Updated: Sept. 2023
Published: July 2020
An overview of the current evidence regarding the effectiveness of face masks.
Contents
A) Studies ⇓ B) WHO review ⇓ C) Real-world evidence ⇓ D) N95/FFP2 masks ⇓ E) Additional aspects ⇓ F) The aerosol issue ⇓ G) Contrary evidence ⇓ H) Mask-related risks ⇓ I) Conclusion ⇓
A) Studies on the effectiveness of face masks
So far, most studies found little to no evidence for the effectiveness of face masks in the general population, neither as personal protective equipment nor as a source control.
- A May 2020 meta-study on pandemic influenza published by the US CDC found that face masks had no effect, neither as personal protective equipment nor as a source control. (Source)
- A WHO review of ten randomized controlled trials of face masks against influenza-like illness, published in September 2019, found no statistically significant benefit. (Source)
- A Danish randomized controlled trial with 6000 participants, published in the Annals of Internal Medicine in November 2020, found no statistically significant effect of high-quality medical face masks against SARS-CoV-2 infection in a community setting. (Source)
- A large randomized controlled trial with close to 8000 participants, published in October 2020 in PLOS One, found that face masks “did not seem to be effective against laboratory-confirmed viral respiratory infections nor against clinical respiratory infection.” (Source)
- A February 2021 review by the European CDC found no high-quality evidence in favor of face masks and recommended their use only based on the ‘precautionary principle’. (Source)
- A July 2020 review by the Oxford Centre for Evidence-Based Medicine found that there is no evidence for the effectiveness of face masks against virus infection or transmission. (Source)
- A November 2020 Cochrane review found that face masks did not reduce influenza-like illness (ILI) cases, neither in the general population nor in health care workers. (Source)
- An August 2021 study published in the Int. Research Journal of Public Health found “no association between mask mandates or use and reduced COVID-19 spread in US states.” (Source)
- An experimental study using virus aerosols, published in May 2022 in the Journal of Infectious Diseases, found that only professionally fit-tested N95/FFP2 masks, but not surgical masks or non-fitted N95/FFP2 masks, reduced viral loads in nostrils. (Source)
- A large Spanish school study, published in March 2022, found that “mask mandates in schools were not associated with lower SARS-CoV-2 incidence or transmission.” (Source)
- A May 2020 article by researchers from Harvard Medical School, published in the New England Journal of Medicine, concluded that face masks offer “little, if any, protection”. (Source)
- A 2015 study in the British Medical Journal BMJ Open found that cloth masks were penetrated by 97% of particles and may increase infection risk by retaining moisture or repeated use. (Source)
For a review of studies claiming face masks are effective, see section G) below.
Update: In January 2023, an updated Cochrane review found that there was still no evidence for the effectiveness of medical masks or N95 masks against SARS-CoV-2 or influenza virus. (Source)
B) WHO review of face mask trials (2019)
In September 2019, shortly before the coronavirus pandemic, the World Health Organization (WHO) published a comprehensive report on “Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza”.
The report reviewed ten randomized controlled trials concerning the effectiveness of face masks against influenza-like illness (ILI). As the following table shows, none of the trials found a statistically significant benefit of face masks.
C) Development of cases after mask mandates
In many states, coronavirus infections strongly increased after mask mandates had been introduced. The following charts show the typical examples of Austria, Belgium, France, Germany, Ireland, Italy, Spain, the UK, California and Hawaii. Furthermore, a direct comparison between US states with and without mask mandates indicates that mask mandates have made no difference. (Charts: Y. Weiss)
For an updated version of these charts, see the postscript below.
D) Effectiveness of N95/FFP2 mask mandates
In January 2021, the German state of Bavaria was one of the first places in the world to mandate N95/FFP2 masks in most public settings. A comparison with other German states, which required cloth or medical masks, indicates that even N95/FFP2 masks have made no difference.
