Face Mask Science

Authored by
Staff
Last reviewed
July 20, 2021

Face Mask Science

Face masks are a simple barrier to help prevent respiratory droplets from reaching other people. Studies show that masks reduce droplets' spray when worn over the nose and mouth when inside.

However, the New York Times wrote on May 6, 2021, 'There is not a single documented Covid infection anywhere in the world from casual outdoor interactions, such as walking past someone on the street or eating at a nearby table.'

And the U.S. CDC stated on February 18, 2021: 'wearing face masks may 'not' be necessary when outside by yourself, away from others, or with other people who live in your household. As 'data regarding the “real-world” effectiveness of community masking are limited to observational and epidemiological studies.'

Studies Defining Clinical Benefits Wearing Face Masks When Outside

July 13, 2021 - The Annals of Internal Medicine published Update Alert #6: Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings. No new studies done in a community setting were identified through literature searches. In community settings, the strength of evidence remains low for an association between any mask use versus no mask use or surgical mask use versus no mask use and decreased risk for SARS-CoV-1 infection. 

June 10, 2021 - The U.S. CDC announced that, until it can amend the Order, it will exercise its enforcement discretion not to require wearing a mask in outdoor areas of transportation conveyances (if such outdoor areas exist on the conveyance) or while outdoors at transportation hubs. The CDC continues to recommend wearing masks in these areas by people who are not fully vaccinated.

April 13, 2021 - A Washington Post article concluded it is safer for people to be outside without wearing face masks.

April 5, 2021 - HPSC data, provided in response to a query from The Irish Times, reported one confirmed case of Covid-19 in every thousand is traced to outdoor transmission, new figures reveal. Of the 232,164 cases of Covid-19 recorded up to March 24, 2021, 262 were due to outdoor transmission, representing 0.1% of the total. University of Canterbury, Prof Mike Weed studied 27,000 Covid-19 cases based on 6,000 different pieces of data. One study was of 7,500 cases in China and Japan before lockdown in both of those countries. The number of cases associated with an outdoor transmission was “so small to be insignificant,” he discovered.

December 10, 2020 - The London Medicine: out of a total of 1,576 superspreading event entries, 1,493 (94.7%) were classified as “Indoor,” 63 were “Indoor/Outdoor,” 4 were “Outdoor.

December 8, 2020 - On average, assuming several infected people equal to 10% of the population, the time necessary to inspire a quantum (i.e., the dose of airborne droplet nuclei required to cause infection in 63% of susceptible persons) would be 31.5 days in Milan (range 2.7–91 days) and 51.2 days in Bergamo (range 4.4–149 days). Therefore, the probability of airborne transmission due to respiratory aerosol is very low in outdoor conditions..”

November 29, 2020 - A Systematic Review of outdoor transmission SARS-CoV-2 and other respiratory virus studies. Five identified studies found that a low proportion of reported global SARS-CoV-2 infections have occurred outdoors (<10%). Five studies described influenza transmission outdoors, and 2 described adenovirus transmission outdoors. There was high heterogeneity in study quality and individual definitions of outdoor settings, which limited our ability to conclude outdoor transmission risks. In general, factors such as duration and frequency of personal contact, lack of personal protective equipment, and occasional indoor gathering during a largely outdoor experience were associated with outdoor infection reports. The researchers concluded by stating: 'there are significant gaps in our understanding of specific pathways. These results suggest that moving activities to outdoor settings may reduce (SARS-CoV-2) infections and ultimately save lives.'

November 18, 2020 - A study published by the Annals of Internal Medicine reported a total of 3,030 participants were randomly assigned to wear masks, and 2,994 were assigned to control; Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%). The difference observed was not statistically significant.

September 10, 2020 - A non-peer-reviewed study of a database of more than 20,000 cases (including the 7,324 Chinese cases) found 461 (6%) associated with coronavirus transmissions during completely outdoor environments.

May 17, 2020 - Study: Although mechanistic studies support the potential effect of hand hygiene or face masks, evidence from 14 randomized controlled trials of these measures did not support a substantial effect on the transmission of laboratory-confirmed influenza.

Face Mask Use When Inside

July 19, 2021 - The American Academy of Pediatrics strongly recommended in-person learning and issued a recommendation that everyone older than age 2 wear face masks, regardless of vaccination status.

July 16, 2021 - The Research Letter, “Experimental Assessment of Carbon Dioxide Content in Inhaled Air With or Without Face Masks in Healthy Children: A Randomized Clinical Trial,” by Harald Walach, Ph.D., and colleagues, published online in JAMA Pediatrics on June 30, 2021, is hereby retracted. Following publication, numerous scientific issues were raised regarding the study methodology, including concerns about the applicability of the device used for assessment of carbon dioxide levels in this study setting and whether the measurements obtained accurately represented carbon dioxide content in inhaled air, as well as issues related to the validity of the study conclusions. 

July 13, 2021 - The Annual of Internal Medicine published its update #6. New evidence from a cross-sectional study done in France found that consistent face mask use compared with inconsistent use was associated with a reduced risk for SARS-CoV-2 infection (adjusted odds ratio, 0.07 [CI, 0.003 to 0.56]).

