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

By Leo Goldstein.- Re-Blogged From WUWT


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,


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