Quotes from Experts

Covering your face during the COVID-19 pandemic

SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use these responses in news stories, with attribution to the expert.

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May 14, 2021


What is the scientific or public health basis for the new CDC recommendations that fully vaccinated people can go unmasked?


“This recommendation was based on the continuing decline and trajectory of cases, examining the efficacy of the vaccine products available in the US, and our current understanding of how transmission is occurring (i.e., understanding how the virus spreads). It also helps provide a pathway to ‘a new normal’ to indicate that, by taking certain actions, an individual can begin to slowly resume activities they were engaging in pre-pandemic.” (Posted May 14, 2021)

Rupali J. Limaye, PhD
Associate Scientist, Global Disease Epidemiology and Control, Johns Hopkins University

“This new guidance is based on multiple studies that have shown the profound effectiveness of the vaccines to prevent both COVID-19 disease and transmission in the real world.  For instance, vaccines are 95% effective in preventing symptomatic COVID-19 in roll-out programs in Israel, 90% effective in first-line responders and health care workers in the US, and 97.4% effective against severe disease, even against the B.1.351 and B.117 variants, in Qatar. Moreover, there is ample evidence at this point that vaccines massively reduce asymptomatic infection (and, thereby transmission), from rates of 86% to 92%, across multiple studies. Therefore, if a vaccinated individual is highly protected and highly unlikely to transmit the infection to others after vaccination, lifting masking and distancing requirements for this population makes sense. Moreover, since masks protect the wearer, the unvaccinated will be protected by their own mask in an indoor setting.” (Posted May 14, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

Is dropping mask requirements for the fully vaccinated an effective way to encourage vaccination?


“On one hand, people may feel more incentivized to get the vaccine if they see that by getting the vaccine, they no longer have to wear a mask and can resume pre-pandemic activities. On the other hand, it may not be enough of an incentive to get the vaccine, and may signal to people that they can go maskless while being unvaccinated, as there is no way to know who is vaccinated and who is not. This could lead to a situation where those that are unvaccinated may be maskless in settings where there are other unvaccinated individuals, leading to higher risk of exposure.”  (Posted May 14, 2021)

Rupali J. Limaye, PhD
Associate Scientist, Global Disease Epidemiology and Control, Johns Hopkins University

“Yes, it can be highly motivating for individuals on the fence about whether to get vaccinated that such requirements will go away once vaccinated.” (Posted May 14, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

April 27, 2021


What do we know about the likelihood of SARS-CoV-2 transmission outdoors?


“The risk of outside transmission is very low because viral particles disperse effectively in the outside air. A study in Wuhan, China, which involved careful contact tracing, discovered that just one of 7,324 infection events investigated was linked to outdoor transmission. In a recent analysis of over 232,000 infections in Ireland, only one case of COVID-19 in every thousand was traced to outdoor transmission. And a scoping review from the University of Canterbury concluded that outdoor transmission was rare, citing the opportunity costs of not encouraging the public to congregate outdoors. Overall, transmission is around 5000 times less likely to happen outside than inside.” (Posted April 27, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

“There is a significant amount of epidemiological data available that would suggest that outdoor transmission is unlikely. Further, there are several studies indicating that viral aerosols are likely to decay more rapidly outdoors. Together, this suggests that risk outdoors is low, and that reducing restrictions on mask wear during outdoor activities is reasonable.”  (Posted April 27, 2021)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

“The CDC just changed the guidelines today, and what they’re saying is that if somebody is outside, you don’t have to wear a mask. And that’s a relief for people who do a lot of outdoor activities. The ambiguity is gathering size, because a lot of people are worried about what gathering size they’re talking about.”  (Posted April 27, 2021)

Asim Shah, MD
Professor of Community and Family Medicine, Professor of Psychiatry, Baylor College of Medicine

Based on the new CDC guidance, how should people decide what size “small group” is acceptable for maskless gatherings outdoors?


“For vaccinated people, the group can be quite large and likely depends on case rates in your region (case rates are falling across the U.S. with a -20% decrease in new cases per day over the past 2 weeks in the U.S.).  This is because vaccines are extremely effective in real-world settings. The CDC keeps track of breakthrough infections—where people contract COVID-19 after vaccination—in the U.S and the rate remains astoundingly low even while COVID-19 is still circulating (32,151 cases across the U.S. today). Out of 87 million fully vaccinated people, there have only been 5079 symptomatic breakthroughs (0.005%), only 0.0003% hospitalizations related to COVID-19, and only 0.00009% deaths related to COVID-19. Vaccines are incredibly effective under real-world conditions.

