Does Universal Mask Wearing Decrease or Increase the Spread of COVID-19?

Preface. The use and requirements of masks have become incredibly political and partisan. Unfortunately, far too much of science, knowledge, journalism, and even epistemology are becoming political.

The following is presented as is, for information only. — charles rotter


A survey of peer-reviewed studies shows that universal mask wearing (as opposed to wearing masks in specific settings) does not decrease the transmission of respiratory viruses from people wearing masks to people who are not wearing masks.

Further, indirect evidence and common sense suggest that universal mask wearing is likely to increase the spread of COVID-19.

This paper agrees that wearing masks in specific settings (such as healthcare facilities) achieves protective effects, although the masks should not be home-made, must be worn correctly, replaced frequently, and not overestimated.



Recently, the CDC has recommended universal mask wearing (UMW) in public settings. Some state governments have even issued orders mandating near-universal mask wearing. The recommendations apply to cloth mask, including disposable masks from non-woven materials, not surgical masks.

The UMW recommendation is expressed in (Brooks et al., “Universal Masking to Prevent SARS-CoV-2 Transmission—The Time Is Now,” 2020) co-authored by CDC Director Dr. Robert Redfield, and on the CDC website (CDC, “Coronavirus Disease 2019 (COVID-19),” 2020). The CDC website states:

“CDC recommends that people wear cloth face coverings in public settings and when around people who don’t live in your household… Cloth face coverings may help prevent people who have COVID-19 from spreading the virus to others. Cloth face coverings are most likely to reduce the spread of COVID-19 when they are widely used by people in public settings.

Cloth face coverings are recommended as a simple barrier to help prevent respiratory droplets from traveling into the air and onto other people when the person wearing the cloth face covering coughs, sneezes, talks, or raises their voice. This is called source control.”

Notice the expression “may help prevent.” This kind of expression is used in the marketing of echinacea and similar products, and it is effectively a non-statement alongside “may not help” or “may harm.” Unfortunately, “may help” is widely used as an affirmative recommendation for universal mask wearing.

When Masks are Useful

In many situations, wearing a face mask is certainly an effective source control measure. Mask wearing for infection source control is firmly established in some medical procedures. For example, surgeons wear surgical masks during procedures to protect patients’ open body cavities from infection via germs from the surgeon’s mouth and nose. Surgeons have to change their masks at least hourly and between patients[LG1]  (Kelsch, Changing Masks, 2010). Other professional examples include hairstylists, massage therapists, and nail technicians working with clients. Such uses are collectively referred to here as “Situation A.”

The next level of mask wearing includes patients waiting in clinics or undergoing certain procedures as well as people visiting nursing homes et cetera. The common feature of these situations is that people wear masks for short periods of time, with a clear purpose and sometimes under medical personnel’s supervision. This might be called “Situation A— “.

Some people might voluntarily wear masks in public settings to protect themselves and others. Such uses are referred to here as “Situation B.” On such uses, professional opinions differ. Some institutions (including the CDC and the US Surgeon General) say the benefits of Situation B mask wearing are uncertain and that harm may result from these uses because members of the general public might be unable to properly wear and handle masks.

Notice the differences between Situations A and B. When professionals (like surgeons) wear masks during a professional activity (like surgery), they:

  • Are trained and used to wearing masks.
  • Handle masks properly (including masks’ replacement, disposal, and disinfection).
  • Wear masks for a specific task and a short amount of time.
  • Use masks to protect against the forward spread of the germs. Surgical and cloth masks do not protect against germs spreading in other directions.

Members of the public, however, are likely not trained in proper mask wearing and handling—despite good intentions. A mask’s usefulness and potential dangers depend highly on the wearer’s actions.

When people are forced or even subtly encouraged to wear masks for long periods, they wear masks differently. Some people position their mask to cover only their mouth but not their nostrils, though nostrils have higher viral concentration, see Leung et al. below. Some people frequently remove and replace their masks. When removing their masks, some people fold or roll masks so that the interior and exterior sides come into contact. Some people drop their masks into a purse, pocket, or glove box only to use them again at their next stop. After a few cycles, the masks’ interior and exterior become interchangeable. Even if a wearer has no infection, their mask can pick up coronavirus and other germs from the air and from dust particles. These masks can then spread the virus because every time the wearer exhales, the coronavirus and any other germs that have accumulated in the mask spread into the air. This kind of masking wearing is referred to here as “Situation C.”