In January 2021, Austria was the first country in the world to introduce an N95/FFP2 mask mandate at the national level. The mandate was further expanded in September 2021. Nevertheless, by November 2021 Austria reported the highest infection rate in the world.
E) Additional aspects
- There is increasing evidence that the novel coronavirus is transmitted, at least in indoor settings, not primarily by droplets but by much smaller aerosols. However, due to their large pore size and poor fit, most face masks cannot filter out aerosols (see video analysis below): over 90% of aerosols penetrate or bypass the mask and fill a medium-sized room within minutes.
- The WHO admitted to the BBC that its June 2020 mask policy update was due not to new evidence but “political lobbying”: “We had been told by various sources WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying. This point was put to WHO who did not deny.” (D. Cohen, BBC Medical Corresponent).
- To date, the only randomized controlled trial (RCT) on face masks against SARS-CoV-2 infection in a community setting found no statistically significant benefit (see above). However, three major journals refused to publish this study, delaying its publication by several months.
- An analysis by the US CDC found that 85% of people infected with the new coronavirus reported wearing a mask “always” (70.6%) or “often” (14.4%). Compared to the control group of uninfected people, always wearing a mask did not reduce the risk of infection.
- Researchers from the University of Minnesota found that the infectious dose of SARS-CoV-2 is just 300 virions (virus particles), whereas a single minute of normal speaking may generate more than 750,000 virions, making face masks unlikely to prevent infection.
- Contrary to common belief, studies in hospitals found that the wearing of a medical mask by surgeons during operations didn’t reduce post-operative bacterial wound infections in patients.
- Many health authorities argued that face masks suppressed influenza; in reality, influenza was temporarily displaced by the more infectious coronavirus. Indeed, influenza disappeared even in states without masks, lockdowns and school closures (e.g. Sweden and Florida).
- The initially low coronavirus infection rate in some Asian countries was not due to masks, but due to very rapid border controls. For instance, Japan, despite its widespread use of face masks, had experienced its most recent influenza epidemic just one year prior to the covid pandemic.
- Early in the pandemic, the advocacy group “Mask for All” argued that Czechia had few infections thanks to the early use of masks. In reality, the pandemic simply hadn’t reached Eastern Europe yet; a few months later, Czechia had one of the highest infection rates in the world.
- During the notorious 1918 influenza pandemic, the use of face masks among the general population was widespread and in some places mandatory, but they made no difference.
F) The facemask aerosol issue
In the following video, Dr. Theodore Noel explains the facemask aerosol issue. (Source)
G) Studies claiming face masks are effective
Some recent studies argued that face masks are indeed effective against the new coronavirus and could at least prevent the infection of other people. However, most of these studies suffer from poor methodology and sometimes show the opposite of what they claim to show.
Typically, these studies ignore the effect of other measures, the natural development of infection rates, changes in test activity, or they compare places with different epidemiological conditions. Studies performed in a lab or as a computer simulation often aren’t applicable to the real world.
An overview:
- A meta-study in the journal Lancet, commissioned by the WHO, claimed that masks could reduce the risk of infection by 80%, but the studies considered mainly N95 respirators in a hospital setting, not cloth masks in a community setting, the strength of the evidence was reported as “low”, and experts found numerous flaws in the study. Professor Peter Jueni, epidemiologist at the University of Toronto, called the WHO study “essentially useless”.
- A study in the journal PNAS claimed that masks had led to a decrease in infections in three global hotspots (including New York City), but the study did not take into account the natural decrease in infections and other simultaneous measures. The study was so flawed that over 40 scientists recommended that the study be withdrawn.
- A US study claimed that US counties with mask mandates had lower Covid infection and hospitalization rates, but the authors had to withdraw their study as infections and hospitalizations increased in many of these counties shortly after the study was published.
- A large study run in Bangladesh claimed that surgical masks, but not cloth masks, reduced “symptomatic SARS-CoV-2 infections” by 0.08% (ARR), and only in people over 50. But a subsequent re-analysis found that there was in fact no benefit at all. According to one reviewer, the Bangladesh study was designed so poorly that it “ended before it even began”.
