Masks have long been associated with infectious diseases. One need only recall the terrifying beaked masks that have become an iconic symbol of the Black Death of the 14th century, despite first emerging during the 17th century, when some doctors put them to use during the Plague of 1656. Thankfully, these macabre masks now only surface around Halloween. However, while they were based on the faulty principal of miasma theory, which postulates that the noxious smells associated with illness and death cause disease, they did provide its wearers with some protection against pathogens by minimizing direct contact, and the pleasant smelling herbs and flowers packed into the mask’s beak certainly made it easier to deal with the noxious smells of the day.
But what about today’s surgical, N95, and homemade face masks? Do they serve a purpose in protecting against the SARS-CoV-2 virus, which is causing havoc around the world? This has been an issue of hot debate. In the United States, the Centers for Disease Control and Prevention (CDC) initially advised against their use, and the US Surgeon General urged people to stop buying them, likely because hospitals and other healthcare institutions lacked sufficient access to personal protective equipment (PPE).1 The CDC has since changed its stance and has now advised the public to use cloth face masks when out in public, especially in areas of significant community-based transmission like grocery stores and pharmacies.2 The CDC notes that its change in recommendation stems from recent studies that show that people who lack symptoms can transmit the virus, and that just speaking and breathing can put large quantities of virus into the air and, subsequently, on surfaces.2 Therefore, the primary purpose of a face mask is not to protect the wearer but to protect the public at large in the event the wearer is infected, thereby curtailing transmissions and saving healthcare institutions from the burden those transmissions would have caused.
The question is, does the use of a mask really protect the public? There continue to be proponents on both sides of the issue, and even health organizations have not yet come to a consensus. The World Health Organization (WHO), for instance, still only advises the use of face masks for people caring for someone with COVID-19 or for people with respiratory symptoms, such as coughing or sneezing.3 The issue has also become highly politicized, and Vice President Mike Pence recently garnered significant criticism for not wearing one while visiting the Mayo Clinic, which led to much speculation over his actions.4 With so much contradictory information and actions by governmental bodies and medical professionals, it can be difficult to make sense of it all. So, what do the current data show? Let’s dive in.
Are Masks Effective in Preventing SARS-CoV-2 Transmission?
Much of the resistance against masks has centered around the argument that they do not help. As would be expected, the data regarding masks in the setting of SARS-CoV-2 and its associated disease, COVID-19, are still sparse. One small study examining the utility of masks in blocking SARS-CoV-2 was published on April 6, 2020 as a letter in the Annals of Internal Medicine, and it concluded “both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.”5 In the study, patients with SARS-CoV-2 were instructed to cough 5 times each onto a petri dish placed approximately 8 inches away from their mouths while wearing no mask, a surgical mask, a cotton mask, and then no mask again. In most cases, virus was detected on the petri dishes and outer surface of the masks. However, there are a few important points to consider:
- The study only included 4 patients. This is a very low-powered study, which means the study population is not sufficiently large to draw definitive conclusions.
- The study specifically examined the effect of coughing, which can expel air from the lungs at a speed of up to 100 miles per hour—this is the equivalent of a category 2 hurricane. Therefore, it is not surprising that significant volumes of the virus were detected on the outside of the masks and on the petri dish for many of the patients. However, current data suggest many people with SARS-CoV-2 are asymptomatic or have minimal symptoms, particularly early after infection and sometimes for up to 21 days,6 yet they are shedding large volumes of virus during this time just by speaking and breathing. One can surmise a mask may be better equipped to contain virus that is expelled less forcefully, and there are data to back this up. For example, a study published in Nature Medicine that examined exhaled breath samples of 246 people infected with at least 1 respiratory virus, whether a seasonal coronavirus (not SARS-CoV-2), rhinovirus, or influenza, concluded that surgical face masks could be useful in preventing transmission of these pathogens.7 Use of surgical face masks was found to reduce the detection of coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets.
Despite its limitations, the Annals of Internal Medicine study had two findings that may be particularly relevant to the general public. First, lower viral loads were observed in the petri dishes of all 4 patients after coughing with the cotton mask (2 layers, 100% cotton) versus coughing with the surgical mask (3 layers, polypropylene for all with polyethylene added to the inner layer). Since many people in the public are wearing homemade cloth masks, this provides reassurance that cloth masks can have benefit in reducing dissemination of the virus. Of course, other fabrics are also being used and some appear to be more protective than others—we’ll get to that in a bit. Second, and most importantly, all outer mask surfaces, whether surgical or cotton, had detectable viral loads, highlighting the importance of not touching the front of any mask that is worn. While it can be difficult to refrain from touching the mask to adjust it, doing so defeats its purpose and may facilitate the virus’s spread.