“The risk to unvaccinated people is higher and depends on the case rates in your region. I would recommend that unvaccinated people in crowds or packed situations put on their masks.

“I think this signals a great time in the pandemic in our country. However, this is a terrible time in the pandemic for India, where only 8.8% of the population has had their 1st dose of the vaccine. Cases stay low in countries that are opening up, like Israel and the United kingdom, if vaccination rates are high—Israel has 60% of their population vaccinated with their first dose and the United Kingdom has 51% of the population first dose vaccinated (the US is at 42.7% first dose vaccinated). Relaxing masking outdoors will not lead to increased cases in our country as we continue to vaccinate, but my heart bleeds for India and we should do everything we can to help this country and other regions of the world who do not have the same access to vaccines.”  (Posted April 27, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

“This is a pretty vague recommendation, and it requires people to make their own risk assessment. People have to make decisions about how closely they might interact with others at gatherings. There’s not a clear line, and no answer will be without risk, so it’s up to the individual to make the best decision they can.” (Posted April 27, 2021)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

“The definition of ‘gathering’ is vague, and what the CDC is saying is that a large gathering is considered large when you have many people from multiple households in a private or a public setting. So, if you have multiple people from different households, you have maybe twenty-five or thirty people, that would be considered large, whereas the same number of people from the same household would not be considered large. So it’s not an absolute number, it’s how many households you are covering. Because each household brings an added chance of COVID.” (Posted April 27, 2021)

Asim Shah, MD
Professor of Community and Family Medicine, Professor of Psychiatry, Baylor College of Medicine

Should partially vaccinated people follow the same masking guidelines as unvaccinated people?


“There are two principles involved to changing the outside mask guidelines: One is that COVID-19 transmission outdoors is very low. The second is that—with more and more Americans getting vaccinated—recommending that vaccinated people could congregate outdoors without a mask can be a motivating factor for those on the fence about masking. The World Health Organization ,even prior to vaccines, stated that masks are not necessary outside unless it is impossible to maintain physical distancing (defined as 1 meter=3.28 feet by WHO guidelines), so unvaccinated people should be able to unmask outdoors if they can maintain three feet of distance from others. For situations such as rallies and packed outdoor events, I would recommend unvaccinated people mask until case rates are lower than 5 per 100,000 in your region. And I would recommend partially vaccinated people follow the same guidelines as unvaccinated.” (Posted April 27, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

“Partially vaccinated individuals have some antibodies, have some immunity to the virus, and some protection against infection and disease. That said, it’s the safest option to behave as if you are unvaccinated, if you have only had a partial vaccine.” (Posted April 27, 2021)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

“Partially vaccinated people are considered nonvaccinated. So you are only considered vaccinated two weeks after your last dose of vaccine. Partially vaccinated there is no difference than nonvaccinated, so you should follow the same guidelines as a nonvaccinated person.” (Posted April 27, 2021)

Asim Shah, MD
Professor of Community and Family Medicine, Professor of Psychiatry, Baylor College of Medicine

How might differences in public masking behavior between vaccinated and unvaccinated people impact wider masking behavior or public perceptions of what is safe?


“I know that many public health practitioners have argued the ‘slippery slope’ principle that we will not be able to mask indoors if guidelines change to allow unmasking outdoors. But I argue that Americans know when they are outside and can understand this nuance. Moreover, since outdoor transmission is so low anyway, even for the unvaccinated, I am not concerned this will increase case rates or public perception of what is safe. Indeed, I think following the data on how low the risk of outside transmission is and being consistent with WHO guidelines increases trust in our public health guidelines.” (Posted April 27, 2021)

Monica Gandhi, MD, MPH
Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

“It’s certainly something to consider. I believe that people need to take individual responsibility for their own safety. Everyone needs to make their own personal risk assessment, based on vaccination status or previous infection, co-morbidity factors, and situation. Further, they need to appreciate that someone else’s risk calculation may be different and so they may behave differently. As long as we establish some general guidelines, there is room for variation.” (Posted April 27, 2021)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

“One of the reasons that the CDC issued these guidelines is to give people incentives to go for vaccination, because now we have twenty percent or more of Americans who don’t want the vaccine. So we want to give people an incentive that if they are vaccinated, they can go out and don’t have to wear a mask and are okay. So that’s one of the reasons.

