Are Masks Effective? The Science of Masking

Aug 30, 2021

For more than 18 months, we’ve been told that masks are important to prevent the spread of Covid and occasionally you may hear that masks are inadequate to prevent transmission of viral disease. Confused??? In this article, we follow journalist Jeffery Anderson as he digs into the science, methodologies of testing, and the results found when testing the efficacy of masks. This article ends with a list of reference materials.

In an August 11, 2021, City-Journal article, [7] Jeffrey Anderson reviewed the scientific evidence for universal masking, noting that on February 25, 2020, U.K. health authorities published guidance discouraging the use of masks even for health care workers in residential care facilities due to the fact that they don’t prevent viral spread.

Anderson quotes it as saying, “During normal day-to-day activities facemasks do not provide protection from respiratory viruses, such as COVID-19 and do not need to be worn by staff.”

Ditto for then-Surgeon General Jerome Adams, who February 29, 2020, tweeted: “Seriously people — STOP BUYING MASKS! They are NOT effective in preventing the general public from catching #Coronavirus.” [3] Adams has since deleted the tweet, but it lives in infamy all over the internet. [4,5,6]

Similarly, March 30, 2020, the executive director for the World Health Organization’s Health Emergency Program stated, “there is no specific evidence to suggest that the wearing of masks by the mass population has any particular benefit.” [8]

The rationale at the time was that surgical masks are not designed to protect the wearer or others against viral transmission, as the holes in the fabric are far larger than any virus. They’re merely meant to prevent a health care worker from inadvertently infecting a patient’s wound with bacteria-laden saliva or respiratory droplets. As reported by Anderson [9] :

“Public-health officials’ advice in the early days of Covid-19 was consistent with that understanding. Then, on April 3, 2020, Adams announced that the CDC was changing its guidance and that the general public should hereafter wear masks whenever sufficient social distancing could not be maintained.

 Many cities across the country, following new CDC guidance handed down amid a spike in cases nationally caused by the Delta variant, are once again mandating indoor mask-wearing for everyone, regardless of inoculation status.

The CDC further recommends that all schoolchildren and teachers, even those who have had Covid-19 or have been vaccinated, should wear masks …

How did mask guidance change so profoundly? Did the medical research on the effectiveness of masks change — and in a remarkably short period of time — or just the guidance on wearing them?”

Randomized Controlled Trials

First, let’s talk about scientific testing and how it is properly conducted. Randomized controlled trials (RCTs) have long been regarded as the gold standard in medical research, as they allow you to isolate a specific variable and reduce the ability of researchers to produce a preferred outcome.

The first and only COVID-19-specific randomized controlled surgical mask trial, [19,20] published November 18, 2020, undermined the official narrative that masking works. Interestingly, it found routine mask wearing may either reduce your risk of SARS-CoV-2 infection by as much as 46%, or it may increase your risk by 23%.

Either way, the vast majority — 97.9% of those who didn’t wear masks, and 98.2% of those who did — remained infection-free (well before mass vaccination began).

The study included 3,030 individuals assigned to wear a surgical face mask and 2,994 unmasked controls. Of them, 80.7% completed the study. Based on the adherence scores reported, 46% of participants always wore the mask as recommended, 47% predominantly as recommended and 7% failed to follow recommendations.

Among mask wearers, 1.8% ended up testing positive for SARS-CoV-2, compared to 2.1% among controls. When they removed those who did not adhere to the recommendations for use, the results remained the same — 1.8%, which suggests adherence makes no significant difference either.

Among those who reported wearing their face mask “exactly as instructed,” 2% tested positive for SARS-CoV-2 compared to 2.1% of the controls.

Another investigation [21] that compared caseloads between states with mask mandates and those without showed states with mask mandates had an average of 27 positive SARS-CoV-2 “cases” per 100,000 people, whereas states with no mask mandates had just 17 cases per 100,000. This too suggests mask mandates have no positive impact to speak of.

