Last updated by The POOG on September 13, 2020.

The topic of masks is one on which not much research could be found. Without solid studies to support policy, governments end up relying on ‘experts’ and the results to date have been notoriously unreliable, with positions changing sides like a puck in a hockey game.

In order to evaluate the efficacy of masks, we need to understand what they are being used for. We will first discuss the modes of COVID-19 transmission. Then we will be able to address such questions as design and materials. Finally, we then assess their efficacy.

Modes of Disease Transmission

Surface contact is well understood as a form of transmission. The length of time the virus can persist in a viable form on various surfaces has been well studied. The resulting commendation is to wash your hands frequently in a prescribed manner and use hand sanitizers.

The other form of transmission is airborne and this is broken down into two categories, droplets and bio-aerosols. An extensive industry study[10] of the the two by Production Automation Corporation (PAC) gives the reader background on the two classes of airborne transmission. In particular, it reviews the literature on bio-aerosols. As well, consider an article by Mackay (2020)[11] and Debczak (2020)[14].

A study[13] by the CNFU reviewed 4 dozen articlesa and papers.

A NASEM Rapid Expert Consultation[5] discusses both forms of airborne transmission in the context of cloth masks worn to protect the public from the wearer.

Droplet Transmission

When you cough or sneeze, the force of the action can cause one to expel droplets of water or mucous. On one end of the spectrum, they are large enough to be visible and felt. On the other end, they may not be visible but can still be filtered out by some materials.

The droplet’s size has two important considerations. Each droplet is large enough to carry a heavy viral load. On the other hand, due to their size (and weight), they do not travel far due to gravity. The two metre rule is a heuristic for protection from coughing and sneezing.

Aerosol Transmission

Aerosols are formed by normal exhalation of fine droplets not visible to the naked eye. If you breath closely on a window, it will fog up due to the fine fine droplets of moisture that you normally exhale. In an infected person, these very small droplets can carry virus particles.

As mentioned above, the PAC paper[10] reviews several studies that support aerosol transmission of COVID-19.

Justin Morgenstern did a large survey of the literature on aerosols and disease transmission.

Due to the particle size, they remain in the air longer, especially if there are air currents that they are floating on. The implication of this is that they travel considerably farther than the larger droplets. Because they remain airborne longer, they can build up a concentration in closed spaces such as buses, trains and subways. Prolonged exposure in such an environment can give one a heavy viral load.

The nature and behaviour of aerosols is dependent on many factors related to the virus, human physiologic, droplet size, and the environment, making studies and remedial strategies complex.

Types of Masks

Disposable medical masks (surgical masks) are loose-fitting devices that were designed to be worn by medical personnel to protect accidental contamination of patient wounds, and to protect the wearer against splashes or sprays of bodily fluids.

Respirators such as N-95 and P2 masks are tight-fitting masks that can protect the wearer from fine particles, providing better protection against virus exposures when properly worn. An article by Eric Litke[12], explains about N-95 mask effective filtration:

N95 masks actually have that name because they are 95% efficient at stopping particles in their least efficient particle size range — in this case those around 0.3 microns.

Litke (2020)

They are actually more effective at stopping particles smaller than 0.3 microns.

A third type of mask is the reusable cloth mask used in the community, rather than disposable medical masks, because of cost and availability. Studies of their efficacy were hard to find and only in comparison with other mask types. We did find a filtration study[16] that showed a wide range of aerosol filtering ability based on design and materials. It should be noted that this only indicates filtering efficiency and not aerosol protection which is also highly dependent on fit and mask maintenance.

Discussion of Results of Studies Cited

Xiao et al. (2020) reviewed the evidence from 14 randomized controlled trials of standard non-pharmaceutical personal protective measures and environmental hygiene measures in non-healthcare settings. This included hand washing and the use of masks. Their results are:

We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility.

Xiao et al. (2020)[1]

MacIntyre et al. (2015) compared cloth masks to medical masks. cloth masks and found that:

Penetration of cloth masks by particles was almost 97% and medical masks 44%.

Cloth masks resulted in significantly higher rates of infection than medical masks, and also performed worse than the control arm [of the study].

MacIntyre et al. (2015)[2]

Another study by MacIntyre et al. (2011)[3] compared the efficiency of N-95 masks, both fit-tested and non-fit-tested to surgical masks. They found no significant difference between the two N-95 groups which suggests that arguments against the use of N-95 masks by the public due to fitting issues are bogus. They found that:

infection were consistently lower for the N95 group compared to medical masks. … There was no significant difference in outcomes between the N95 arms with and without fit testing.

MacIntyre et al. (2011)[3]

Brosseau, and Sietsema (2020)[4] (also MacIntyre et al. (2015)[8]), surveyed the publish literature on cloth masks, noted its scarcity, but stated:

We do, however, have data from laboratory studies that indicate cloth masks or face coverings offer very low filter collection efficiency for the smaller inhalable particles we believe are largely responsible for transmission

Brosseau, and Sietsema (2020)[4]

Quesnel (1975) tested 5 types of surgical masks and found that:

the gross efficiency of all the masks was high, but that some masks were distinctly better at small particle “filtration” than others.

Quesnel (1975)

Yang et al. (2011)[6], in a study of health care workers in small and large hospitals found “the protective efficacy of medical masks is better than that of cotton yarn ones“.

Virtue Signalling and Shaming

We’ve gone through cycles where the same authorities have told us that “masks don’t work”, then “masks work”. Very recently the narrative around masks has bifurcated to “masks don’t protect you from others” but “masks protect others from you”. Or in other words, “I must wear a mask so that I can’t give you what I don’t have”.