“The problem with masking that we are facing right now is the concept of autonomy. A lot of people do not want to mask because they feel that, oh, it’s an infringement of my rights. But this is a public health issue, so we need to think differently.” (Posted April 27, 2021)

Asim Shah, MD
Professor of Community and Family Medicine, Professor of Psychiatry, Baylor College of Medicine

January 29, 2021


Is the primary purpose of masks to protect the wearer or their neighbors? Can both be achieved simultaneously?


“Masks protect both the wearer and others. Masks are able to filter out aerosols/particles in both directions, although they typically work better in the outward direction because of humidity behind the mask and the fact that it’s so close to the jets of air coming out of your nose and mouth when you breathe and talk.” (Posted January 29, 2021)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“We are asking masks to do double duty. They are simultaneously protecting the wearer from particles that may be carrying active virus and protecting others from virus that may be emitted by infected people. Since virus can be shed by people days before they experience any symptoms, it is important for all of us to be wearing masks. The exception to this is masks with valves. Those masks are designed to protect the wearer from particles, but allow exhaled air to bypass the mask, making them ineffective at protecting others.” (Posted January 29, 2021)

Loretta Fernandez, PhD
Associate Professor of Civil and Environmental Engineering and Marine and Environmental Sciences, Northeastern University

“Masks protect the wearers and their neighbors simultaneously. Filtration works for both inward and outward directions . However, it is more critical for the symptomatic and asymptomatic patients to wear masks to prevent the emission of virus-containing aerosols and droplets.” (Posted January 29, 2021)

Yang Wang, PhD
Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology

How much does mask fit matter, for all masks, and what should someone do to ensure they have the best fit possible?


“Mask fit is extremely important—as important as filtration ability. If air can easily pass through gaps between the mask and your face, then it’s not being filtered and it’s like having holes in your mask. You should feel the mask sucking up against your face when you breathe in. You can improve fit by using a mask that fastens around the head rather than the ears, because you can get a tighter fit, and by using a mask with a metal nose bridge that you bend carefully to the shape of your nose.” (Posted January 29, 2021)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“In terms of protecting the wearer, masks are only effective if the air we breathe actually goes through the mask. The Occupational Health and Safety Administration requires that anyone using an N95 respirator for work—such as those who work in health care settings—pass a fit test to make sure that the specific brand and size of respirator assigned to the worker does not allow air to slip past. This usually occurs through gaps around the nose or cheeks or is caused by facial hair.

“In our tests of fabric masks, we added an elastic overlayer—either a section of nylon stocking or a gaiter—over the top of a fabric mask. We found that performance with the elastic overlayer, in terms of removing particles from the air the wearer is breathing, was improved in half of the 50 masks tested. The particle removal efficiency was often improved by more than two times (e.g., from 28% particle removal to 73% particle removal). We also tested other elastic layers, such as sections of tights and gaiters, that could be worn over masks and found that they had the same effect of cutting off routes for air to bypass the mask. These also worked, although the tighter the fit, the more improvement was observed. Interestingly, we found that by using this elastic layer, many fabric masks could be made to work as well as an ill-fitting N95.

“All of that said, it would be difficult to wear an elastic layer over any mask all day long.” (Posted January 29, 2021)

Loretta Fernandez, PhD
Associate Professor of Civil and Environmental Engineering and Marine and Environmental Sciences, Northeastern University

“Mask fit is very important. An N95 that does not fit the wearer may perform worse than a cloth mask. To quickly check mask fit, the wearer should exhale air as hard as he or she can, and then check if the exhalation causes the blinking of eyes or fogging on the glasses. If it does, then the wearer needs to adjust the mask or change to another mask.”(Posted January 29, 2021)

Yang Wang, PhD
Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology

Does it improve protection for individuals with cloth masks to double up and wear two?


