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This is a video made by a group of German physicists.
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The circle in the background is a kind of mirror,
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that, combined with a special photography technique,
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allows you to see the flow of air.
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In this case, it is showing how far air particles travel when someone breathes.
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And when they cough — which makes the respiratory particles travel further, and faster.
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This is what it looks like when someone coughs into their hand.
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And into their elbow.
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And this shows the travel of air particles when coughing while wearing two types of masks:
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a dust mask, and a surgical mask.
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This isn't a scientific study. It simply shows something face masks do very well:
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They limit how far away from you respiratory particles can travel.
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But whether you've been told to wear a face mask to prevent the spread of Covid-19,
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probably depends on where you live.
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In some East Asian countries, it's already common practice.
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Some European countries have also started mandating face masks in public spaces.
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But in the US, the message from the federal government has been inconsistent.
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“There's no reason to be walking around with a mask...
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it's not providing the perfect protection that people think that it is.”
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“The CDC recommends wearing cloth face coverings in public settings
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where other social distancing measures are difficult to maintain."
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“This is voluntary. I don't think I'm going to be doing it.”
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Unless you live somewhere that mandates it, whether you wear a face mask is probably up to you.
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But making that decision for yourself is a lot easier
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if you understand what face masks can actually do.
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And what they can't.
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Here's where the experts agree: If you are sick, and you leave the house,
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you should wear a face mask, because it keeps your germs in.
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Most of the uncertainty around masks is related to a separate question:
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whether healthy people should wear them too.
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Right away, though, that distinction, between sick with covid-19, and healthy,
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is more complicated than it sounds.
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People who catch covid-19 don't feel symptoms for 5-6 days on average,
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and even up to 14 days,
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but are contagious before that.
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And based on what we know right now, about 25% of people who catch it never show symptoms at all,
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but are also contagious.
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In other words, especially with covid-19,
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feeling healthy doesn't necessarily mean you don't have it.
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"I think we should all be acting, and also all assume, that we're infected."
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Shan Soe-Lin is an expert on global public health,
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and Robert Hecht is a professor of clinical epidemiology.
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And they say the possibility of being asymptomatic is one of the best cases for universal mask wearing.
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"Those who are actually infected and don't know it, or showing almost no symptoms,
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it's not even primarily for their own health.
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It's for the health of their family and neighbors."
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But let's say you definitely, 100%, do not have the virus.
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The first thing you need to know is that no mask can actually guarantee that you won't get it.
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Instead, the best way to think about face masks is as part of a larger set of protective measures,
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along with social distancing and hand-washing.
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Used together, they don't protect you completely,
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but they dramatically lower your odds of infection.
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"I think of it as a protective triad, with the virus trying to get in.
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And if you don't have one of the branches in it,
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then you're not protecting the whole thing.
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And if you didn't have a mask, could you do better with social distancing and hand-washing? Sure.
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But having all three is really, really important."
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To understand how that works, let's look at the two ways covid-19 is transmitted.
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One way is by touching an infected surface and then touching your face.
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This is called fomite transmission.
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And frequent hand-washing is the best defense against this.
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But wearing face masks correctly can play a role too:
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"Masks do a really good job of keeping you from touching your face."
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The second way someone's respiratory particles can reach you is directly. Like this:
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This is a slowed-down recording of a sneeze.
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It shows the kinds of respiratory particles a sneeze emits,
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and how far they travel.
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From a sick person, these droplets are packed with millions of viral particles
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that fall in close range, and infect whatever they land on.
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Social distancing protects us from droplets, by keeping you away from the particles emitted
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through sneezing, coughing, or even talking.
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But face masks could help there, too:
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"If someone sneezes a couple of feet away from you, it'll protect some of the bigger splashes."
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That also means face masks are especially important
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for people who don't have the privilege of being able to social distance:
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"That would be cops. That would be grocery clerks."
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"Taxis, Uber, FedEx, UPS..."
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"Anyone who's coming into contact with a lot of people,
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and maybe can't always maintain that six-foot distance."
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Look at this video again, though,
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and you'll see that we also produce these longer-range, smaller particles,
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which evaporate, and can leave the virus hanging in the air.
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These are called aerosols.
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And we still don't really know how infectious they are for the average person.
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But experts think they mostly pose a threat to medical workers,
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who work up close to patients with Covid-19.
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"If you're a foot away from the patient, who's coughing as you're trying to intubate them,
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aerosols are going everywhere.
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For you and me, just walking around, walking your dog, going to a grocery store,
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your risk is way higher from fomites."
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A common mask that protects against aerosols is called an N95 respirator.
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Its name comes from its material's ability to filter out 95% of aerosol particles.
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It's also fitted to form a seal around your mouth and nose, so there's no leakage.
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In lots of places, N95s are in short supply, because of diminished government stockpiles
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and disruptions in the supply chains.
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And that's true for all disposable masks, not just N95s.
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That's why the US Center for Disease Control says that unless you're a health care worker,
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you shouldn't be using either N95s or regular surgical masks.
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They're needed in hospitals, and the level of protection most people need can come from
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a simple cloth mask.
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The CDC recommends any kind of tightly woven cotton for the mask, or even a T-shirt.
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You can make them by consulting the countless internet tutorials out there,
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or buy them from the many vendors who manufacture them.
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But they only work if you wear them correctly.
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"So what kind of masks are you wearing? Do you have them handy? Could you show us?"
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"We thought you might ask."
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"This is all it takes to put it on:
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Just grab it by the loops. Keep your hands off the central part.
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Put it over your nose and mouth. Loop it around the ears.
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Be careful not to touch it when you're outside. Keep your hands away from your face.
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When you come back in, after walking the dog,
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or doing the groceries, do the same thing in reverse.
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Put it off to the side. Don't start playing with it.
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And then at the end of the day, pop it in the washer."
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"You wash it every day?"
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"I wash them every night. And, you know, if you don't have a washer,
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you can hand wash them every night. They're very small and they'll be dry by the next morning.
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So if people can have a couple, it would be better.
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But if you only have one, then just wash it at night."
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Face masks highlight something important in the fight against covid-19:
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That it isn't always about protecting yourself.
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It's about protecting the people around you.
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And if everyone is doing it, we all protect each other.
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"There's a visual messaging that comes from wearing a mask:
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A reminder to everybody, that we're not in normal times now.
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Everyone needs to be doing everything they can to protect themselves, and other people."