When people are told to wear masks in specific situations to protect vulnerable individuals—for example, in pharmacies, nursing homes, and medical buildings—most people are careful to follow rules and recommendations. However, when people are ordered to wear masks everywhere and all the time, proper mask use and handling become significantly less probable. It is possible to enforce mask wearing, but it is impossible to enforce proper mask handling.

Mask Effects

The coronavirus spreads via droplets and aerosols that are exhaled by contagious persons with or without symptoms. Technically, it is also transmitted by fomites, but fomites originate in exhaled droplets and aerosols. In the best-case scenario, a cloth mask catches large droplets and some of the forward-moving aerosol. Neither surgical nor cloth mask restrains aerosols from escaping at the sides, top, and bottom of the mask.

Masks redirect aerosol flow to all sides. Though we take protective measures, none of these measures protect against viral-loaded aerosols—especially when they can settle downward from above. For example, we know not to sneeze or cough in other people’s direction. And recently, we have also become accustomed to keeping six feet of distance away from others in a frontal arc. Moreover, clerks, cashiers, and other service providers are usually protected by plexiglass barriers. But because these measures fail to protect against viral-loaded aerosols, even ideally worn and cared-for masks might cause more harm than benefits.

Additional Downsides of Wearing a Mask during the COVID-19 Outbreak

All masks make breathing more difficult, requiring more effort to inhale and exhale and potentially causing more viral load to be expelled into the air. Moreover, when a non-contagious person wears a cloth mask, his or her mask accumulates the coronavirus and other germs from the environment. If a contagious person wears a cloth mask, the mask also accumulates some viral load with each breath, and soon, it might discharge more viral load with each exhalation than the contagious person would otherwise exhale—and in more directions.

Masks cause heavier, deeper, and more forceful breathing as well as straining—all of the attributes believed to have caused exceptionally bad outcomes in the case of a church choir in Seattle (Read, “A choir decided to go ahead with rehearsal. Now dozens of members have COVID-19 and two are dead,” 2020). Deeper breathing allows the coronavirus to go deeper into the lungs, causing infection to take hold faster. The article explains:

“Jamie Lloyd-Smith, a UCLA infectious disease researcher, said it’s possible that the forceful breathing action of singing dispersed viral particles in the church room that were widely inhaled.”

As of now, hundreds of thousands of people are breathing similarly forcefully through masks in public spaces, and other people are inhaling what mask wearers expel. Read’s article contains another illustrative passage:

“Linsey Marr, an environmental engineer at Virginia Tech and an expert on airborne transmission of viruses, said some people happen to be especially good at exhaling fine material, producing 1,000 times more than others.”

This finding had been described in an unrelated study (Edwards et al., Inhaling to mitigate exhaled bioaerosols, 2004).

The Math of Viruses and Cases

The idea that cloth masks can significantly decrease transmission of the coronavirus faces a mathematical challenge. Viral load, or titer, is usually expressed as log10 of the number of viruses per unit of volume, and it is the best unit for estimating a virus’s ability to infect people. On the log10 scale, an emission decrease like 40% hardly registers. The same is true of a 60% increase. Unfortunately, masks can cause much higher emissions. A virus-contaminated mask worn by a healthy person, shedding viruses during breathing, would increase the viral load in a room from 0 to a non-zero level that may be sufficient to infect another person.

Literature Review

Unsurprisingly, academic literature shows an absence of benefits for universal mask wearing as source control and does not address the possible harms.

(Xiao et al., Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare SettingsPersonal Protective and Environmental Measures,May 2020) is the only systematic revie[LG2] w focusing on whether face masks decrease the transmission of viral respiratory disease in a nonhealthcare setting. With a focus on source control, the authors find that masks cannot decrease transmission in this context—or, at least, cannot have a significant effect—and that masks might even increase transmission. There is no reason to believe the results for COVID-19 differ from the results for influenza.

(Martin,” Response to Greenhalgh et al.,”2020) deserves to be quoted here:

“First, the evidence for the effectiveness of face masks in reducing viral transmission is very weak. Few studies examine the use of face masks in community settings; those that do find no evidence of reduced transmission compared with no face masks. Absence of evidence is not evidence of absence: both recent systematic reviews cautiously suggest that in some circumstances, wearing of face masks may be warranted. They also note, however, the absence of systematic study of harms.”

 (MacIntyre et al., “A cluster randomised trial of cloth masks compared with medical masks in healthcare workers,” 2015) is not directly relevant here because they investigate mask wearing for wearers’ protection. Nevertheless, they find that for healthcare workers, wearing cloth masks is worse than not wearing any masks. Wearing surgical masks was beneficial in the study.

References on the CDC website and in Brooks et al.

