From Double Masking to When to Toss Your Cloth Mask: All Your COVID Masking Questions, Answered

With a more contagious variant in the U.S. and updated CDC masking guidelines, we take stock of the available science with immunologist Andrea Love and public-health expert Jessica Steier, of the Unbiased Science podcast.

covid masks

Are your COVID masks up to snuff? Here’s everything you need to know in order to find out. Photo by Brais Seara/Getty Images.

As we approach the one-year anniversary of the first confirmed COVID-19 case in Philadelphia, there are a host of subjects we now know more about than we would ever have liked: aerosols, spike proteins, six-foot distancing guidelines, indoor spread, outdoor spread, ventilation systems and so on. But while we keep learning more about the virus and how it spreads, the guidance on masks since April — the date of the first mask mandate in Pennsylvania — has more or less amounted to “Anything you can get is good enough.”

Maybe that made sense back in the spring, when hospitals were facing an overwhelming PPE shortage and scientists still didn’t know a whole lot about the virus. But according to a series of recent studies, there’s evidence your cloth mask might not be so good at preventing exposure to viral particles.

“Not all materials are made equal,” explains Andrea Love, a Philly-based immunologist who hosts a podcast, Unbiased Science, with Jess Steier, a public-health expert. With the arrival of a new variant that’s thought to be more contagious, the past few weeks have prompted a wave of debate over the best practices for mask wearing. We checked in with Love and Steier to hear the the state of the science and their tips.

Your Cloth Mask May Not Be So Great

A recent study (not yet peer reviewed) of cloth masks looked at how material impacts their effectiveness at blocking droplet particles. At larger particle sizes, the materials — which included a microfiber cloth, a surgical mask, multiple kinds of cotton masks, and a bandana — demonstrated similar filtration effectiveness of upwards of 75 percent. But at smaller sizes, some differences emerged. A microfiber material filtered at least 60 percent of smaller particles, outperforming a surgical mask. A thin cotton mask and a two-ply bandana, on the other hand, each only blocked between 30 and 50 percent of small particles. This led the researchers to recommend a surgical mask topped with a two-layer cloth mask, which they estimated to be at least 75 percent effective at filtration, even for the smallest particles. (A separate study from Northeastern University, which has yet to be published in a peer-reviewed journal, also found wide gaps in protectiveness — anywhere from 30 percent to 90 percent — between different kinds of fabric masks.)

It’s not surprising that some materials work better than others. (In general, Love says, the best cloth masks are made of high-thread-count natural fibers like cotton, followed by dense synthetic fabrics like polyester.) But what is surprising is that while some countries have gone so far as to ban certain homemade or low-quality cloth masks, there hasn’t been much discussion in the U.S. about doing so. Maybe that’s what happens when you have to spend your energy just pleading with people to wear any mask at all.

The problem is that many of us (this writer included) are still rocking cloth masks bought during the early days of the Etsy mask cottage industry. Even if you know what material your mask is made out of, good luck finding a thread count.

So how to determine if your cloth mask is any good? Steier proposes a simple if slightly unscientific test: “Hold the mask up to the light. You don’t want to see outlines of the individual fibers. And tighter is better, of course.” (Scientists at MIT second this.)

Double Masking May Help

What’s better than one mask? Two masks. Go figure. This is the takeaway from a recent CDC study on double masking, or layering a cloth mask on top of a surgical mask in order to shore up the fit and cover any small air gaps. According to the report, a three-ply cloth mask succeeded at blocking only 51 percent of particles from a simulated cough. A regular surgical mask didn’t fare much better, blocking just 56 percent. But when a cloth mask was placed over a surgical mask, the effectiveness of the double mask shot up to 85 percent. (A modified surgical mask, with knotted ear loops to tighten the fit, recorded 77 percent efficacy on its own.)

Researchers found similar results when measuring how effective double masks were at blocking particles originating from the wearer. They calculated that an unmasked person had an 82 percent lower risk when exposed to someone wearing a double mask, and that if both people were wearing double masks, the reduced risk of exposure was as high as 96 percent.

It’s hard to draw universal conclusions about cloth masks from the study, considering that the researchers only tested a single kind of cloth mask. Yours could be better or worse depending on the fit and materials. But there is one obvious takeaway: Mask fit makes a huge difference.

So How Do You Ensure Your Fit Is Good?

The problem of fit isn’t unique to cloth or surgical masks. Even health-care workers who use N95s have to undergo a “fit test” to make sure their masks actually conform to their faces and protect them.

For everyday purposes, Love says, there are four problem areas: the bridge of the nose, the two sides of the cheeks, and beneath the chin. All four spots need to be tight in order for the mask to truly work. (In particular, any mask should contain a wire component on the nose to help seal the gap.) One way to run a sort of natural experiment on mask fit: If you’re wearing glasses outside and they’re fogging up from your breathing, that’s a sign your mask isn’t fitted well. “Those gaps are where your breath will escape, and with that breath comes respiratory droplets,” Love says. “In theory, other people’s respiratory droplets can get into those gaps as well.”

Cloth Masks Deteriorate Over Time

Technically, Love says, you’re supposed to wash your mask after every single use. Even if you haven’t been doing that, you’ve probably been laundering them on occasion. That’s the proper thing to do (especially with warm water and strong detergent, says Love), but it has a negative side effect: Washing ends up stretching the fabric, which could reduce its efficacy over time. Again, the hold-to-the-light test is the best way to tell when you need a replacement.

What can you do if you’re thinking about a mask upgrade? Pre-pandemic, it was almost unheard-of to reuse surgical masks, but the earlier PPE shortages forced health-care workers to get creative. Love says that if you can find surgical masks, you can wear them once, then place them in a paper bag for a week to “give time for any potential pathogens to be inactivated.” At that point, the mask is safe to reuse, although after eight hours of total use, it should be thrown away. That might sound labor-intensive, but you could get a little rotation going — seven surgical masks, seven paper bags — and have a clean one ready every day of the week. You could also seek out N95 masks. Apparently there are more than a few companies with hefty stockpiles (though you should be wary of fakes).

What About the Variant?

Scientists don’t fully understand why the new coronavirus variants are more transmissible than the original strain of virus. But they do know that even as overall cases are falling in the U.S., the case rate of the new variant from the U.K. is actually doubling every 10 days. Most estimates suggest that the U.K. strain will become the dominant strain here by March.

It’s too early to know how that will impact the current downward trend of cases, but it’s not hard to recognize the implications for your mask. Imagine your current mask blocks 40 percent of all particles. With a less transmissible virus, maybe that was enough to limit your exposure and prevent you from getting sick. But if the more transmissible strain means it takes less exposure to get sick, that old mask may no longer cut it. For her part, Love says, she’s not taking any chances: “I double-mask indoors all the time, no matter what.”