“In most cases, two masks provide better protection than one, especially if one happens to be good at filtering (like a surgical-type mask with ASTM certification) and the other provides a great fit. Even two cloth masks are better than one, usually, although you need to pay attention to breathability. If it’s too hard to breathe through the mask, then it’s more likely that air will leak through gaps around the sides.” (Posted January 29, 2021)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“As long as the air is going through the masks, rather than around them, protection is improved. For example, if one mask removes 50% of the particles, the second mask could remove 50% of the particles that made it through the first mask, bringing the overall particle removal to 75%. If the second mask functions to improve the fit of the first mask, we would also expect to see improved particle removal. We have not, however, specifically tested out double masking with two non-gaiter, ear loop cloth masks.” (Posted January 29, 2021)

Loretta Fernandez, PhD
Associate Professor of Civil and Environmental Engineering and Marine and Environmental Sciences, Northeastern University

“Yes, it will improve protection to double up cloth masks. In our study, we found that the thicker the mask, the better the filtration efficiency. However, breathability also matters. A mask with a poor breathability will lead to air leakage (a poor fit), and the protection will be worse. The wearer should check if the doubled masks can be breathed through and if they lead to a poor fit.” (Posted January 29, 2021)

Yang Wang, PhD
Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology

“It is pretty safe to say that having more covering your mouth and nose is more protection than less. So, more layers of material will generally provide more protection.” (Posted January 29, 2021)

Laura Forsberg White, PhD
Associate Professor of Biostatistics, Boston University

Should everyone wear technical masks (N95, KN95) instead of other types of masks if enough become available?


“If high-quality masks were widely available, then yes, I think everyone should wear them because such masks would reduce transmission. Having an N95 does not guarantee great protection, though, unless it fits well. You can get protection similar to that of an N95 with a good cloth mask that has a good filter in it. Studies have found that the following materials are high-performing filters, although you may need to improvise some of these from materials originally intended for other purposes because they are not widely available as mask inserts: high efficiency particulate air (HEPA) filters, surgical mask material (ASTM certified), HVAC filters rated MERV 13 or higher, vacuum cleaner bags.” (Posted January 29, 2021)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“In our work, we found that many cloth masks worked as well as or better than some KN95s due to fit issues. A well-fitting N95 would protect the wearer more than any cloth mask, but may not be necessary for stopping community transmission. Just as I believe it would be difficult to wear an elastic layer over a fabric mask all day long, it would also be difficult to wear an N95 all day long. As we saw in our data, wearing an N95 loosely for comfort, as I see many people doing, provides little more protection than regular medical procedure masks or most multi-layered cloth masks.” (Posted January 29, 2021)

Loretta Fernandez, PhD
Associate Professor of Civil and Environmental Engineering and Marine and Environmental Sciences, Northeastern University

“There is no need for the general public to wear technical masks. A surgical mask is sufficient to filter out almost all of the virus-containing aerosols and droplets. Masks made of densely woven cloth are also effective at stopping the larger droplets. But, because there is not a direct way for people to test the filtration efficiency of their own cloth masks at home, surgical masks are recommended if they are available.” (Posted January 29, 2021)

Yang Wang, PhD
Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology

“At this point it is not clear that is necessary, and it certainly depends on the type of activity. For instance, if someone is outside on a run a mask like this is not really necessary since the risk of transmission is quite low. Healthcare workers should always have this level of protection.” (Posted January 29, 2021)

Laura Forsberg White, PhD
Associate Professor of Biostatistics, Boston University

How does vaccination status relate to mask wearing?


“People should still wear masks even after they are vaccinated. Universal masking is needed until COVID-19 is under control.” (Posted January 29, 2021)

Yang Wang, PhD
Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology

“When we think about an infectious disease like COVID-19, we cannot think about individuals in isolation. Research is showing us that the available vaccines right now (Moderna and Pfizer) are very good at making it so people do get not sick from the virus, SARS-CoV-2. However, what is still not clear is if vaccinated people can still be infected with the virus and transmit it to others without knowing. Essentially, we do not know if the vaccine can make someone more like an asymptomatic case. Until we know for sure, even those who are vaccinated should be vigilant in wearing masks.” (Posted January 29, 2021)

Laura Forsberg White, PhD
Associate Professor of Biostatistics, Boston University

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July 8, 2020


What do we know now about wearing masks and COVID-19 transmission that was not clear earlier in the pandemic?


