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Mask Science: Proving a Negative


Philip Buckler



Philip is a General Dentist (DDS). He graduated from the University of Detroit Mercy School of Dentistry in 2010. He is currently on activy duty in the Army, however he is doing appearances only as a civilian.

Contrary to popular slogans, it is entirely possible to prove a negative. We do so all the time in our day-to-day lives. The Scientific Method entails proving negatives. This has particular relevance when we ask: “Does mask use mitigate respiratory viral spread?” and the even bigger question: “Are mask mandates morally justified?”


Any multiple choice test strategy guide worth reading will tell you that, when unsure what the right answer is, you should use a strategy of elimination – ruling out wrong answers to help you determine the final right answer. Likewise, science progresses most often by eliminating incorrect possibilities one at a time. Proving negatives is integral to the scientific method.  


Sometimes you can prove a negative simply by showing that the concept is logically contradictory, such as in the case of a triangle with four sides or a married bachelor – such things cannot exist because their definition is a self-contradictory absurdity. Empirically, you more often prove a negative by surveying the area where you would expect to find evidence if your hypothesis were true. If you do not find evidence where your hypothesis predicts it should be, then that lack of findings actually constitutes positive evidence the hypothesis is false.


In the case of masks, if it were true that masks are effective at mitigating the spread of respiratory viral infections, we should see a statistically-significant difference in respiratory viral transmission rates when we compare masked and non-masked study participants – particularly in randomized controlled trials. A substantial statistically-significant difference in viral infection rates when masks are used is a necessary but not sufficient precondition to morally justify mask mandates in the name of COVID-19.


Similarly, if it were true that our use of masks provides protection for others, we should expect to see a statistically-significant difference in post-operative microbial infection rates when various medical procedures are conducted with masked or non-masked medical personnel.


If the theory underlying the use of facemasks were accurate, we should also expect multiple randomized controlled trials to show a statistically-significant difference in rates of respiratory viral infection between users of basic medical masks and N95 masks.


The randomized controlled trials conducted over the last three decades with thousands of participants, examining the protective effects of facemasks have consistently found no statistically-significant differences in:

·        respiratory viral transmission between masked and non-masked study cohorts; [1-11]

·        respiratory viral transmission between medical mask and N95 mask-users; [12-15]

·        post-operative infection rates when the healthcare providers are masked or un-masked [16, 17]


This is not simply a lack of evidence that masks work. This is a repeated pattern of positive evidence that masks do not work, and it is cumulatively far stronger than the the whole body of evidence from 2020 and 2021 which has been adduced in an attempt to justify mask mandates. Furthermore, this is not even taking into account the many observational studies, laboratory studies, meta-analyses, and systematic reviews from the last 30 years which have also found this same lack of efficacy regarding masks.


If masks were effective, this abundance of negative findings and dearth of positive findings would be the reverse of what we actually observe. The evidence supporting facemask use is not enough to surmount even the empirical hurdles, much less the moral ones, necessary to justify compulsory masking.


Mandatory masking is the wrong answer when looking at multiple choices in public health policy.




·                  1.            Bundgaard, H., et al., Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers : A Randomized Controlled Trial. Ann Intern Med, 2021. 174(3): p. 335-343.

·                  2.            MacIntyre, C.R., et al., 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 Other Respir Viruses, 2011. 5(3): p. 170-9.

·                  3.            Aiello, A.E., et al., Mask use, hand hygiene, and seasonal influenza-like illness among young adults: a randomized intervention trial. J Infect Dis, 2010. 201(4): p. 491-8.

·                  4.            Aiello, A.E., et al., Facemasks, Hand Hygiene, and Influenza among Young Adults: A Randomized Intervention Trial. PLoS ONE, 2012. 7(1): p. e29744.

·                  5.            Alfelali, M., et al., Facemask versus No Facemask in Preventing Viral Respiratory Infections During Hajj: A Cluster Randomised Open Label Trial. SSRN Electronic Journal, 2019.

·                  6.            Barasheed, O., et al., Pilot Randomised Controlled Trial to Test Effectiveness of Facemasks in Preventing Influenza-like Illness Transmission among Australian Hajj Pilgrims in 2011. Infect Disord Drug Targets, 2014. 14(2): p. 110-6.

·                  7.            Wang, M., et al., A cluster-randomised controlled trial to test the efficacy of facemasks in preventing respiratory viral infection among Hajj pilgrims. J Epidemiol Glob Health, 2015. 5(2): p. 181-9.

·                  8.            Al-Asmary, S., et al., Acute respiratory tract infections among Hajj medical mission personnel, Saudi Arabia. Int J Infect Dis, 2007. 11(3): p. 268-72.

·                  9.            Canini, L., et al., Surgical Mask to Prevent Influenza Transmission in Households: A Cluster Randomized Trial. PLoS ONE, 2010. 5(11): p. e13998.

·                  10.         Cowling, B.J., et al., Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial. Ann Intern Med, 2009. 151(7): p. 437-46.

·                  11.         Cowling, B.J., et al., Preliminary Findings of a Randomized Trial of Non-Pharmaceutical Interventions to Prevent Influenza Transmission in Households. PLoS ONE, 2008. 3(5): p. e2101.

·                  12.         MacIntyre, C.R., et al., A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open, 2015. 5(4): p. e006577.

·                  13.         MacIntyre, C.R., et al., A randomized clinical trial of three options for N95 respirators and medical masks in health workers. Am J Respir Crit Care Med, 2013. 187(9): p. 960-6.

·                  14.         Loeb, M., et al., Surgical mask vs N95 respirator for preventing influenza among health care workers: a randomized trial. Jama, 2009. 302(17): p. 1865-71.

·                  15.         Radonovich, L.J., Jr., et al., N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial. Jama, 2019. 322(9): p. 824-833.

·                  16.         Tunevall, T.G., Postoperative wound infections and surgical face masks: a controlled study. World J Surg, 1991. 15(3): p. 383-7; discussion 387-8.

·                  17.         Webster, J., et al., Use of face masks by non-scrubbed operating room staff: a randomized controlled trial. ANZ J Surg, 2010. 80(3): p. 169-73.


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