June 30, 2021 - The JAMA Pediatrics published a Research Letter - Experimental Assessment of Carbon Dioxide Content in Inhaled Air With or Without Face Masks in Healthy Children. The Figure shows that the child's value with the lowest carbon dioxide level was 3-fold greater than the limit of 0.2 % by volume. The youngest children had the highest values, with one 7-year-old child’s carbon dioxide level measured at 25 000 ppm.

May 28, 2021 - The U.S. CDC stated, 'Fully vaccinated people can resume activities without wearing masks.'

May 13, 2021 - The Centers for Disease Control and Prevention (CDC) says that you don't need to wear masks indoors or outside if you are fully vaccinated. "Anyone who is fully vaccinated can participate in indoor and outdoor activities, large or small, without wearing a mask or physical distancing," CDC Director Rochelle Walensky said during a White House briefing.

April 28, 2021 -  A certain percentage of children and adolescents have non-negligible complaints when wearing the mask. These children should not be stigmatized. This worldwide first registry on side effects of the mask reflects the spectrum of symptoms in children and adolescents. A precise benefit-risk analysis is urgently required. The occurrence of reported side effects in children due to wearing the masks must be taken seriously and requires a precise clarification of the accompanying health circumstances, wearing the mask (duration, breaks, and mask type), and the school situation. Furthermore, all parents, doctors, pedagogies, and others are invited to participate in www.co-ki-masken.de to document their observations on the effects of wearing the mask. This study is based on a survey regarding the adverse effects of mask-wearing in children. Due to multiple limitations, this study cannot demonstrate a causal relationship between mask-wearing and the reported adverse effects on children.

April 2, 2021 - According to a study published in The Journal of Infectious Diseases, 'Aerosol transmission is affected by more than decay rate, though, the researchers cautioned. The amount of virus emitted, the origins of the viral particles (e.g., lung vs. saliva), mutations changing which cells the virus affects, and other factors can change transmissibility. "There were no differences in the decay constants between isolates in darkness at either 20°C or 40°C, with a mean time for a 90% loss of viral infectivity across all dark conditions of 6.2 hours." Despite the small difference, these data suggest that the SARS-CoV-2 lineages represented by all four isolates would be rapidly inactivated by natural sunlight in real-world scenarios.

March 26, 2021 - A study published in the Journal of Occupational and Environmental Medicine from researchers at Henry Ford Health System has found that Henry Ford’s early implementation of a universal mask policy in the COVID-19 pandemic was strongly associated with reducing the risk of healthcare workers when inside at Henry Ford acquiring COVID-19. 

March 11, 2021 - Scientists detail three cases of COVID-19 despite the use of PPE in a study published in Clinical Infectious Diseases. The Massachusetts Department of Public Health sequenced the genomes of SARS-CoV-2 specimens from patients and employees at Brigham and Women's Hospital. This spread occurred despite one or both parties wearing ASTM Level 1 masks with ear loops. These masks are designed to filter 95% of bacteria and 0.1-micrometer particles. Whole-genome sequencing confirmed perfect homology between source and exposed persons’ viruses in all cases.

March 9, 2021 - The Annal of Internal Medicine published the fifth update alert, for a living rapid review on the use of masks to prevent respiratory virus infections, including SARS-CoV-2, in health care and community settings. This Alert found the strength of evidence for any mask use versus nonuse in community settings remains low. Other strength-of-evidence ratings related to mask use in community settings were unchanged because of no new evidence.

February 5, 2021 - The U.S. CDC reported during March 22–October 17, 2020, 10 sites participating in the COVID-19–Associated Hospitalization Surveillance Network in states with statewide mask mandates reported a decline in weekly COVID-19–associated hospitalization growth rates by up to 5.5 percentage points for adults aged 18–64 years after mandate implementation, compared with growth rates during the 4 weeks preceding implementation of the mandate.

January 19, 2021 - The effect of mask-wearing on community transmission of SARS-CoV-2 has been the subject of substantial debate, despite evidence of its potential effect to reduce SARS-CoV-2 spread from detailed transmission studies and population-wide data from other respiratory pathogens. Our evidence supports the role of mask-wearing in controlling SARS-CoV-2 transmission; however, this ecological study cannot inform questions of causality or generalizable biological mechanisms. In addition, it is difficult to disentangle individuals' engagement in mask-wearing from their adoption of other preventive hygiene practices, and mask-wearing might be serving as a proxy for other risk avoidance behaviors not queried (e.g., avoiding crowded spaces).

January 11, 2021 - a study published by PNAS stated, 'The science around the use of masks by the public to impede COVID-19 transmission is advancing rapidly. We recommend adopting public cloth mask-wearing as an effective form of source control. Because many respiratory particles become smaller due to evaporation, we recommend increasing focus on a previously overlooked aspect of mask usage: mask-wearing by infectious people (“source control”) with benefits at the population level, rather than only mask-wearing by susceptible people, such as health care workers, with focus on individual outcomes. We recommend that public officials and governments strongly encourage the use of widespread face masks in public, including the use of appropriate regulation.'