Curiously, RCTs have been rarely used when it comes to mask wearing. Why is that? Anderson reports [10] :

"In a ‘Science Brief’ [11] highlighting studies that ‘demonstrate that mask wearing reduces new infections’ and serving as the main public justification for its mask guidance, the CDC provides a helpful matrix of 15 studies — none RCTs.

The CDC instead focuses strictly on observational studies completed after Covid-19 began. In general, observational studies are not only of lower quality than RCTs but also are more likely to be politicized, as they can inject the researcher’s judgment more prominently into the inquiry and lend themselves, far more than RCTs, to finding what one wants to find.

A particular favorite of the CDC’s … is an observational (specifically, cohort) study [12] focused on two COVID-positive hairstylists at a beauty salon in Missouri.

The two stylists, who were masked, provided services for 139 people, who were mostly masked, for several days after developing Covid-19 symptoms. The 67 customers who subsequently chose to get tested for the coronavirus tested negative, and none of the 72 others reported symptoms.

This study has major limitations. For starters, any number of the 72 untested customers could have had COVID-19 but been asymptomatic, or else had symptoms that they chose not to report to the Greene County Health Department, the entity doing the asking.

The apparent lack of spread of COVID-19 could have been a result of good ventilation, good hand hygiene, minimal coughing by the stylists, or the fact that stylists generally, as the researchers note, ‘cut hair while clients are facing away from them.’

The researchers also observe that ‘viral shedding’ of the coronavirus ‘is at its highest during the 2 to 3 days before symptom onset.’ Yet no customers who saw the stylists when they were at their most contagious were tested for COVID-19 or asked about symptoms.

Most importantly, this study does not have a control group. Nobody has any idea how many people, if any, would have been infected had no masks been worn in the salon.”

More Non-RTC studies: Observational Cohort Studies

Another piece of evidence leaned on by the CDC is a survey, which is even lower-quality evidence than an observational cohort study.

“Mask supporters often claim that we have no choice but to rely on observational studies instead of RCTs, because RCTs cannot tell us whether masks work or not. But what they really mean is that they don’t like what the RCTs show,” Anderson writes.

Indeed, you’d be hard-pressed to find even a single RCT showing mask wearing has a notable benefit. Anderson goes through 14 RCTs, conducted around the world, that have investigated the effectiveness of masks against respiratory viruses, discussing their findings.

Among them is a French study [13] from 2010, which randomly placed sick patients and their household contacts into a mask group or a non-mask group. Adherence to the designated intervention was “good.”

Within one week, 15.8% of household contacts in the no-mask control group and 16.2% in the mask group developed an influenza-like illness. The 0.4% difference between the groups was statistically insignificant. According to the authors: “In various sensitivity analyses, we did not identify any trend in the results suggesting the effectiveness of facemasks.”

The CDC’s own data [14,15,16] also show 70.6% of COVID-19 patients reported “always” wearing a cloth mask or face covering in the 14 days preceding their illness; 14.4% reported having worn a mask “often.” So, a total of 85% of people who came down with COVID-19 had “often” or “always” worn a mask.

Handwashing Beats Masks and Mask-Plus-Handwashing Combo

A 2009 study [17] funded by the CDC added hand washing to the mix to see if mask wearing would work better in combination with hand hygiene. One group was instructed on the use of hand hygiene only, a second group used both handwashing and face masks, and a third group did nothing.

While the mask-plus-handwashing group fared statistically better than the control group in one measure, the handwashing-only group beat the control group to a statistically significant degree in two measures.

This suggests handwashing alone was actually the most effective measure. According to the authors, “no additional benefit was observed when facemask [use] was added to hand hygiene by comparison with hand hygiene alone.

The notion that handwashing alone beats even the combination of handwashing and mask wearing gained support in a 2011 study, [18] which discovered that among those who washed their hands and wore face masks, the secondary attack rate of influenza-like illness was double that of the control group, which did nothing.

Multivariate analysis showed the same thing, leading the authors to conclude that relative to the control group, the odds of infection among those wearing masks and washing their hands was “twofold in the opposite direction from the hypothesized protective effect.”

