Illustration by Hunter French

Masks Alone Don’t Make You Invincible

Covering your face can help combat the coronavirus. But some scientists fear people now believe masks of any quality are foolproof defenses—and they're being labeled as "anti-mask" for saying so.
August 11, 2020, 1:00pm

Michael Osterholm wears a cloth mask when he goes outside. He supports their use and believes they may help slow the spread of tide of the coronavirus. But his organization, the Center for Infectious Disease Research and Policy at the University of Minnesota, or CIDRAP, has dealt with a deluge of hate mail recently from people who believe it doesn't believe in them enough. Some have even accused Osterholm and others of contributing to the "death of thousands of humans"—something he has a hard time understanding.


“I’m on a team that’s working on a washable N95 mask that could be used up to 300 times. CIDRAP is finishing a study showing that 26 percent of people aren’t covering their noses when they use masks and encouraging them to do so. I wear a mask when I have to go out,” Osterholm said. “I’m not sure how any of that is anti-mask.”

The root issue is that Osterholm's scientific views do not fit neatly into one of the main debates of the day: Are masks good or bad? Early on, there was a thought that COVID-19 was transmitted primarily through larger droplets from coughs and sneezes, which cloth masks could catch. But many scientists now believe smaller particles known as aerosols also play a significant role in the transmission of SARS-CoV-2, the virus that causes COVID-19. Osterholm and others at CIDRAP have long studied how well different types of masks filter such aerosols, which are emitted when people exhale, be it through breathing, talking, or singing. And while Osterholm believes cloth masks may reduce the spread of the coronavirus, he is concerned that some have overstated their ability to do so.

This places Osterholm and CIDRAP at the center of a debate that increasingly doesn't have one anymore. “I seem to be somewhere in the middle on this issue,” he said, “but somehow that’s considered an extreme position.”

As an epidemiologist, Osterholm has spent decades researching infectious diseases, serving from 2001 to 2005 as a special advisor to the secretary of the Department of Health and Human Services, including on issues like public health preparedness. Now a fierce advocate of social distancing in the COVID-19 era, he is worried that an outsized faith in cloth face coverings might lead some to falsely believe a mask is akin to a fortified shield.

“I seem to be somewhere in the middle on this issue, but somehow that’s considered an extreme position.”

As the U.S. has continued to reopen amid a deadly pandemic, masks have offered many people what feels like a simple way to responsibly return to something resembling normalcy. Multiple studies have found a correlation between early, widespread mask use and a lower COVID-19 death rate, part of what led a shift in emphasis from social distancing to covering up. In July, CDC director Robert Redfield said at a press conference that “if all of us would put on a face covering now for the next four weeks, six weeks, we could drive this epidemic to the ground.” While the suggestion could be seen as an improvement over President Trump’s own pronunciations, it also portrayed masks as a one-stop solution to COVID-19, rather than what Osterholm and others believes they should be: one part of a broader action plan that should include social distancing and avoiding prolonged indoor contact.

Versions of Redfield’s train of thought have become commonplace on the internet. One recent meme that’s floated around depicts two people, one of whom is a “COVID-19 carrier,” the other is a “contagion risk.” The contagion risk goes from high to low based on who is wearing the mask. The risk is highest when only the “contagion risk” is wearing a mask and lowest when both people are. The oversimplified graphic doesn’t say what type of mask is being used, the length of time the two were in contact, or if they’re indoors or outdoors—all factors when talking about aerosolized transmission.


Joshua Santarpia, a microbiologist who studies biological aerosols at the University of Nebraska Medical School, believes such memes are misleading. He explained,  “If two people are talking in a room, both wearing masks made from T-shirts, and one of those people has the virus, the other is very likely to get sick if they stay in the room long enough. That transmission is much less likely if the two are outside, even if they’re not wearing masks.”

“If two people are talking in a room, both wearing masks made from T-shirts, and one of those people has the virus, the other is very likely to get sick if they stay in the room long enough.”

Scientific research can and often does deliver nuanced and even conflicting information, especially when dealing with a novel virus. That scientific reality clashes with attitudes in an increasingly polarized country. The problem has become particularly burdensome to scientists working in real time to address the ongoing public health crisis. Questions like which masks work, and how well they do, will remain critical in best protecting the American population.

In early April, Osterholm consulted with infectious disease experts at the National Academies of Sciences, Engineering, and Medicine as they prepared a “rapid expert consultation” on “the effectiveness of homemade fabric masks worn by the general public to protect others.” They reviewed filtration studies from a span of 12 years and found that there wasn’t enough evidence on aerosols and cloth face coverings to say conclusively one way or the other, acknowledging that efficacy would likely depend on “how the masks are made and used.”

“This isn’t a pro-mask, anti-mask discussion.”

