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What Experts Know About Masks and COVID-19

The CDC recommends wearing a fabric mask in public where social distancing is difficult, like at the grocery store

A person holds a sewn handmade fabric mask. ( Rike_ / Getty Images)
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The Centers for Disease Control and Prevention (CDC) now recommends wearing cloth face masks in public settings where social distancing measures are difficult to maintain, the agency announced Friday evening. The guidance is considered a voluntary precaution to be used in addition to social distancing and proper hand-washing.

Taking into account recent evidence that people can still spread the virus if they are not showing symptoms, the CDC reversed their initial advisory that surgical masks and N-95 respirators be reserved for healthcare workers and other medical first responders.

On the agency’s website, they suggest fashioning “homemade cloth face coverings” out of old T-shirts or bandanas. Even before the recent CDC recommendation, fashion designers pivoted to making fabric masks and do-it-yourself tutorials spread on social media. But what can—and can’t—masks do to prevent the spread of COVID-19?

Why Do Masks Help Prevent the Spread of ­COVID-19?

COVID-19 is caused by a novel type of coronavirus called SARS-CoV-2, a tiny particle of genetic material wrapped a fatty coating covered in spiked proteins that give it a crown-like appearance. The virus travels from person to person through droplets that are expelled when someone coughs, sneezes, talks or exhales.

As Roxanne Khamsi reported for Wired in mid-March, these droplets are big enough that they fall out of the air faster than the water in them evaporates, but research has shown that they can travel up to 26 feet before hitting a surface. A person’s mouth and nose are quick entry points to the body’s interior where an infection can take hold. So if the drops land directly on someone’s face, or if the drops land on a surface someone touched with their hand and then they touch their face, there’s a good chance of getting infected.

Ideally, fabric masks, bandanas and scarves will act as a physical barrier that could keep droplets off a person’s face, or keep an infected person’s virus-carrying droplets to themselves.

When experts say that SARS-CoV-2 is not airborne, they mean that it doesn’t travel in aerosols, which are what’s left behind if the droplet’s water evaporates and leaves behind a floating, dried-up germ in the air. (For example, tuberculosis travels this way.) But details of how COVID-19 spreads in droplets are still unclear, like how much of the virus is needed to cause an infection, how far it travels in the air when indoors versus outdoors, or whether far-traveling drops of the virus are affecting the pandemic’s course.

To get specific answers, “you’d have to expose animals to different quantities of airborne viruses, see if they get infected, and relate that to measures of the virus [in places] where people are infected,” Harvard epidemiologist Bill Hanage tells the Atlantic’s Ed Yong. “This is the type of stuff people will work on for years, but no one is going to find out for the moment.”

Why Medical-Grade Masks Are Reserved for Healthcare Workers

Depending on what they’re made of, different masks offer varying levels of protection. N95 respirators are some of the most powerful tools healthcare providers can use to protect themselves from the virus. But right now, we are facing a nationwide shortage of these important shields, according to the CDC.

When worn properly, N95 masks cover the mouth and nose, pressing closely against the wearer’s cheeks, so that any time the wearer inhales, the air is pulled through the mask. The mask is made so that at least 95 percent of small particles, including viruses like SARS-CoV-2, get trapped in its material, filtering clean air for the wearer to breathe.

To ensure N95 masks fits properly, healthcare workers have to get their personal masks fit-tested by professionals. Without this fitting process, the masks cannot reach their 95 percent filtration success rate.

For National Geographic, nurse Rosem Morton describes the process of getting fitted for an N95 mask:

I assumed the fit testing, as the process is called, would consist of teaching us how to wear the masks properly. It was so much more than that. Over the N95 masks, we are asked to wear a large white hood. To test the seal of the mask, a supervisor sprays a test substance through a hole in the hood and checks if we detect a bitter taste. We move our heads side to side and up and down. We read a lengthy paragraph. We walk around. It took me a couple of tries to perfect the seal.