December 29, 2020 - This is the fourth update alert for a living rapid review on the use of masks for the prevention of respiratory virus infections, including SARS-CoV-2, in healthcare and community settings. The evidence for various comparisons about mask use in health care settings and risk for SARS-CoV-2 remains insufficient.

A study published on December 21, 2020, provides evidence for quantitative and qualitative changes in how humans process other people when wearing face masks. Researchers from the Ben-Gurion University of the Negev found that the success rate of identifying someone wearing a mask was reduced by 15%. 'The changes in performance, together with the alteration and the processing style of partially occluded faces, could have significant effects on daily living activities, including social interactions, as well as other situations involving personal interactions such as education, stated these researchers.'

December 8, 2020 - The Lancet study:  SARS-CoV-2 infection and transmission in educational settings: a prospective, cross-sectional analysis of infection clusters and outbreaks in England. 'SARS-CoV-2 infections and outbreaks were uncommon in educational settings during the summer half-term in England.'

December 4, 2020 -  Summary of CDC Guidance for Public Health Strategies to Address High Levels of Community Transmission of SARS-CoV-2 and Related Deaths, December 2020.  Face mask use is most important in indoor spaces and outdoors when a physical distance of ≥6 feet cannot be maintained. Within households, face masks should be used when a household member is infected or has had recent potential COVID-19 exposure (e.g., known close contact or potential exposure related to occupation, crowded public settings, travel, or nonhousehold members in your house.

December 3, 2020 - Study published by PNAS: 'We believe (quasi-experimental control group) that the reduction in the daily growth rates of infections between 47% and 70% is our best estimate of the effects of face masks' use in the Jena area of Germany, (pop 111,000) which may be a unique case.' The reported trajectories of synthetic Jena in Fig. 3A leave us with some degree of ambiguity in our analysis. Obviously, Jena's COVID-19 development's estimated difference vis-à-vis the synthetic Jena is only convincing if potentially concurrent policies other than masks can be ruled out. A methodical limitation is that estimates are only carried out in a “before-after” manner with no strict control group approach. This may limit the causal interpretation of results. Therefore, we provide causal evidence identifying the population impact of mandatory face masks on the spread of COVID-19.

December 3, 2020 - Governor John Carney and the Delaware Division of Public Health announced it would institute a universal mask mandate statewide, requiring Delawareans to wear a cloth face-covering anytime they are indoors with anyone outside their immediate household.

November 29, 2020 - Study summary: Existing evidence supports the wide-held belief that the risk of SARS-CoV-2 transmission is lower outdoors. The odds of indoor transmission were very high compared to outdoors (18.7 times; 95% CI 6.0, 57.9). 

November 20, 2020 - Trends in County-Level COVID-19 Incidence in Counties With and Without a Mask Mandate — Kansas, June 1–August 23, 2020.

November 20, 2020 - CDC Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2. 'Data regarding the “real-world” effectiveness of community masking are limited to observational and epidemiological studies.'

November 16, 2020 - Study: Evidence of Long-Distance Droplet Transmission of SARS-CoV-2 by Direct Air Flow in a Restaurant in Korea. Droplet transmission can occur at a distance greater than 2m if there is direct airflow from an infected person.

October 31, 2020 - In this study, we identified the outbreaks from these case reports from the local Municipal Health Commissions of 320 prefectural cities (municipalities) in China, not including Hubei Province, between January 4 and February 11, 2020. We also reviewed the major characteristics of the enclosed areas in which these outbreaks were determined and their associated indoor environmental aspects.

August 14, 2020 - Mask or no mask for COVID-19: A public health and market study.

August 3, 2020 - The Lancet: 'no intervention is associated with affording complete protection from infection; a combination of measures will always be required, now and during the next pandemic.'

August 2020 - A rapid systematic review of face masks and respirators' efficacy against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers, and sick patients.

July 9, 2020 - Quantitative Method for Comparative Assessment of Particle Removal Efficiency of Fabric Masks as Alternatives to Standard Surgical Masks for PPE.

July 6, 2020 - Face masks for community use: An awareness call to the materials' differences.

July 4, 2020 - In East Asian nations, the public practice became widespread in 2003 when SARS, another coronavirus variant, spread from China to neighboring countries.

June 16, 2020 - This study provides evidence from a natural experiment on the effects of state government mandates for face mask use in public issued by fifteen states plus Washington, D.C., between April 8 and May 15, 2020.

May 21, 2020 - Effectiveness of Common Fabrics to Block Aqueous Aerosols of Virus-like Nanoparticles.

On November 24, 2020, the FDA published Face Masks, Including Surgical Masks and Respirators for COVID-19, a comprehensive webpage on FDA.gov with answers to frequently asked questions about face masks, surgical masks, and respirators. 

The US Centers for Disease Control and Prevention (CDC) stated on November 8, 2020, everyone 2-years of age and older should wear a mask in public settings and when they are around people who do not live in their household.' As of November 20, 2020, 37 US states mandating face coverings in public, reports the AARP.

Note: This content is aggregated from various FDA, CDC, WHO, university, association, news services, and other third-party information publishers.