- A German study claimed that the introduction of mandatory face masks in German cities had led to a significant decrease in infections. But the data did not support this claim: in some cities there was no change, in others a decrease, in others an increase in infections (see graph below). The city of Jena was an ‘exception’ only because it simultaneously introduced the strictest quarantine rules in Germany, but the study did not mention this.
- A review by the University of Oxford claimed that face masks are effective, but it was based on studies about SARS-1 and in health care settings, not in community settings.
- A review by members of the lobby group ‘Masks for All’, published in the journal PNAS, claimed that masks are effective as a source control against aerosol transmission in the community, but the review provided no real-world evidence supporting this proposition.
- A study published in Nature Communications in June 2021 claimed that masks reduced the risk of infection by 62%, but the study relied on self-reported online survey results and various modelling assumptions, not on actual measurements.
- A meta-study published in BMJ claimed face masks reduced infections by 53%, but the meta-study was based on seven low-quality observational studies. In response, the BMJ published an editorial acknowledging the “lack of good research” and the implausibility of the result.
- A German study, published in PNAS, claimed that N95/FFP2 masks are highly effective against coronavirus infections, but the study consisted only of a mathematical model without any real-world or lab data (see section D above).
- A study published by the US CDC claimed that face masks reduced covid infections in schools, but when the study was updated with more data, the effect disappeared.
- A study published in PNAS acknowledged that mask mandates weren’t effective, but claimed that mask wearing was effective. But the study relied on unvalidated self-reporting and modelling, not on actual data, and covered only the period from May to September 2020.
The annex of the German Jena study showed that face masks weren’t effective:
H) Risks associated with face masks
Wearing masks for a prolonged period of time may not be harmless, as the following evidence shows:
- The WHO warns of various “side effects” such as difficulty breathing and skin rashes.
- A South Korean study, published in May 2023, found that N95 masks can release toxic volatile organic compounds (TVOC) at levels eight times higher than considered safe.
- A Japanese study, published in Nature Scientific Reports, found a significant number of bacteria and fungi on face masks, including some pathogenic microbes.
- An Israeli-Canadian study, published in Cognitive Research in February 2022, found that “face masks disrupt holistic processing and face perception in school-age children”.
- An Italian study using real-time capnography found that face masks and N95/FFP2 masks increased CO2 levels in inhaled air to levels above the acceptable exposure threshold.
- A study conducted by the University Hospital of Leipzig in Germany found that surgical masks and N95 masks significantly reduce the resilience and performance of healthy adults.
- The Hamburg Environmental Institute warned of the inhalation of chlorine compounds in polyester masks as well as environmental issues in connection with face mask disposal.
- The European rapid alert system RAPEX has already recalled over 100 mask models because they did not meet EU quality standards and could lead to “serious risks”.
- A study by the University of Muenster in Germany found that on N95 (FFP2) masks, Sars-CoV-2 may remain infectious for several days, thus increasing the risk of self-contamination.
- In China, several children who had to wear a mask during gym classes fainted and died; autopsies found a sudden cardiac arrest as the probable cause of death. In the US, a car driver wearing an N95 (FFP2) mask fainted and crashed due to CO2 intoxication.
Video: A mask-wearing, 19-year-old US athlete collapsed during an 800-meter run (April 2021):
Conclusion
Face masks in the general population might be effective, at least in some circumstances, but there is currently little to no evidence supporting this proposition. If the coronavirus is primarily transmitted via indoor aerosols, face masks are unlikely to be protective. Thus, health authorities should not assume or suggest that face masks will reduce the rate or risk of infection.
United States: mask mandates without benefit
Postscript (August 2021)
A long-term analysis shows that infections have been driven primarily by seasonal and endemic factors, whereas mask mandates and lockdowns have had no discernible impact (charts: IanMSC).
Further reading
- The face mask folly in retrospect (August 2021)