“There is increasing evidence through comparisons of what’s happening in different countries and in different states, in terms of mask usage and mandates, that masks help slow transmission of COVID-19. Of course, it would be ideal if everyone had access to high-quality masks, but masks do not have to be 100% effective to reduce one’s exposure to virus. At this point, any reduction helps. I think it is becoming clear that the benefits to wearing face coverings outweigh any downsides.” (Posted July 8, 2020)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“At the beginning of the pandemic, the research community was unsure if the type of material used in a cloth mask mattered. And if so, is there an ideal material? To better understand these questions, we investigated 32 different fabrics made from 100% cotton, synthetics, and blends for both breathability and particle capture efficiency. On average, 100% cotton fabrics performed better than the synthetic or blends with the best cotton materials having some raised fibers, or nap. A simple way to test for nap is to feel it between your thumb and index finger, and if it feels fuzzy, like a baby’s blanket, that is a good sign. Synthetic materials, such as polyester, didn’t perform as well on average; 4 of the 5 worst performers were synthetic materials. This study also showed that it is possible to construct a multi-layered cloth mask that has the same or better particle capture than a surgical mask; for example, a 3-layer 100% cotton flannel mask. Using this information may guide people as they construct their own face coverings.” (Posted July 8, 2020)*

Chris Zangmeister, PhD
Research Scientist, National Institute of Standards and Technology (NIST)

“Face coverings can mitigate the transmission of SARS-CoV-2 by reducing the expulsion of droplets containing the virus. This fact has been known. Recent evidence suggests that infectious individuals may expel particles even smaller than droplets that contain the virus and may remain suspended in the air. Face coverings are less likely to disrupt this pathway of transmission.

“We analyzed smart device location data from before and after mask orders were implemented across the country and found that people spent more time outside their homes in response to mask orders. We interpret this finding as evidence that people perceived social interaction to be safer because mask-wearing was required. We highlight the need to continue emphasizing the importance of all protective behaviors, even when others are wearing face coverings. Our results should not be interpreted as a critique of mask orders, but rather as an indicator of the challenges of communicating public health messaging during a pandemic with rapidly evolving information.” (Posted July 8, 2020)*

Jude Bayham, PhD
Assistant Professor, Department of Agricultural and Resource Economics, Colorado State University

“Several recent studies have demonstrated that universal mask wear reduces the spread of COVID-19. The impact was somewhat surprising to me, as several other studies demonstrated the limited efficacy of cloth masks and because the growing body of evidence—including work in my own lab—suggests that human generated particles smaller than 5 µm (and likely much smaller) carry SARS-CoV-2. This must mean that the limited filtration offered by most cloth masks is sufficient to extend the time it takes to acquire an infection though aerosol inhalation if both infected and uninfected people wear them. This would likely limit transmission during casual contact of small numbers of people, but not necessarily prevent transmission during large gatherings—particularly indoors and where people are speaking loudly or singing, as has been highlighted by several events. Whatever mask you wear, it is still important that you wear it as effectively as possible. Touch it as infrequently as possible, particularly in the area where filtration is occurring. Furthermore, since masks are clearly not perfect, people should self-isolate if they are feeling ill or suspect that they have come into contact with someone who is infected.” (Posted July 8, 2020)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

* Links included in quotes were supplied by the expert.

April 9, 2020


What are the benefits of wearing a face mask, even if you are healthy?


“First, the surgeon’s mask is designed to prevent the wearer’s viral-laden aerosols spreading to others. The moisture droplets “impinge” upon the inner lining. When you inhale, most of the air is drawn from around the edges, so there is minimal protection of the wearer, but even so, there may be a little protection.