More Science

If you’re still on the fence about whether masks are advantageous to everyone, including young children, consider reading through some of the available medical literature. In addition to the research reviewed above, here’s a small sampling of what else you’ll find when you start searching for data on face masks as a strategy to prevent viral infection:

  • Surgical masks and N95 masks perform about the same A 2009 study [22] published in JAMA compared the effectiveness of surgical masks and N95 respirators to prevent seasonal influenza in a hospital setting; 24% of the nurses in the surgical mask group still got the flu, as did 23% of those who wore N95 respirators. 

  • “No evidence” masks prevent transmission of flu in a hospital setting In September 2018, the Ontario Nurses Association (ONA) won its second of two grievances filed against the Toronto Academic Health Science Network’s (TAHSN) “vaccinate or mask” policy. This information also appears to have been scrubbed from the internet, but it is available in Wayback archives. As reported by the ONA [23] :

“After reviewing extensive expert evidence submitted … Arbitrator William Kaplan, in his September 6 decision, [24] found that St. Michael’s VOM policy is ‘illogical and makes no sense’…  

In 2015, Arbitrator James Hayes struck down the same type of policy in an arbitration that included other Ontario hospitals across the province … Hayes found there was ‘scant evidence’ that forcing nurses to use masks reduced the transmission of influenza to patients…

ONA’s well-regarded expert witnesses, including Toronto infection control expert Dr. Michael Gardam, Quebec epidemiologist Dr. Gaston De Serres, and Dr. Lisa Brosseau, an American expert on masks, testified that there was … no evidence that forcing healthy nurses to wear masks during the influenza season did anything to prevent transmission of influenza in hospitals. 

They further testified that nurses who have no symptoms are unlikely to be a real source of transmission and that it was not logical to force healthy unvaccinated nurses to mask.”

  • No significant reduction in flu transmission when used in a community setting A policy review paper [25] published in Emerging Infectious Diseases in May 2020, which reviewed “the evidence base on the effectiveness of nonpharmaceutical personal protective measures … in non-health care settings” concluded, based on 10 randomized controlled trials, that there was “no significant reduction in influenza transmission with the use of face masks…” 

  • “No evidence” that universal masking prevents COVID-19 A 2020 guidance memo by the World Health Organization pointed out that [26] :

“Meta-analyses in systematic literature reviews have reported that the use of N95 respirators compared with the use of medical masks is not associated with any statistically significant lower risk of the clinical respiratory illness outcomes or laboratory-confirmed influenza or viral infections…

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.”

  • Mask or no mask, same difference A meta-analysis and scientific review [27] led by respected researcher Thomas Jefferson, cofounder of the Cochrane Collaboration, posted on the prepublication server medRxiv in April 2020, found that, compared to no mask, mask wearing in the general population or among health care workers did not reduce influenza-like illness cases or influenza.  In one study, which looked at quarantined workers, it actually increased the risk of contracting influenza, but lowered the risk of influenza-like illness. They also found there was no difference between surgical masks and N95 respirators.


If we are to follow the science — which is a good idea in general and particularly when it comes to public health mandates — the health benefits of wearing masks can certainly be questionable. As reported by Anderson [28] :

“In sum, of the 14 RCTs that have tested the effectiveness of masks in preventing the transmission of respiratory viruses, three suggest, but do not provide any statistically significant evidence in intention-to-treat analysis, that masks might be useful.

The other eleven suggest that masks are either useless — whether compared with no masks or because they appear not to add to good hand hygiene alone — or actually counterproductive.

Of the three studies that provided statistically significant evidence in intention-to-treat analysis that was not contradicted within the same study, one found that the combination of surgical masks and hand hygiene was less effective than hand hygiene alone, one found that the combination of surgical masks and hand hygiene was less effective than nothing, and one found that cloth masks were less effective than surgical masks.”

Some content from an article originally posted by Dr. Mercola on 8/23/21