—really, really need to be wearing heavy-duty masks called N95s. These masks are important because they’re strong enough to filter out particles, like viruses, rather than just blocking droplets. But there is currently a shortage of N95s. In response, the CDC has loosened their guidelines for health care workers to allow surgical masks as an “acceptable alternative.” Health care workers were upset about this, precisely because surgical masks do not work all that well to protect against direct exposure to someone with the virus. But it’s true that they are better than nothing: When researchers at the Health and Safety Laboratory in the U.K. sprayed aerosolized influenza particles at a test dummy from 2 feet away, they found that a well-fitted surgical masks didn’t eliminate exposure to the influenza to the extent that an N95 can, but they could reduce it tenfold. (That’s not a real-world scenario, exactly, but it’s also not that removed from what hospital workers experience.)


At any rate, among all the things we don’t know, at least the current hierarchy of masks is clear—N95 masks are most effective, then surgical masks, then homemade masks.


OK. So shouldn’t I let health care workers have the N95 masks, if there’s a shortage and all?

Yes, you really should. If you use an N95, a health care worker cannot use that N95. (If you have N95 masks that you would like to donate, the top entry in this Slate guide explains how you can do so.)

Even if we didn’t have a shortage, experts wouldn’t recommend regular people wear N95s. You have to be really careful to make sure an N95 fits properly, because air sneaking around the side makes them far less effective. You also have to dispose of them carefully after each use, so you don’t end up contaminating yourself via the used mask. And, an N95 “has its own side effects,” Amler explains. All that filtering slows down air flow, so they can also be a bit difficult to breathe through, so much so that the New York Department of Health has advised that clean-up workers who may need them for protection against chemicals check with their doctor if they have a preexisting condition. “It’s almost like breathing in a paper bag,” said Amler.


So I should wear a surgical mask?


If you have one in your possession already, yes, that’s probably your best bet. But surgical masks are out of stock or will take weeks to arrive from many retailers, plus hospitals need them, both so that sick patients can use them, and even so that health care workers who don’t have N95s can use them. So if you don’t have them, ordering them may not help.

… which leaves me the option of making a mask?

Yes. It’s not perfect—limited data suggest homemade masks are less effective than surgical masks—but it’s not nothing, either. There are a few studies that suggest that diligently wearing a mask when you have someone with a confirmed respiratory illness in your home can help reduce the spread. “Ideally, you want the sick person to wear a mask,” says Saskia Popescu, an infectious disease epidemiologist, in addition to having them stay as isolated as possible. But your own wearing of a mask will further limit the spread.

That masks are imperfect is just one of the reasons social distancing is still so important. Staying physically distant from one another keeps the possibility of spreading droplets between one another as low as it can be. The mask is just an additional thing on top, though it should help continue to lower the spread.

If you’re OK at sewing, you can download a pattern from the New York Times here. MarketWatch has instructions to make masks with a stapler or safety pins. And here’s how to make one with a handkerchief and hair ties.

Is there any downside to wearing a mask?

Actually, possibly. Many experts worry that masks will provide a false sense of security. “I worry that if people put on masks, then they’ll think, OK, I’m protected, and they won’t wash their hands as vigorously or be careful not to touch their faces,” Aaron Carroll, an Indiana University pediatrics professor said in an episode of Slate’s What Next. “Or worse, they’ll keep touching their faces because they keep adjusting the masks, or they might just start to be lax in their social distancing.”


There’s also the fact that a dirty mask can be a source of contamination. Masks are single use; they need to go in the trash or into a laundry bin. You need to wash your hands before you put one on and after you take one off. The World Health Organization has detailed instructions on proper mask etiquette here.

If you are careful not to let the mask lull you into a false sense of security, if you are able to wear it and not adjust it and touch your face, and if you follow best practices for taking it on and off—it doesn’t seem like it would hurt.


People who are in favor of masks argue that masks actually help keep all the other practices top of mind. In this theory, masks help remind you not to touch your face. They are a psychological signal that we are in a pandemic, as science writer Knvul Sheikh explained in the New York Times: “They serve as a visual reminder to improve hand hygiene and social distancing.” The studies showing they can reduce transmission within a household suggests that it’s possible this way of looking at it is true! Who’s right? Well, like everything about this pandemic, we need more detailed data to tell for sure.


OK, so if I’m sick, I should be wearing a mask to go outside.

No. If you’re sick, you should stay inside. Or, as Amler says: “If you’re going out even if you only have mild symptoms, we’re not going to get through this, and more people will die.”

Right. If I’m sick, I stay inside, and I can wear a mask inside to protect people who have to live with me.


 If I’m not sick, then I should still wear a mask?

You can, because you might still be spreading the virus. “We’re still learning a lot about the asymptomatic people,” says Popescu. For her, the evidence of asymptomatic transmission isn’t convincing enough to warrant universal mask-wearing. She thinks there might not be all that many truly asymptomatic people out there, just people ignoring mild symptoms. But it’s also possible that a lot of viral shedding happens when people are presymptomatic, as Caroline Chen points out in ProPublica, citing a small study of 94 patients that has not yet been peer-reviewed. One part of the solution to presymptomatic spreading is for everyone to “wear a mask, preferably universally in public spaces,” as Gabriel Leung, dean of medicine at the University of Hong Kong, told Chen.


So, everyone in Asia had this right the whole time?

Basically, yes.

But why has there been so much confusion over masks?

Part of it comes down to social norms: Mask-wearing is a norm in other countries—yes, including many that appear to have successfully flattened their curves. It’s unclear if mask-wearing actually helped to cause the flattening we’re seeing to a meaningful extent. But it does make sense that we’re looking at other countries, asking if what they did was helpful, and figuring out if we should be adjusting our own practices as a result.

In the end, the reason for the back-and-forth is the same reason that everything about this pandemic is confusing: We are learning a lot about it on the fly, scientifically. It’s unclear to what extent old standards apply. “I always go back to what we do during flu season,” says Popescu. In the U.S., we don’t wear masks during flu season. But influenza might spread less easily than the new coronavirus—it doesn’t spread through asymptomatic or presymptomatic transmission, for example.

Right now is also a lot different than flu season, in so many ways. Right now, almost everyone wants to do everything possible to stop the spread, to keep from getting sick. “In a state of fear, people want something to do to protect themselves,” says Popescu.  We have control over so little right now, as individuals, and masks are one thing that we can control.

For more on the impact of COVID-19, listen to The Gist.