“The N95 mask is designed to protect the wearer from 95% of non-oil (N) dust particles above 0.3 micron (300 nm) size. Different viruses vary in size. The coronavirus is approximately 120 nm so two could fit side by side in the size of the holes in the mask; however, we are not trying to stop the free-floating virus but rather the water droplets that contain the virus, and those water droplets are much larger. So these masks can offer more protection, if they are properly sized and fitted, though they are still not 100%.” (Posted April 9, 2020)

Timothy Sly, PhD
Epidemiologist and Professor Emeritus, School of Public Health, Ryerson University, Toronto

“We now know that you can be infected with COVID-19 before you have symptoms, and you may not get any symptoms at all. Wearing a mask—the CDC is now calling it a cloth covering to distinguish it from medical masks used by healthcare workers—reduces the amount of virus you might spread into the air and onto surfaces if you happen to be sick. This would help slow transmission. A second benefit is that a mask, depending on the type of fabric, how tightly it fits, and how diligently you wear it, can help reduce your exposure to virus that might be present in the air, reducing your chances of catching the disease.” (Posted April 9, 2020)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“COVID-19 is considered to be spread mainly through droplets, while some aerosol transmission is likely too. Therefore, potential protective effects of face masks have attracted widespread attention.

“Our small scale study compared FFP2 (N95) masks, surgical masks and home-made masks (teacloth) worn by volunteers mimicking daily activities. We found that higher quality masks provided better protection, but that even improvised home-made masks contributed to protection against respiratory infections.

“This suggests that reduction of transmission in the population by population-wide deployment of face masks is plausible, which is also supported by some modelling studies. However, so far, this could not be unequivocally shown in real-life studies. Also, widespread use in China prior to the pandemic did not prevent rapid widespread transmission.

“Wearing a facemask could have additional positive effects, including:
• Less direct involuntary hand to mouth/nose contacts;
• Increased awareness, which may improve adherence to physical distancing;
• Can provide a feeling of empowerment; and
• Can reduce social stigmatization of mask wearing/face covering.” (Posted April 9, 2020)*

Joint statement by Peter Teunis, Visiting Biostatistician at Rollins School of Public Health, Emory University, Atlanta GA and Marianne AB van der Sande, MD, MPH, PhD, Head of the Department of Public Health, Professor of Public Health Epidemiology, Institute of Tropical Medicine, Antwerp, Belgium and Associate Professor of Epidemiology at Julius Global Health, UMCU, Utrecht, Netherlands

* Links included in quotes were supplied by the expert.


Are there risks associated with wearing a face mask?


“First, a false sense of security, arising from the sense that you are 100% protected. In fact, the 6ft (2 M) distancing is more important than the mask.

“Second, accidentally touching the face when you remove the mask. This can be very risky. Best to use sanitizer or alcohol spray, or handwashing before and after removing the mask.” (Posted April 9, 2020)

Timothy Sly, PhD
Epidemiologist and Professor Emeritus, School of Public Health, Ryerson University, Toronto

“There is some concern that people would touch their faces more if they are wearing a mask and thus possibly transmit viruses from their fingers to their eyes, nose, or mouth, but I am not aware of any evidence in support of this. There is also concern that wearing a face mask would provide a false sense of security, encouraging people to ease up on social distancing and handwashing. Hopefully, people who wear a mask are the cautious types anyway, who are doing everything they can to minimize the risk of transmission. I think some people have made a related argument about seat belts and risky driving behavior.” (Posted April 9, 2020)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“Wearing a facemask could have negative effects, including:
• Direct hand to mouth/nose contact can increase if adjusting mask, itching, etc.;
• May convey false sense of safety, which can reduce adherence to intensified handwashing and social distancing;
• Accumulated virus on mask surface may increase exposure when improperly handled or insufficiently cleaned; and
• Can lead to social stigmatisation.” (Posted April 9, 2020)

Joint statement by Peter Teunis, Visiting Biostatistician at Rollins School of Public Health, Emory University, Atlanta GA and Marianne AB van der Sande, MD, MPH, PhD, Head of the Department of Public Health, Professor of Public Health Epidemiology, Institute of Tropical Medicine, Antwerp, Belgium and Associate Professor of Epidemiology at Julius Global Health, UMCU, Utrecht, Netherlands Netherlands

“I think there are significant disadvantages to healthy people wearing a face mask; whether the advantages outweigh the disadvantages is up for debate. The general public is not trained to don, doff, or effectively wear respiratory protection and so they often perform these procedures incorrectly, which can cause increased risk. I have personally observed many untrained individuals wearing respiratory protection incorrectly, and in a way that offers limited or no protection. Further, if you believe that the mask is offering protection, then you must always consider it to be dirty and handle it in such a way that you don’t expose yourself while handling it. Finally, respiratory protection is uncomfortable and can cause people to adjust it frequently, which generally causes people to touch their face, increasing the risk for an exposure. Wearing a face mask should only be done with some training and understanding of the proper use, otherwise it offers little benefit.” (Posted April 9, 2020)

Joshua L. Santarpia, PhD
Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute

Are homemade masks helpful to slow the transmission of COVID-19?