Apart from sounding like a strategy invented in the boardroom of a Wall Street advertising firm, it doesn’t hold up to scrutiny.

The National Academies of Sciences, Engineering, and Medicine (NASEM) was recently instructed to do a Rapid Expert Consultation with the objective:

The aim of this rapid expert consultation is to respond to your request concerning the effectiveness of homemade fabric masks worn by the general public to protect others, as distinct from protecting the wearer.

… in terms of their ability to reduce viral spread during the asymptomatic or presymptomatic period.

Besser et al. (2020)[5]

Someone was in a hurry to find ‘scientific’ evidence to support the new narrative. The authors note that:

in addition to being spread by respiratory droplets that one can see and feel, SARS-CoV-2 can also be spread by invisible droplets, as small as 5 microns (or micrometers), and by even smaller bioaerosol particles.


The NASEM finding from a review of studies in the literature, concluded that the “current level of benefit, if any, is not possible to assess.” The studies generally tested filtration properties of various materials.

Of specific studies and findings, one noted that “both homemade and surgical masks reduced the number of large-sized microorganisms expelled” while another noted that “N95 masks provided 25 times the
protection of surgical masks and 50 times the protection of cloth masks

Negative Impact of Mask Use

There are a few reports hypothesizing negative health risks from using masks. The most common one is the buildup of bacteria or virus pathogens on or in the mask that may then be re-transmitted by touching or breathing[17].


Studies on the use of masks and respirators in clinical and community settings are few, particularly given the number of variables such as materials, fit, and diseases to be protected from. There are some laboratory studies of filtration by different materials and mask types.

In general, N-95 masks offer better protection over medical or surgical masks (25 times) and cloth masks (50 times). Fit testing of N-95 masks offers no additional advantage, nullifying the argument against their use by the general public that the latter can’t fit them properly if simple directions are followed.

Medical masks offer a degree of protection for droplet and fluid transmission but little protection from aerosols. A 1975 study of 5 types which showed a wide range of effectiveness has hopefully informed an optimal standard for production. These conclusions are born out by the extensive CFNU study[13].

Cloth masks, based on the limited testing available, have shown to be largely ineffective, particularly given the lack of manufacturing standards. As the NASEM report notes, overall, cloth masks offer some reduction in the number of large-sized particles expelled but little efficacy for stopping aerosols.

There are, however, some advocates of universal masking over the use of social distancing, for both source control and general protection[15].

Finally, NASEM states that the current level of benefit [of cloth masks], if any, is not possible to assess. This means that there is no scientific basis for the current virtue signalling policy of cloth mask use. Overall, they are only marginally effective in preventing disease spread.


  1. Xiao, J., Shiu, E., Gao, H., et al. (2020). Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures. Emerging Infectious Diseases, 26(5), 967-975.
  2. MacIntyre, C.R., Seale, H., Dung, T.C., et al. (2015). A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015; 5(4): e006577. Published online 2015 Apr 22. doi: 10.1136/bmjopen-2014-006577.
  3. MacIntyre, C.R., Wang, Q., Cauchemez, S., et al. (2011). A cluster randomized clinical trial comparing fit‐tested and non‐fit‐tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza. 2011 May; 5(3): 170–179. Published online 2011 Jan 27. doi: 10.1111/j.1750-2659.2011.00198.x
  4. Lisa M Brosseau, and Margaret Sietsema, (2020). COMMENTARY: Masks-for-all for COVID-19 not based on sound data. CIDRAP. Apr 01, 2020.
  5. Besser, R., Fischhoff, B., Jayaraman, S., and Osterholm, M. (2020) Rapid Expert Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic. National Academies of Sciences, Engineering, and Medicine (NASEM), April 8, 2020, Washington, DC:; PDF.
  6. Peng Yang , Holly Seale, C Raina MacIntyre, et al. (2011). Mask-wearing and respiratory infection in healthcare workers in Beijing, China. Braz J Infect Dis. Mar-Apr 2011;15(2):102-8. doi: 10.1016/S1413-8670(11)70153-2.
  7. Quesnel, L.B. (1975). The efficiency of surgical masks of varying design and composition. Br J Surg. 1975 Dec;62(12):936-40. doi: 10.1002/bjs.1800621203.
  8. MacIntyre, C.R. and Chughtai, A.A., (2015). Facemasks for the prevention of infection in healthcare and community settings. BMJ. 2015 Apr 9;350:h694. doi: 10.1136/bmj.h694.
  9. Morgenstern, J. Aerosols, Droplets, and Airborne Spread: Everything you could possibly want to know. Published -Updated .
  10. Droplets vs Airborne – Science of Airborne Droplets, Aerosols, Particles, and Face Masks. Production Automation Corporation, July 2020.
  11. Like, E. Fact check: No, N95 filters are not too large to stop COVID-19 particles. USA TODAY, June 11, 2020.
  12. CFNU research summary on COVID-19. Canadian Federation of Nurses Unions, updated August 4, 2020.
  13. Debczak, M. Airborne vs. Aerosol vs. Droplet: What’s the Difference? MF, April 14, 2020.
  14. Susanna Esposito, Nicola Principi, Chi Chi Leung. Universal use of face masks for success against COVID-19: evidence and implications for prevention policies. European Respiratory Journal 2020 55: 2001260; DOI: 10.1183/13993003.01260-2020.
  15. Abhiteja Konda, Abhinav Prakash, Gregory A Moss, et al. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano. 2020 May 26;14(5):6339-6347. doi: 10.1021/acsnano.0c03252.
  16. Russell Blaylock. Blaylock: Face Masks Pose Serious Risks To The Healthy. Technocracy News and Trends, May 11, 2020.