Julian Montague

Editor’s Note: Every Wednesday, James Hamblin takes questions from readers about health-related curiosities, concerns, and obsessions. Have one? Email him at paging.dr.hamblin@theatlantic.com.


Dr. Hamblin,

We have been told that washing our hands with soap and water for 20 seconds kills the virus, and that the virus doesn’t stay viable on surfaces for more than a couple of days. So why are we told that masks need to be washed with hot water? Isn’t simply not using a mask for several days before wearing it again sufficient for any virus to expire before reuse? These recommendations don’t seem to rationally fit together.

Linda Wieland

Ottawa, Canada


There is no such thing as a perfect mask. Every type involves trade-offs. A loosely wrapped bandanna may be barely better than nothing. N-95s dig into your face and bruise you. Gas masks are clunky and scare your neighbors.

Surgical masks come closest to perfect for this moment. They are feather-light, breathable, and electrostatically charged to catch viruses without blocking air. They seal tightly around your face, but not so tightly that they cause injuries when worn all day. In an ideal world—one where we didn’t have to worry about supply chains, waste, or cost—surgical masks would fall from the sky each morning and evaporate each evening. Wearing homemade face coverings, let alone having to wash them, would be an alien concept, as absurd as fashioning one’s own pacemaker from household items.

But as 2020 has made emphatically clear, this is not an ideal world. Even inside hospitals in the United States, which spends twice as much as the average country in the Organization for Economic Development on health care, doctors and nurses who typically discard masks after a single use have been instructed by the FDA to take the risky step of rationing and reusing them. New guidelines are being invented for this moment, and they don’t necessarily make sense. A public information page maintained by Johns Hopkins University advises that surgical masks should be thrown away when they are “visibly soiled or damaged.” Of course, having dirt or syrup on your mask doesn’t necessarily mean it’s nonfunctional. Meanwhile, masks that look perfectly fine could harbor the virus.

In normal times, the use of homemade masks is actively discouraged, because they can be contaminated, they encourage touching your face, and they don’t clearly protect people unless they are made well and worn assiduously. But since we clearly can’t count on government helicopters dropping surgical masks on us anytime soon, cloth face coverings are going to be with us for a while. So we’ve had to put our trust in clothing brands, Etsy sellers, or our own ability to create medical devices. And it’s becoming clear that not all of the end products we call “masks” are functionally the same. Those in popular use right now run the gamut from plausibly effective public-health intervention to theatrics, depending on what they’re made of and how they’re used and maintained.

An interesting study of the effectiveness of cloth facial coverings appeared last month in a physics journal. Researchers at Florida Atlantic University compared what happened when coughs and sneezes were blasted into various materials. They found that most any half-hearted attempt at a mask can catch large viral droplets spewing forth from your mouth and nose—though the droplets will still fall onto nearby surfaces if the mask isn’t tight around your chin.

But when it came to stopping airborne viruses from penetrating the mask, some materials were better than others. Bandannas and similarly thin cotton face coverings provided minimal blockage of the aerosolized particles that can shoot through the cloth in a “respiratory jet.” Such jets are created when you speak loudly or cough or sing, and the viral particles can hang in the air and conceivably fill a poorly ventilated room.

The underlying takeaway from the study was that the density of fibers in the cloth makes a big difference in how many tiny droplets travel from your mouth into the air. Surgical masks can be thin because their fibers are arranged to filter out particles, but when it comes to cotton, creating density means layering. Short of running your own physics experiment, a fair rule of thumb is that the blocking power of a cloth mask can be approximated by how hot and suffocating it is. There’s a reason a bandanna is more pleasant to wear than a T-shirt folded over 12 times: The latter lets less air through.

The problem is that the value proposition of layering starts to fall apart if a mask is so thick that it gets sweaty: Cotton and other materials can become less breathable when wet. Moisture from our breath can build on the inside, too, as we breathe harder to cool ourselves. And wetness aside, fabric masks lose value if they’re so thick that they become overly burdensome to wear and people take them off.

Once you’ve calibrated your mask to balance safety and livability, then it’s time to worry about it falling apart. This brings us to washing. Any material degrades with washing, as the fibers grow slightly thinner and farther apart. Avoiding overwashing is especially relevant to masks, because the tightness and integrity of the fibers is essential to their function.

So, in our ramshackle approach to self-masking, there is good reason to think outside the box. One of the things we could be using more to our advantage during this pandemic is time. The virus can hang around for a few days on some surfaces, but it lives longer on hard surfaces such as metal doorknobs than soft ones such as cardboard or cloth. If you waited a week to reuse a mask, I see no reason that you shouldn’t feel certain it was free of the virus. Bacteria and fungi can grow on all sorts of mediums, but viruses need a host. Without one, their days are numbered.

Light is also our friend. The Centers for Disease Control and Prevention recommends washing your mask like you would any other piece of laundry, by machine or hand, and then leaving it to dry in direct sunlight. This latter part may deserve more emphasis than the former. Intense UV rays can kill the virus in less than an hour. This doesn’t mean you’re safe from infection simply because you’re outside, but it does mean that surfaces and materials exposed to direct sunlight will carry the virus for less time than they would in the dark. Sunlight is a tool worth keeping in mind for specific uses like disinfecting makeshift masks, even if it can’t be inserted into people, as President Donald Trump has suggested.

In sum, this may be the surest way to get the safest, longest life out of your mask: Have several masks, made to fit well around your nose and mouth. Make them as heavily layered as you can tolerate. After wearing them for a day or so, or in a high-contact scenario, let them sit for a few days in a sunny, out-of-the-way place. Between the effects of time and light, there should be little need for running a washing machine or going through the hassle of hand-washing your masks. Well, unless they just smell terrible. In that case, maybe it’s your teeth that need cleaning.

If it sounds like I’m making this up based on best guesses, I am. Everyone is. We would ideally all be wearing surgical masks, and disposing of them frequently, but we didn’t prepare accordingly. So for all their flaws, cloth masks are important: Making them effective enough for use in daily pandemic life means we’re freeing up medical-grade masks for people who really need them, especially in places where they are still in short supply, such as the United States. Health-care workers around the world still need proper personal protective equipment more than a random guy named Gene who wants to go to the store to buy snacks.

Supply chains and stockpiles could one day be made robust enough that everyone has ready access to surgical masks, for a low cost if any. No one would need to waste a thought on tearing up an old T-shirt and putting it against their mouth and nose in hopes that it will save their life and the lives of everyone around them.

Americans were warned for years about the shortage of surgical masks, and the federal government ignored those warnings. The Trump administration continues to draw focus away from masks; the president until recently declined to emphasize the importance of wearing one. In January, I wrote “We Don’t Have Enough Masks.” We didn’t then, and still don’t now.


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