Fleece, scarves, and bandanas, for example, are not great at trapping aerosols. Masks made entirely out of cotton T-shirts are better, but not as effective as several layers of 100 percent cotton and silk . Better yet are layers of 100 percent cotton, silk, and spunbound polypropylene. Fit is also crucially important:  If there are gaps around the sides of your masks, aerosols are going to find their way in and out no matter the material.

“This isn’t a pro-mask, anti-mask discussion,” Osterholm said. “This is about what the science tells us about the efficacy of cloth face coverings, and how much of a role they play in slowing transmission.”


In July, 239 scientists from around the world signed an open letter to the World Health Organization (WHO), writing that it was "time to address airborne transmission of COVID-19." Early in the pandemic, WHO said that the virus was primarily transmitted through droplets, the relatively large particles that are emitted when people cough or sneeze and quickly fall to the ground. Back then, cloth masks of any sort started to seem like an effective tool, since they could successfully block such droplets. But aerosols are a smaller kind of particle—one that is emitted when we cough and sneeze, but also when we breathe, talk, or sing. Because of their small size, aerosols can stay in the air much longer, allowing them to travel further and potentially more easily slip through someone else’s mask. If it’s both aerosols and droplets that are transmitting the virus, then the calculus on masks might need to shift.

There is evidence to suggest that even a basic mask made from a cotton T-shirt might limit the number of viral aerosols emitted into the environment by an infected person. But according to William Ristenpart, a professor of chemical engineering at UC Davis, “it’s still an open question as to exactly what percentage of expiratory aerosol particles are blocked by a cotton mask.” People like Osterholm and Ristenpart are working to find an answer, but there’s no consensus about exactly how much cloth face coverings slow transmission. Ristenpart’s own work, which is undergoing peer review, suggests that cotton face coverings are reasonably effective in hindering particle emission. But his team also found that some cloth masks emitted tiny fibers from the mask itself, confounding the measurement.

Because virulent anti-maskers have so politicized the issues—throwing dramatic fits in grocery stores and screaming at strangers—even suggesting the potential limitations of cloth masks can come across as denialism.

Even the experts who are more skeptical of masks’ efficacy say people should wear one, so long as it’s not at the expense of other practices, like social distancing. Any tool that provides even the possibility of slowing transmission should arguably be utilized by as many people as possible. Osterholm and Lisa Brosseau, his colleague at CIDRAP and an expert on respiratory protection and infectious diseases, said they’d agree with that, up to a point.

But because virulent anti-maskers have so politicized the issues—throwing dramatic fits in grocery stores and screaming at strangers—even suggesting the potential limitations of cloth masks can come across as denialism. And when trying to convey unknowns and nuances in a polarized discussion, there’s a risk of bad actors deliberately misconstruing an expert’s remarks, and well-meaning people misunderstanding the experts. Ristenpart said his team has been very concerned that people will take the part of his study about some cloth masks emitting micron scale fibers and say, “‘Look, masks are bad!’ That’s not what we’re saying,” Ristenpart said. “We’re saying something very distinct from that.”


Osterholm and Brosseau have faced significant criticism for some of their statements around masks. At times, their comments have been explicitly mischaracterized; other times their comments could reasonably be seen as too dismissive for people trying in good faith to understand the issue. Either way, their vocal concerns about people’s overconfidence in cloth face coverings have led to  praise and anger from people on each side of the issue.

Osterholm admits his own messaging hasn’t always been perfect. In March, he sat down with podcast host Joe Rogan to discuss COVID-19 and other infectious diseases. Rogan asked if the general public wearing gloves and masks was “nonsense,” and Osterholm replied, “largely, yes.” He went on to discuss his belief that the primary mode of transmission were aerosols, for which you’d ideally use something like an N95. (That message may not have landed with Rogan, who in June called people who wear masks “bitches.”)

Then, in an April 3 interview with WCCO, a radio station in Minneapolis, Osterholm said that people should wear cloth masks if they wanted to, but neither he nor his colleagues thought it would have a “major positive impact.” Such comments led to accusations that CIDRAP was “using their platform to promote misinformation to the public.”  Osterholm didn’t see it that way, saying he was trying to be honest with the public about the limitations of cloth face coverings. “I think early on, what we were trying to say is, ‘Be careful. You're overselling what we know about the efficacy of these face coverings,’” Osterholm said. Now, he admits he could have been more “artful” in communicating that message. “I'm just trying to keep people from using them as their sole protection.”

“If you don’t want to get pregnant, the most effective way to prevent it is staying home by yourself. Masks are prophylactic. They’re not universally 100 percent effective.”

Since that time, the issues surrounding masks have extended out from the scientific realm and into the political world. That politicization, pushed by politicians and conspiracy theorists, on the right, has led to a lack of patience for nuance more broadly. Osterholm said he has since been told by friends in the media that they won’t have him on their shows because he comes off as too “anti-mask.”  In a July profile of Osterholm in Mpls. St.Paul Magazine, the author wrote, “I realized Osterholm was no longer America’s midwest voice of reason when more than one friend synthesized his message as that of ‘the anti-mask guy.’”