This subsection covers all the references in the CDC recommendations and Brooks et al. (the CDC team). Many sources address asymptomatic and aerosol transmission of the Wuhan coronavirus, which are not in doubt anymore, so they are left out here. The rest of the sources include some anecdotal cases, examples of lab-tested masks or mask fabrics, and studies showing masks’ effectiveness in hospital settings, followed by attempts to extrapolate these results for universal mask wearing. Many studies, or their interpretations, combine multiple fallacies.

Healthcare workers and patients wearing masks in hospital undoubtedly decreases virus transmission. However, this effect cannot be generalized to make a case for universal mask wearing. But (Wang et al., “Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers,” 2020) miss an elephant in the room. The drop in new infections started before their implementation of masks, probably because healthcare workers started taking hydroxychloroquine for prophylaxis See(Goldstein, “JAMA Rejected my Comment on Masks and HCQ,”2020). The effectiveness of COVID-19 prevention among healthcare workers via hydroxychloroquine prophylaxis is also shown in (Chatterjee et al., “Healthcare workers & SARS-CoV-2 infection in India,” 2020). It is unfortunate that Brooks et al. (the CDC team including CDC Director Dr. Redfield) selected this irrelevant and erroneous study as a cornerstone for their article.

(Schwartz et al., “Lack of COVID-19 transmission on an international flight,” 2020)

provides anecdotal evidence. Worse still, its evidence is probably incorrect. It describes a COVID-19 patient wearing a mask on a January 22 flight. After the flight, six passengers became sick[LG3]  with COVID-19 symptoms. They tested negatively, probably because of high ratio of false positives in the tests at that time.

(Hendrix, “Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy — Springfield, Missouri,” May 2020)

provides similarly anecdotal evidence on the absence of coronavirus transmission from the two stylists described in the study, at least one of whom was capable of transmission, to their clients. The stylists wore masks, so this case constitutes Situation A. The stylists’ clients wore masks, too.

(National Academies of Sciences, “Rapid Expert Consultation on the Possibility of Bioaerosol Spread of SARS-CoV-2 for the COVID-19 Pandemic (April 1, 2020),” 2020)

confirms that the coronavirus can spread via aerosols [LG4] generated by a person’s exhalation. They also state, “These findings suggest that surgical face masks [not cloth masks —LG] could reduce the transmission of human coronavirus and influenza infections if worn by infected individuals capable of transmitting the infection.” Even this limited suggestion, pertaining only to surgical masks, is based solely on Leung et al., discussed below.

(Leung et al., “Respiratory virus shedding in exhaled breath and efficacy of face masks,” 2020)

examines the exhalation of patients with any of three types of virus (flu, coronavirus, and rhinovirus) collected over 30-minute intervals with no forced cough. The researches attempted to collect some, but not all, sideways flow. This semi-realistic testing demonstrated a lower effectiveness for even surgical masks. Detection of the virus was:

  • In droplets, masks versus no masks: 11% versus 21%.
  • In aerosols, masks versus no masks: 26% versus 46%.

The surprising aspect of Leung et al.’s study is surgical masks’ apparent low effectiveness in blocking virus-laden droplets. Droplets are supposed to hit masks, even as aerosols escape along the mask’s four sides, and remain inside the mask. Surgical masks retain over 99% of the exhaled droplets that hit them. Only 17 persons were infected by coronaviruses, none of which were the COVID-19 pathogen. Leung et al. also finds: “On average, viral shedding was higher in nasal swabs than in throat swabs”

(Johnson et al., “A Quantitative Assessment of the Efficacy of Surgical and N95 Masks to Filter Influenza Virus in Patients with Acute Influenza Infection,” 2009)

confirms that surgical masks significantly reduced the forward flow of the virus when flu patients coughed into a testing device. The authors stressed that participants wore masks for only for three to five minutes and that side flow was not collected.

(Konda et al., “Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks,”2020)

found that surgical mask material [LG5] intercepts about 99% of droplets and large (>300 nm) aerosol particles. But in tests were holes were made that had an area of only 1%, the effectiveness dropped by 60%! Cotton and other common materials have lower filtration effectiveness, although cotton quilt and high-TPI cotton are quite effective, and using multiple layers further increases effectiveness to nearly 99%. But the gaps in masks are much larger than 10%, so only large droplets expelled forward are captured. The CDC does not claim otherwise. Also, that finding suggests that an individual who needs to wear a mask should neither try to use a homemade mask nor use a surgical mask for COVID-19.

