There is very limited research on the effectiveness of masks or the potential harms of their prolonged use in the general public. The available literature indicates little scientific evidence that mask-wearing among the general public curbs disease spread. There is mounting evidence for the potential harms of mask wearing. Recent reviews and studies are summarized here.
Non-pharmaceutical measures for pandemic influenza in non-healthcare settings—personal protective and environmental measures
Policy Review by Centers for Disease Control and Prevention
“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., May 2020)
Advice on the use of masks in the context of COVID-19
Interim Guidance by The World Health Organisation
“At present, there is no direct evidence (from studies on COVID-19 and in healthy people in the community) on the effectiveness of universal masking of healthy people in the community to prevent infection with respiratory viruses, including COVID-19.” (WHO, June 2020)
Physical interventions to interrupt or reduce the spread of respiratory viruses
Systemic Review by Cochrane
“The pooled results of  randomised trials did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal influenza. There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers when used in routine care to reduce respiratory viral infection.” (Jefferson et al., November 2020)
Masking lack of evidence with politics
Review by The Center for Evidence-Based Medicine, University of Oxford
“It would appear that despite two decades of pandemic preparedness, there is considerable uncertainty as to the value of wearing masks.” (Jefferson & Heneghan, 2020)
Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers
Randomized control trial reveals a non-statistically significant difference between two groups of participants, one requested to wear a mask, the other not wearing a mask. “masks would not be effective against spread via aerosols, which might penetrate or circumnavigate a face mask” “The data were compatible with lesser degrees of self-protection.” (Bundgaardet al., March 2020)
Mask mandate and use efficacy in state-level COVID-19 containment
“Case growth was not significantly different between [mask] mandate and non-mandate states at low or high transmission rates, and surges were equivocal.” (Guerra & Guerra, May 2020)
Mask use in the context of COVID-19
Interim Guidance by the WHO
The WHO lists mask disadvantages: discomfort, headaches, breathing difficulties, self-contamination, facial lesions, a false sense of security and poor compliance, difficulty with communication, among others (WHO, December 2020).
“Several studies have demonstrated statistically significant deleterious effects on various cardiopulmonary physiologic parameters during mild to moderate exercise in healthy subjects and in those with underlying respiratory diseases.” (WHO, December 2020).
Corona children studies “Co-Ki”: First results of a Germany-wide registry on mouth and nose covering (mask) in children
“Impairments caused by wearing the mask were reported by 68% of the parents. These included irritability (60%), headache (53%), difficulty concentrating (50%), less happiness (49%), reluctance to go to school/kindergarten (44%), malaise (42%) impaired learning (38%) and drowsiness or fatigue (37%).” (Schwarz et al., April 2021).
Experimental assessment of carbon dioxide content in inhaled air with or without face masks in healthy children
A Randomized Clinical Trial
According to the German Federal Environmental Office, the normal content of carbon dioxide (CO2) is 400 ppm (parts per million) in open air and a maximum limit of 2000 ppm for indoor space. The lowest level detected in a child was 3 times higher than the maximum limit.
“Most of the complaints reported by children can be understood as consequences of elevated carbon dioxide levels in inhaled air. This is because of the dead-space volume of the masks, which collects exhaled carbon dioxide quickly after a short time. This carbon dioxide mixes with fresh air and elevates the carbon dioxide content of inhaled air under the mask, and this was more pronounced in this study for younger children.” (Walach et al., June 2021).
Contamination by respiratory viruses on outer surface of medical masks used by hospital healthcare workers
“Commonly isolated viruses from masks samples were adenovirus (n = 7), bocavirus (n = 2), respiratory syncytial virus (n = 2) and influenza virus (n = 2). Virus positivity was significantly higher in masks samples worn for > 6 h.” “Respiratory pathogens on the outer surface of the used medical masks may result in self-contamination. The risk is higher with longer duration of mask use (> 6 h) and with higher rates of clinical contact [contact with patients].” (Chughtai et al., 2019).
Concerned parents sent 6 face masks worn by their children to the University of Florida Lab for analysis of contaminants. This report, prepared by Jennifer Cabrera in June 2021, details the findings.
“The analysis detected the following 11 dangerous pathogens on the masks: Streptococcus pneumoniae (pneumonia), Mycobacterium tuberculosis (tuberculosis), Neisseria meningitidis (meningitis, sepsis), Acanthamoeba polyphaga (keratitis and granulomatous amebic encephalitis), Acinetobacter baumanni (pneumonia, bloodstream infections, meningitis, UTIs—resistant to antibiotics), Escherichia coli (food poisoning), Borrelia burgdorferi (causes Lyme disease), Corynebacterium diphtheriae (diphtheria), Legionella pneumophila (Legionnaires’ disease), Staphylococcus pyogenes serotype M3 (severe infections—high morbidity rates), Staphylococcus aureus (meningitis, sepsis)”.
WHAT ABOUT PAPERS CLAIMING MASKS WORK?
Many studies that claim masks work employ poor methodologies. They are usually conducted in highly controlled and artificial laboratory settings or in hospitals. Strict adherence to study protocols is required yet these protocols cannot be respected by the general population wearing masks in a community setting.
Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021
“Cloth masks and medical procedure masks substantially reduce exposure from infected wearers (source control) and reduce exposure of uninfected wearers (wearer exposure).” (Brooks et al., 2021)
Refutation of Brooks et al.
The researchers admit a major shortcoming as the first “limitation” of the study, namely that the findings should not be generalised or interpreted as being representative of mask effectiveness in real-world settings. The study was conducted in a very controlled, static environment with plastic heads and only 2 specific types of masks, making it impossible to extrapolate these findings to the real world with living, breathing, moving people in dynamic environments, using a variety of mask materials with a wide range of fit. The researchers admit that “The extent to which [masks] reduce exhalation and inhalation of particles in the aerosol size range varies substantially, in part because air can leak around their edges, especially through the side gaps.” The researchers further admit that “double masking might impede breathing or obstruct peripheral vision”. This CDC study is reminiscent of a high school science fair exhibit.
Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis
“Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m; protection was increased as distance was lengthened. Face mask use could result in a large reduction in risk of infection, with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar. Eye protection also was associated with less infection.” (Chu et al., June 2020)
Refutation of Chu et al.
by Swiss Policy Research here
Face masks considerably reduce COVID-19 cases in Germany
“Depending on the region we consider, we find that face masks reduced the number of newly registered severe acute respiratory syndrome coronavirus 2 infections between 15% and 75% over a period of 20 days after their mandatory introduction. Assessing the credibility of the various estimates, we conclude that face masks reduce the daily growth rate of reported infections by around 47%.” (Mitze et al., 2020)
Refutation of Mitze, et.al.
A tell-tale sign of cherry-picked data being selected for a study is the inclusion of data from n-days in combination with what the authors describe as a “synthetic control method”. This type of study design begs the question of how that particular number of days was decided upon, and how the results might have been different for 25 days, or 15 days or an altogether different 20-day period? This plot illustrates the point, using publicly available data. To examine the data directly, please visit COVID-19 Data Explorer – Our World in Data, and look at Germany’s data using “cumulative confirmed cases.” As the snapshot below illustrates, the graph bends during the study period, but illustrates a very different outcome soon thereafter – almost as if the authors only selected the data range that supports their desired conclusion. It may be that other portions of this study design, i.e., statistical approach, could be flawed, but such deep-diving seems unnecessary.