The controversy reminds Osterholm of what he describes as “the hardest time in my professional life.” In 2011, he published a paper questioning the stated efficacy of the seasonal flu vaccine. At the time, the vaccine was estimated to be 70-90 percent effective. He reviewed 12 seasons of controlled trials of the vaccine and found that the effectiveness was, at best, around 50 percent for the general population, and extremely low for those over 65 years old.


“There were so many people who were dogmatically so angry at me,” Osterholm said. “Like I might as well have been saying vaccines cause autism or something.” But the CDC did their own studies which corroborated his findings, and now “we’ve had more action towards getting a universal flu vaccine than we have in the last 40 years.” In 2019, the FDA also approved a flu vaccine specifically for seniors. Without a more accurate picture of the effectiveness of the prior vaccine, there would have been no reason to invest in creating a better one.

For her part, Brosseau’s comments have been used out of context by right-wing publications to argue for positions she doesn’t support. In April, a few weeks after Osterholm spoke to the radio show, Brosseau told Infection Control Today the same thing: that cloth masks were fine, but she didn’t think they did “much good” adding, “So we should continue to do social distancing as much as we possibly can.” The conservative publication The New American quoted the first part of Brosseau’s statement, but neglected to include her recommendation for continued social distancing. Instead, the author alluded to a right-wing conspiracy theory about “vaccines made by globalists such as Bill Gates,” and argued that “forcing law-abiding Americans to wear anything is an overreach of government authority.”

Brosseau told VICE News she doesn’t think mandating masks is an overreach of government authority. If the world had an unlimited supply of the right masks, she’d be thrilled about mask mandates. “If everyone had fit-tested N95s?” she asked. “That would be great.”


Overstating the safety of cloth masks could be especially dangerous for workers, said Brosseau. She has spent much of her professional life researching how to protect workers from hazardous aerosols in the workplace, and said that it’s possible that cloth face coverings can prevent transmission for short periods of time, but we don’t know for sure how long that lasts.

To illustrate her claim, Brosseau pointed to one recent well-publicized incident in a Missouri hair salon. Over nine days, customers in the salon had their hair cut for 15 to 45 minutes by a stylist who later tested positive for the coronavirus. Staff and customers all wore different kinds of face coverings, including cloth masks, and no customers were infected with the virus. To Brosseau, this suggests that face coverings are effective indoors for a limited amount of time.

But she also believes cloth masks are unlikely to protect workers who are in an enclosed space for hours on end, a theory that was also borne out at the Missouri salon, where the COVID-positive stylist infected another stylist because they were in the same enclosed environment for multiple hours. “I don’t know if it’s 30 minutes or two hours, but the longer you’re in a room with someone who has the virus, the more opportunity there is for transmission,” Santarpia said. There’s evidence to support the belief too. In July, Amanda Wilson, an environmental health sciences doctoral candidate at the University of Arizona, published a study that found “the more time a person spends in an environment where the virus is present, the less effective the mask becomes.”

“I’m worried we're turning a knife in the back of workers.”

In stories about the salon, however, very little was mentioned about the stylist who became infected. The headline of The Washington Post story read “The outbreak that didn’t happen: Masks credited with preventing coronavirus spread inside Missouri hair salon.” Brosseau worries that these kinds of stories are being used to push workers back to unsafe environments, and that it’s important to highlight the difference between what happened with the clients and stylists. “I’m worried we're turning a knife in the back of workers,” she said.

In the media, the focus on masks has often eclipsed other, more significant factors in COVID-19 transmission, like whether someone has recently attended a large, indoor event. After Herman Cain died last month from COVID-19, which many suspected he contracted at a Trump rally in Tulsa, Oklahoma, the New York Times asked, “Will Herman Cain’s Death Change Republican Views on the Virus and Masks?” Dozens of other headlines about Cain’s  death mentioned his anti-mask stance too. The stories seemed to suggest that the major risk factor was the lack of masks at the event, rather than the fact that he had sat in an enclosed space with 6,000 people talking and cheering for at least two hours.

“If you don’t want to get pregnant, the most effective way to prevent it is staying home by yourself,” Santarpia said. “Masks are prophylactic. They’re not universally 100 percent effective.” For rally attendees, the risk may have been heightened by lack of masks, but a lack of masks didn’t create the risk.

Prior to the Tulsa rally, as cases in the Oklahoma area were spiking, MSNBC’s Brian Williams asked Osterholm if the event was “public health malpractice.” After months of watching his words get misrepresented, he worried that anything he said  about a Trump rally would be contorted and politicized. Osterholm offered a theoretical answer instead.

“If all four Beatles were able to be back tonight in a large indoor area concert in a place like Tulsa, I wouldn’t go. I wouldn't want any of my loved ones to go,” he replied. “That's how we have to understand this situation.”