covid masks

In many places around the United States, wearing a mask is a must. Failing to wear one might garner a few dirty looks in the grocery store or on the street—or, more than a few. But what does the science say?

It’s a bit hard to remember now, especially if you live in the New York area, the center of the pandemic. But there was a time when people who were wearing masks were bad—because we all needed to leave masks for front-line workers who needed them more than us. Then it all switched suddenly:  In early April, the United States Centers for Disease Control  changed its guidance on cloth face masks, recommending that they be worn in public settings “where other social distancing measures are difficult to maintain.”

In many places around the country, masks are not just recommended—they’re the law.

Multiple states followed the C.D.C.’s guidance with new rules requiring that masks be worn in public. At the time of publishing, 14 states have instituted mandatory mask-wearing policies in all public places, while all but six states require masks in some situations.

Increasingly, support for mask wearing has become a political issue. President Trump has rejected mask wearing as unnecessary, even refusing to wear a mask in settings where it is otherwise required.

While masks have been adopted by some states as a necessary precaution to prevent the spread of Covid-19, the debate within the scientific community over their effectiveness rages on.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, prominently questioned the scientific justification for wearing masks in an episode of his podcast released last week. Osterholm argues that recommendations for mask-wearing are not based on real science—instead, he says, they are based on flawed studies and unhelpful data.

“The public message on cloth mask effectiveness that is provided to the medical community, public policy leaders and the general public must be based on sound scientific data and currently it is not,” Osterholm said. He lays out his case in this podcast, with transcript and citations.

Another expert’s opinion

Babak Javid is a professor at Tsinghua University’s medical school in Beijing and an infectious disease consultant at Cambridge University hospitals. He advocates for universal mask-wearing, and has clashed with Osterholm on the issue in the past.

Javid disagrees with Osterholm on one of the finer points of Covid-19 — how the virus can spread through the air. Osterholm believes that the virus spreads in aerosol form, or in very small particles from one’s breath that tend to linger and travel longer distances, while Javid believes that the virus mostly spreads through larger droplets propelled by coughing or sneezing. Read more about his thoughts here.

The distinction is important: If the virus spreads as an aerosol, masks are probably  much less effective in preventing the spread, although some studies indicate that surgical masks (which are different from commonly used cloth masks) can partly prevent infections from an aerosol virus.

Remember that there are three main types of masks: N95 masks, surgical masks and cloth masks. N95 masks are the most effective at filtering, but are reserved for healthcare workers. Surgical masks, which are generally thought to be more effective than cloth masks, are also scarce. Cloth masks are what you see on the street generally: Your friends and neighbors with hand-made masks, or bandannas or loose-fitting masks with gaps to the side and top and bottom.

Controlled studies of mask use to prevent the spread of viruses are hard to come by — only one has been done with influenza, and it found that cloth masks were only three percent effective. But, Javid says, many more studies have shown that cloth masks filter more effectively, with data wildly varying from 10 to 70 percent effectiveness at filtering particles (when not on someone’s face).

Javid adds that concerns over the true effectiveness of masks miss the point. “Measures that reduce risk by a little bit, if applied across the whole population, are going to have a much bigger effect than highly effective measures for a very small number of people,” he said. He is quick to note that other protective measures like hand washing and social distancing are not backed by conclusive science either.


Javid is not alone in his support for masks: Many in the scientific community have expressed their support for mask wearing.

In a letter posted by the organization Masks4All, over 100 academics affirmed that masks could be “amongst the most powerful tools to stop the community spread of COVID-19,” and asked that governments require masks be worn in public settings. The letter cited a non-peer-reviewed summary of evidence which concluded that, among other things, masks were effective at controlling the spread of Covid-19.

Osterholm, who refers to Masks4All as a “misinformation campaign” in his podcast, objects to this conclusion—he says that the only studies examining masks to prevent the spread of disease are out of date and do not support Mask4All’s conclusion.

Dr. Daniel Morgan, who signed the Mask4All letter, is an epidemiologist at the University of Maryland. He says that Osterholm is right that there is little good data, but that masks should be widespread anyway.

“There are some theoretical reasons it may work but we don’t have real life data of effectiveness,” Morgan wrote in an email. But, he added that “universal masking is the least harmful part of the very harmful shutdowns,” referring to schools and businesses closing.

Anna Kaltenboeck, a health economist at Memorial Sloan Kettering Cancer Center who signed the letter, says the trouble is how little is known about how the virus spreads. Kaltenboeck says that masks might help stop the spread, and have few drawbacks.

“It is plausible that you can prevent some spread (of the virus), but how much a mask does that is unknown,” Kaltenboeck said in an interview. She agrees with Osterholm that “you don’t want to reassure too much during a pandemic.”

The precautionary principle

The idea of masks having potential benefits and few harms was articulated in an article in the medical journal BMJ.

Trisha Greenhalgh, a health science expert at Oxford University, and several other experts advocate for the use of the precautionary principle. The precautionary principle is the idea that we should sometimes make policies without strong scientific support in order to potentially avoid harm.

Greenhalgh applies this principle to the Covid-19 pandemic: Because of the profound risks posed by the spread of Covid-19, masks should be universally worn, even though there is not strong scientific evidence.

“Masks are simple, cheap, and potentially effective,” the authors wrote. “We believe that, worn both in the home (particularly by the person showing symptoms) and also outside the home in situations where meeting others is likely (for example, shopping, public transport), they could have a substantial impact on transmission with a relatively small impact on social and economic life.”

What should you do?

Here are some recommendations:

  1. Wear a mask: It’s required by law in many states, it can make those around you feel more comfortable and most likely prevents the spread to some degree. All of the experts quoted above wear masks in public.
  2. Fit is important: there should not be any gaps between your mask and your face for particles from your breath to escape out of. That means you shouldn’t wear a loose-fitting mask or a mask that only covers your mouth and not your nose.
  3. Material is important: studies show that the most effective material is a combination between cotton and silk or chiffon. Also, cloth with a tight weave (or a high thread count) is much more effective at filtering.
  4. How your mask is made is important: Layering cloth is better than a single sheet, and your mask should be made to fit tightly on your face (going back to fit again).
  5. Do not let masks be an excuse to relax. Even while wearing a mask, maintain social distance, wash your hands regularly and avoid groups of people whenever possible. Staying home is ultimately the safest thing you can do.

Ben Glickman

Ben Glickman is a student journalist at Brown University with experience with data analysis, investigative tools and audio storytelling. He is passionate about holding power...