(Ma et al., “Potential utilities of mask-wearing and instant hand hygiene for fighting SARS-CoV-2,” 2020)

has an inaccurate title. The study tests mask fabrics’ filtering ability, not actual masks worn by real persons.

(Aydin et al., “Performance of Fabrics for Home-Made Masks Against the Spread of Respiratory Infections Through Droplets,”2020)

is another study of fabrics. They also explain why a mask may stop large droplets but allow small droplets and aerosols to escape: “when an infected individual coughs, sneezes, or talks into a mask, the droplets that would hit the inside of the mask are relatively large, and have high momentum.”

(Davies et al., “Testing the Efficacy of Homemade Masks,2013)

is a study of an unusual type of mask:tightly fit (like a respirator) homemade masks. As expected, these masks decreased the number of exhaled germs, but nobody recommends or uses tightly fit masks for COVID-19.

(Anfinrud et al., “Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering,” 2020)

visualizes droplets motion, consistently with the belief that large forward moving droplets are intercepted by a mask.

(Hatzius, “Goldman Sachs | Insights – Face Masks and GDP,”2020)

is not a scientific paper, one passage merits attention here:

By our estimates, the increase in distancing our Effective Lockdown Index (ELI)—a combination of official restrictions and actual social data—subtracted 17% from US GDP between January and April, and other countries with even more aggressive restrictions saw even larger economic effects.”

(Greenhalgh, “Face coverings for the public,” 2020)

 study’s declared methodis narrative rebuttal. Accordingly, it reports no scientific findings.

(Fisher, “Factors Associated with Cloth Face Covering Use Among Adults During the COVID-19 Pandemic — United States,” April and May 2020)

, published on the CDC website on July 14, reports statistics on how many people wore masks. These statistics are irrelevant to the question of whether masks were useful or harmful.