I think about the public, the people who bought their own N95s and never had access to a fitting. They are under the false assumption that they are protected. A small mistake in sealing the mask could be fatal.

Right now, N95s are being reserved for healthcare workers who are most at risk of COVID-19 exposure, like those who collect the nose and throat swabs for tests, per Buzzfeed’s Zahra Hirji.

The other medical masks in use are surgical masks, which sit more loosely on the wearer’s face. The openings around the mask mean that they don’t completely filter the air like an N95 respirator, but they can still reduce the wearer’s chances of spreading or contracting disease. Pleated surgical masks have three liquid-resistant layers. The middle layer is made of melt-blown fabric, a difficult-to-manufacture mesh made of micron-wide polyester designed to catch infectious particles.

Research published last week in Nature Medicine shows that, in experiments conducted between 2013 and 2016, surgical masks worn correctly significantly reduced the spread of respiratory viruses from sick patients sitting in hospital exam rooms, based on measurements of both droplets and genetic material in aerosols.

Medical-grade masks are supposed to be thrown out after one use, but because of the medical mask shortage, healthcare workers are reusing their masks between patients to preserve their supply.

How Do You Make Your Own Mask?

For everyone else, fabric masks should work well enough as long as people also follow social distance measures and conduct thorough hand washing. It is still important to make sure medical-grade masks are available to healthcare workers who are exposed to the virus every day, reports PBS Newshour’s William Brangham.

“The last thing that we would want is for individuals to buy masks, hoard masks, and really make it even more challenging for our health care workers, who are going to be infected themselves, and then infect other people as a result,” emergency physician Leana Wen tells PBS Newshour. Wen argues that it is not time for the general public to take up widespread mask use.

Wearing an N95 to go grocery shopping would be like watering the garden with a firehose, causing more harm than good by taking necessary equipment from emergency personnel.

“The potential for exposure is so much lower in a grocery store compared to working in a hospital close to patients,” virologist Linsey Marr tells the New York Times’ Tara Parker-Pope.

Fashion designers are sending cloth masks to hospitals to be used as a last resort in high-risk situations. The handmade craft website Etsy has also started to encourage its vendors to sew and offer cloth masks.

Cloth masks aren’t made with melt-blown fabric or regulated by the FDA like medical masks. But an experiment conducted in 2013 by public health officials in England showed that a cotton T-shirt filtered about 50 percent of viral particles from the air and a tea towel filtered 72 percent compared to a surgical mask’s 89 percent filtration rate.

Masks also contain a wearer’s respiratory droplets to help prevent the spread of infection. New research shows that up to a quarter of SARS-CoV-2 carriers show no symptoms of COVID-19, and infected individuals could be contagious up to two days before they begin to show symptoms.

“I’ve been slightly dismissive of masks, but I was looking at them in the wrong way,” Hanage tells the Atlantic. “You’re not wearing them to stop yourself getting infected, but to stop someone else getting infected.”

The CDC now has its own mask-making tutorials, including no-sew designs and sewing templates. One method just requires cutting up an old T-shirt and another uses a coffee filter, bandana and rubber bands. An epidemiologist-designed pattern suggests adding a pipe-cleaner or wire so that it fits snuggly to your face. One tutorial published by The Oregonian, suggests using a reusable grocery bag made of non-woven polypropylene, which is similar to the material in N-95 masks.

If you choose to wear a mask, avoid temptation to adjust it frequently and be sure to remove it by the ear straps and not the part that covers your mouth so you don’t contaminate your hands. (Think of it as a reminder not to touch your face.) And be sure to wash it often.

“There are a lot of questions about what mask do you need in what situation, and how much protection do they confer? The idea is that some barrier is better than nothing.” Yale University cardiologist Harlan Krumholz tells PBS Newshour. “Do you need evidence beyond a shadow of a doubt that it's effective before people start wearing them? Or do we say that, in this moment of time, it's prudent to do so? And I favor the idea that we should.”

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