There are also observational data that support the use of face masks by the public. A study by microbiology and infectious disease specialists in Hong Kong, where face mask use by the general public is high (~96%), found significantly fewer cases of COVID-19 per million people compared with traditionally non-mask–wearing countries, including various European countries, the United States, Singapore, and South Korea.8 Among the COVID-19 clusters they identified in Hong Kong, 11 were in recreational, mask-off settings and only 3 were in workplace settings where masks were routinely worn. Based on their findings, the investigators concluded, “Community-wide mask wearing may contribute to the control of COVID-19 by reducing the amount of emission of infected saliva and respiratory droplets from individuals with subclinical or mild COVID-19.”8
Because the stakes with COVID-19 are so high, some healthcare experts have made a strong argument for applying the precautionary principle, which suggests “we should sometimes act without definitive evidence, just in case.”9 Some countries are already applying this principle by making use of facemasks in public a requirement. Austria, for example, widened its face mask requirement in parallel with loosening its lockdown.10 Time will tell how effective this measure is, but until there is a vaccine, use of such precautionary measures will be important, particularly as lockdowns are lifted.
Do Face Masks Cause Harm?
Some have argued against the use of face masks by indicating that they can cause harm. One claim made on social media is that they may increase the risk of heart attacks by reducing oxygen levels, but there does not appear to be any evidence to support this. Furthermore, a 2009 study suggests wearing a facemask in areas with high air pollution has beneficial cardiovascular effects, including on blood pressure and heart rate variability, by reducing exposure to particulates.11 This finding may be particularly relevant regarding COVID-19, as reports have shown that polluted areas in the United States, Italy, and China have been hardest hit by this disease.12-14 Although the reasons for this are multifactorial and include socioeconomic considerations, exposure to pollutants are known to increases the risk of respiratory and cardiovascular ailments, which have been associated with an increased risk of developing and dying from COVID-19.
Another concern with masks is that people are unlikely to wear them properly, which may prompt more frequent face touching as they try to adjust their masks. This may be a somewhat valid concern, particularly as many images and videos have surfaced highlighting this problem, including the extreme case of a Kentucky woman who cut a hole in the front of her face mask to make it easier to breathe.15 Clearly, most people know not to do this. And it seems enough people are doing a good enough job wearing masks for them to show a drastic impact on the infection numbers. For example, countries like Austria and the Czech Republic, which implemented mandatory use of face masks in public fairly early in the course of the pandemic, have had significant decreases in the spread of the virus.16 In the United States, states like New Jersey that have implemented compulsory use of face masks in grocery stores and other retail establishments, are also seeing the coronavirus curve flatten.17 Of course, other crucial measures, such as social distancing, have also greatly contributed.
Want to Make a Mask?
We’ve all heard about the N95 masks, which provide filtration efficiency against at least 95% of particles measuring >300 nanometers, including dust, mold, and various pathogens. These masks have been in short supply, which has prompted people to create their own cloth face masks. There has been debate over whether cloth masks are effective, but if constructed correctly, it appears they may be even more effective than N95 masks, particularly against particles that measure <300 nanometers, which is the range most viruses fall into.18 SARS-CoV-2 measures approximately 120 nanometers in diameter.19 Although it is larger than some viruses, it is still so small that you need an electron microscope to see it. Therefore, a mask needs to be able to filter out incredibly small particles to be effective against this tiny tyrant.
A study published in ACS Nano found that not all fabrics are created equal.18 When tested as a single layer, filtration efficiencies of commonly used fabrics, such as cotton, flannel, silk, and chiffon, ranged from 5% to 80% for particles measuring <300 nanometers and 5% to 95% for particles measuring >300 nanometers. The study investigators found filtration was significantly improved by using multiple layers of different fabrics, which is also in accordance with the CDC recommendations.20 Cotton hybrids combinations, such as cotton–silk, cotton–chiffon, and cotton–flannel, showed a filtration efficiency of >80% for particles <300 nanometers. Of these, a tightly woven cotton (600 thread count) paired with chiffon fabric made from polyester and spandex appeared to be the most effective, filtering out ≥97% of particles <300 nanometers. The investigators surmised this may be because this combination pairs the physical filtering of cotton with the electrostatic filtering of chiffon, providing a two-pronged approach.