  1. Anfinrud, Philip; Stadnytskyi, Valentyn; Bax, Christina E.; Bax, Adriaan: Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering, in: New England Journal of Medicine, 2020, vol. 382, no. 21, pp. 2061–2063, available at:, accessed: 07/23/2020.
  2. Aydin, Onur; Emon, Md Abul Bashar; Cheng, Shyuan; Hong, Liu; Chamorro, Leonardo P.; Saif, M. Taher A.: Performance of Fabrics for Home-Made Masks Against the Spread of Respiratory Infections Through Droplets: A Quantitative Mechanistic Study, in: medRxiv, 2020.04.19.20071779, available at:, accessed: 07/22/2020.
  3. Brooks, John T.; Butler, Jay C.; Redfield, Robert R.: Universal Masking to Prevent SARS-CoV-2 Transmission—The Time Is Now, in: JAMA, 2020, available at:, accessed: 07/23/2020.
  4. CDC: Coronavirus Disease 2019 (COVID-19), in: Centers for Disease Control and Prevention, 2020, available at:, accessed: 07/23/2020.
  5. Chatterjee, Pranab; Anand, Tanu; Singh, Kh Jitenkumar; Rasaily, Reeta; Singh, Ravinder; Das, Santasabuj; Singh, Harpreet; Praharaj, Ira; Gangakhedkar, Raman R.; Bhargava, Balram; Panda, Samiran: Healthcare workers & SARS-CoV-2 infection in India: A case-control investigation in the time of COVID-19, in: Indian Journal of Medical Research, 2020, vol. 151, no. 5, p. 459, available at:;year=2020;volume=151;issue=5;spage=459;epage=467;aulast=Chatterjee;type=0, accessed: 07/22/2020.
  6. Davies, Anna; Thompson, Katy-Anne; Giri, Karthika; Kafatos, George; Walker, Jimmy; Bennett, Allan: Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?, in: Disaster Medicine and Public Health Preparedness, 2013, vol. 7, no. 4, pp. 413–418, available at:, accessed: 07/22/2020.
  7. Edwards, David A.; Man, Jonathan C.; Brand, Peter; Katstra, Jeffrey P.; Sommerer, K.; Stone, Howard A.; Nardell, Edward; Scheuch: Inhaling to mitigate exhaled bioaerosols, in: Proceedings of the National Academy of Sciences of the United States of America,2004,  vol. 101, no. 50, p. 17383, available at:
  8. Fisher, Kiva A.: Factors Associated with Cloth Face Covering Use Among Adults During the COVID-19 Pandemic — United States, April and May 2020, in: MMWR. Morbidity and Mortality Weekly Report, vol. 69, available at:, accessed: 07/23/2020.
  9. Goldstein, Leo: JAMA Rejected my Comment on Masks and HCQ, available at:, accessed: 07/23/2020.
  10. Greenhalgh, Trisha: Face coverings for the public: Laying straw men to rest, in: Journal of Evaluation in Clinical Practice, 2020, available at:, accessed: 07/23/2020.
  11. Hatzius, Jan: Goldman Sachs | Insights – Face Masks and GDP, in: Goldman Sachs, 2020, available at:, accessed: 07/22/2020.
  12. Hendrix, M. Joshua: Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy — Springfield, Missouri, May 2020, in: MMWR. Morbidity and Mortality Weekly Report, vol. 69, available at:, accessed: 07/22/2020.
  13. Johnson, D.F.; Druce, J.D.; Birch, C.; Grayson, M.L.: A Quantitative Assessment of the Efficacy of Surgical and N95 Masks to Filter Influenza Virus in Patients with Acute Influenza Infection, in: Clinical Infectious Diseases, 2009, vol. 49, no. 2, pp. 275–277, available at:, accessed: 07/22/2020.
  14. Kelsch, Noel: Changing masks, in: Registered Dental Hygienist (RDH) Magazine, 2010, available at:, accessed: 07/22/2020.
  15. Konda, Abhiteja; Prakash, Abhinav; Moss, Gregory A.; Schmoldt, Michael; Grant, Gregory D.; Guha, Supratik: Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks, in: ACS nano, 2020, vol. 14, no. 5, pp. 6339–6347,
  16. Leung, Nancy H.L.; Chu, Daniel K.W.; Shiu, Eunice Y.C.; Chan, Kwok-Hung; McDevitt, James J.; Hau, Benien J.P.; Yen, Hui-Ling; Li, Yuguo; Ip, Dennis K.M.; Peiris, J.S. Malik; Seto, Wing-Hong; Leung, Gabriel M.; Milton, Donald K.; Cowling, Benjamin J.: Respiratory virus shedding in exhaled breath and efficacy of face masks, in: Nature Medicine, 2020, vol. 26, no. 5, pp. 676–680,
  17. Ma, Qing-Xia; Shan, Hu; Zhang, Hong-Liang; Li, Gui-Mei; Yang, Rui-Mei; Chen, Ji-Ming: Potential utilities of mask-wearing and instant hand hygiene for fighting SARS-CoV-2, in: Journal of Medical Virology, 2020 available at:, accessed: 07/23/2020.
  18. MacIntyre, C. Raina; Seale, Holly; Dung, Tham Chi; Hien, Nguyen Tran; Nga, Phan Thi; Chughtai, Abrar Ahmad; Rahman, Bayzidur; Dwyer, Dominic E.; Wang, Quanyi: A cluster randomised trial of cloth masks compared with medical masks in healthcare workers, in: BMJ Open, 2015, vol. 5, no. 4, p. e006577, available at:
  19. Martin, Graham: Response to Greenhalgh et al.: Face masks, the precautionary principle, and evidence-informed policy, 2020, available at:, accessed: 07/22/2020.
  20. National Academies of Sciences, Engineering, and Medicine: Rapid Expert Consultation on the Possibility of Bioaerosol Spread of SARS-CoV-2 for the COVID-19 Pandemic (April 1, 2020), Washington, DC: The National Academies Press, available at:
  21. Richard Read: A choir decided to go ahead with rehearsal. Now dozens of members have COVID-19 and two are dead, in: Los Angeles Times, 2020, available at:, accessed: 07/22/2020.
  22. Schwartz, Kevin L.; Murti, Michelle; Finkelstein, Michael; Leis, Jerome A.; Fitzgerald-Husek, Alanna; Bourns, Laura; Meghani, Hamidah; Saunders, Andrea; Allen, Vanessa; Yaffe, Barbara: Lack of COVID-19 transmission on an international flight, in: Canadian Medical Association Journal, 2020, vol. 192, no. 15, p. E410, available at:
  23. Wang, Xiaowen; Ferro, Enrico G.; Zhou, Guohai; Hashimoto, Dean; Bhatt, Deepak L.: Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers, in: JAMA, 2020, available at:, accessed: 07/25/2020.
  24. Xiao, Jingyi; Shiu, Eunice Y.C.; Gao, Huizhi; Wong, Jessica Y.; Fong, Min W.; Ryu, Sukhyun; Cowling, Benjamin J.: Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures – Volume 26, Number 5—May 2020 – Emerging Infectious Diseases journal – CDC, available at:, accessed: 07/22/2020.

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July 25, 2020 at 08:59PM

2 thoughts on “Does Universal Mask Wearing Decrease or Increase the Spread of COVID-19?”

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