“Initially, authorities in the West encouraged the public not to use masks, probably driven by the predicted shortage of masks for medical staff. This is changing now that we include the perspective that while the mask is not even close to 100% effective, in emergency situations even a small reduction of risk is better than no reduction.” (Posted April 9, 2020)

Timothy Sly, PhD
Epidemiologist and Professor Emeritus, School of Public Health, Ryerson University, Toronto

We don’t know for sure, but they could help and they can’t hurt. (Posted April 9, 2020)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

“Facemasks, in particular improvised ones, are relatively cheap and easy to deploy population-wide. They could therefore be particularly relevant for low- and middle-income countries (LMIC) where other personal protection is often unattainable, provided potential harms can be avoided.” (Posted April 9, 2020)

Joint statement by Peter Teunis, Visiting Biostatistician at Rollins School of Public Health, Emory University, Atlanta GA and Marianne AB van der Sande, MD, MPH, PhD, Head of the Department of Public Health, Professor of Public Health Epidemiology, Institute of Tropical Medicine, Antwerp, Belgium and Associate Professor of Epidemiology at Julius Global Health, UMCU, Utrecht, Netherlands

If people make masks at home, how should they do it?


“2-3 layers of 100% cotton on the inner side with a polyester outer weave. Much pleating to allow a large surface area once the mask is opened to cover nose, mouth and chin.” (Posted April 9, 2020)

Timothy Sly, PhD
Epidemiologist and Professor Emeritus, School of Public Health, Ryerson University, Toronto

“They should use a densely woven fabric, like a heavyweight t-shirt or dense kitchen towel, and make sure the mask fits well around the nose and mouth with no gaps.” (Posted April 9, 2020)

Linsey Marr, PhD
Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University

Creative Commons LicenseThis page is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. License applies to text and video only. Journalists are free to use any text or video on this page with or without attribution to SciLine.

Jude Bayham, PhD, Assistant Professor, Department of Agricultural and Resource Economics, Colorado State University

None

Loretta Fernandez, PhD, Associate Professor of Civil and Environmental Engineering and Marine and Environmental Sciences, Northeastern University, said:

“I have no conflicting interests to report.”

Laura Forsberg White, PhD, Associate Professor of Biostatistics, Boston University

None

Monica Gandhi, MD, MPH, Infectious Diseases doctor and Professor of Medicine, University of California, San Francisco

None

Rupali J. Limaye, PhD, Associate Scientist, Global Disease Epidemiology and Control, Johns Hopkins University

None

Linsey Marr, PhD Professor of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, said:

“Dr. Marr received a donation of masks from a US-based company. She has applied for funding to study the efficacy of homemade face coverings. Dr. Marr has provided expert advice on COVID-19 transmission, upon request, to the National Academies of Sciences, Engineering, and Medicine, World Health Organization, and other organizations.”

Joshua L. Santarpia, PhD, Associate Professor of Pathology and Microbiology at the University of Nebraska Medical Center and Research Director for Countering Weapons of Mass Destruction at the National Strategic Research Institute, said:

None

Asim Shah, MD, Professor of Community and Family Medicine, Professor of Psychiatry, Baylor College of Medicine

None

Dr. Timothy Sly, Epidemiologist and Professor Emeritus, School of Public Health, Ryerson University, Toronto, said:

“No interests financial or otherwise.”

Peter Teunis, Visiting Biostatistician at Rollins School of Public Health, Emory University, Atlanta GA and Marianne AB van der Sande, MD, MPH, PhD, Head of the Department of Public Health, Professor of Public Health Epidemiology, Institute of Tropical Medicine, Antwerp, Belgium and Associate Professor of Epidemiology at Julius Global Health, UMCU, Utrecht, Netherlands, said:

None

Yang Wang, PhD, Assistant Professor, Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, said:

“My laboratory is currently testing mask samples from a few US-based companies.”

Chris Zangmeister, PhD, Research Scientist, National Institute of Standards and Technology (NIST)

None