Not sure if your cloth mask provides adequate filtration? You can consider adding a layer or two of facial tissue or paper towel to the inside of your mask. A report from Hong Kong found that kitchen paper towels have similar fabric size and gaps as the middle layer of a surgical mask. The report also suggests in the absence of a cloth mask, a combination of one sheet of tissue paper (inner layer) and two sheets of kitchen paper towel (middle and outer layers) could be used, with this combination achieving >90% of the filtration efficiency of surgical masks for particles measuring ≤200 nanometers.
While mask material is important, so is the fit of the mask. The study in ACS Nano showed that improper fit could reduce filtration efficiency by more than 60%.18 The CDC says the mask should fit snugly but comfortably against the side of the face.20 The wearer should also be able to breathe without restriction, but there should be no gaps.
Tutorials for sew and no-sew masks can be found at the CDC website.
- Wear a mask when out in public, especially when indoors or in crowded places.
- Once the mask is on your face, avoid touching it as much as possible, especially the front of the mask.
- Cloth masks should ideally be constructed of multiple layers of different types of fabrics for maximum filtration.
- The mask should cover the mouth and nose, fit snuggly against the sides of the face, and be free of gaps.
1. Feng S, Shen C, Xia N, Song W, Fan M, Cowling BJ. Rational use of face masks in the COVID-19 pandemic. Lancet Respir Med. 2020;S2213-2600(20)30134-X.
2. Centers for Disease Control and Prevention. Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission. Published April 3, 2020. Accessed May 2, 2020.
3. World Health Organization. Coronavirus disease (COVID-19) advice for the public: When and how to use masks. Accessed May 2, 2020.
4. Wise A. Leaving Off Mask At Mayo Clinic, Pence Said He Wanted To Look Workers ‘In The Eye’. Published April 28, 2020. Accessed May 2, 2020.
5. Bae S, Kim MC, Kim JY, et al. Effectiveness of surgical and cotton masks in blocking SARS-CoV-2: a controlled comparison in 4 patients. Published April 6, 2020. Accessed May 4, 2020.
6. Hu Z, Song C, Xu C, et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci. 2020;63(5):706-711.
7. Leung NH, Chi DKW, Shiu EYC, et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nature Medicine. Published April 3, 2020. Accessed May 4, 2020.
8. Cheng VC, Wong SC, Chuang VW, et al. The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. J Infect. 2020;S0163-4453(20)30235-8.
9. Greenhalgh T, Schmid MB, Czypionka T, Bassler D, Cruer L. Face masks for the public during the covid-19 crisis. BMJ. 2020;369.
10. Reuters. Austria widening face-mask requirement while loosening lockdown [news release]. Released April 6, 2020. Accessed May 5, 2020.
11. Langrish JP, Mills NL, Chan JK, et al. Beneficial cardiovascular effects of reducing exposure to particulate air pollution with a simple facemask. Part Fibre Toxicol. 2009;6:8.
12. Holden E, Lakhani N. Polluted US areas are among worst-hit by coronavirus – putting people of color even more at risk. The Guardian. Published April 14, 2020. Accessed May 6, 2020.
13. Conticini E, Frediani B, Caro D. Can atmospheric pollution be considered a co-factor in extremely high level of SARS-CoV-2 lethality in Northern Italy? Environ Pollut. 2020:114465.
14. Zhu Y, Xie J, Huang F, Cao L. Association between short-term exposure to air pollution and COVID-19 infection: evidence from China. Sci Total Environ. 2020;727:138704.
15. Toronto Sun. Kentucky woman cuts hole in face mask to breathe easier. Published May 5, 2020. Accessed May 6, 2020.
16. Dwyer C. In ‘Big Adjustment,’ Some European Countries Push For Residents To Wear Masks. Published April 1, 2020. Accessed May 8, 2020.
17. Sherman S. N.J. Virus Curve Flattens More; Murphy Says Not Ready to Reopen. Published April 25, 2020. Accessed May 8, 2020.
18. Konda A, Prakas A, Moss GA, et al. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS Nano.Published April 24, 2020. Accessed May 8, 2020.
19. Yu IM, Oldham ML, Zhang J, Chen J. Crystal Structure of the Severe Acute Respiratory Syndrome (SARS) Coronavirus Nucleocapsid Protein Dimerization Domain Reveals Evolutionary Linkage between Corona- and Arteriviridae*. J Biol Chem. 2006;281(25):17134-17139.
20. Centers for Disease Control and Prevention. Coronavirus Disease 2019. Cloth Face Covers. Reviewed April 13, 2020. Accessed May 8, 2020.
21. Hong Kong Consumer Council. Reuse Mask? DIY Mask? Published March 18, 2020. Accessed May 8, 2020.