There’s an old story about a guy who jumped into a thorn bush: He wanted to collect berries, but he failed to consider the adverse effects of the plan. Something similar happened with face masks during the COVID-19 pandemic: Masks were promoted, and often mandated, as necessary safeguards for reducing the chance of infection, while their possible adverse effects were brushed aside. While the science on the benefits of masking is still inconclusive, the latest research now shows that the prolonged use of face masks—especially those with tighter fits like the N95s—could harm wearers by exposing them to dangerously high levels of carbon dioxide.
The risks appear to be especially pronounced for young people. As part of a team of scientists, one of the authors of this article conducted a randomized study of the effects of masking on healthy school aged children in Germany. The results of this research, published in September 2022 in the peer reviewed journal Environmental Research, concluded that wearing masks raised the carbon dioxide (CO₂) “content in inhaled air quickly to a very high level in healthy children in a seated resting position that might be hazardous to children’s health.”
These results should not have come as a surprise. It has long been suspected that mask-wearing poses risks. In Germany, for instance, workers required to wear an N95/FFP2 respirator must get a certificate verifying their ability to do so, and even with said certificate, those workers are mandated to take a 30-minute break every 90 minutes.
Only in the 19th century, with the development of germ theory, did masks begin being used as health devices. Then in the early 20th century, masks gained a foothold in hospitals, usually worn by doctors and nurses. The “Spanish flu” pandemic of 1918-20 was perhaps the first case of masks being worn by the general public, but we only have scattered photographic pictures of masked people and don’t know how frequently they were worn.
During the 20th century, most scientists believed that masks could be useful only in hospitals for the prevention of surgical wound infections in high-risk cases. Still in 2010, a study overseen by Dr. Ben Cowling, a professor of public health at the University of Hong Kong, found weak evidence, if any, that masks could be a useful tool for stopping airborne infections.
There’s thus every reason to believe that, in March 2020, when Dr. Anthony Fauci discouraged Americans from wearing masks, he was simply stating a widely accepted medical orthodoxy. Population-level mandatory face masking had never been attempted before, and there was no reliable data proving its effectiveness, nor data detailing its adverse effects. It was reasonable to be cautious before recommending such a drastic and untested solution.
Yet this attitude rapidly changed, most likely because of political factors. It is not that politicians were directly meddling with medicine; more likely, they simply wanted to be seen as “doing something.” Masks offered visible evidence that the leaders were acting against the pandemic, and so masks appeared to be a good idea. The medical authorities rapidly sensed what was expected of them—back up the politicos—and they complied, even in the absence of data supporting the decision.
After more than two years of widespread masking, which remained mandatory for young school children long after it was abandoned by the politicians who imposed such measures, we are starting to see more data. But many studies are of poor quality, performed on small populations, based on questionable assumptions, using debatable statistical methods, and often using air that is unnaturally saturated with viral particles.
Some studies do indicate that, at least in some conditions, masks can slow down the diffusion of the SARS-CoV-2 virus. Masks are not, however, a miracle device that can fully stop the virus. As doctors were saying in early 2020 before the public health establishment reversed its position on the issue, aerosol particles carrying the coronavirus are simply too small to be completely stopped by the filtering tissue of standard masks, and even less so because of how often masks are worn incorrectly.
It is our view, then, after considering the available scholarship, that we cannot establish any clear and conclusive benefits to widespread masking.
Can we establish the presence of any harmful effects? Here, we enter a complicated field of study, as it is difficult to determine the adverse effect of masks on wearers. Such a gap in knowledge is part of a pattern: In the history of medicine, there have been some glaring failures in detecting adverse effects. You may remember, for instance, the story of thalidomide, a drug marketed in the 1950s as a sedative, that was later found to cause birth defects. It had not been properly tested on pregnant women.
One problem with determining adverse effects is that you can’t knowingly expose people to something that you suspect causes serious harm, not even in the name of science. The Nuremberg Code, a set of international ethical principles created after the Doctors Trial for Nazi medical war crimes, prohibits experimentation on human subjects without their explicit consent. Another problem is that adverse effects are often delayed in time. Think of the health effects of cigarettes. Nobody ever died because they smoked one cigarette. After several decades of studies, however, it was possible to determine that if you are a smoker your life expectancy is reduced by a significant number of years.
Just like smoking a single cigarette never killed anyone, wearing a face mask for a few hours or a few days does not cause irreversible damage either. But the immediate short-term physiological effects are detectable: A recent study led by Pritam Sukul, senior medical scientist at the University Medicine Rostock in Germany, found masks to cause hypercarbia (high concentration of CO₂ in the blood), arterial oxygen decline, blood pressure fluctuations, and concomitant physiological and metabolic effects. On a time scale of weeks or months, these effects appear to be reversible. But how can we know what can happen to people who wear masks for several hours a day for several years? Will we have to wait for decades before concluding that masks are bad for people’s health, as was the case with cigarettes?
Not necessarily, for we are able to assess face masks in terms of the air quality breathed by the wearers. One important parameter for air quality is CO₂ concentration. Over the years, a lot of data has been accumulated in this field from miners, astronauts, submariners, and other people exposed to high concentrations of CO₂. Measurable negative effects on mental alertness already occur at CO₂ concentrations over 600 parts per million (ppm), which is only slightly higher than the average concentration in open air (a little more than 400 ppm). Values higher than 1,000-2,000 ppm are not recommended for living spaces, especially for children and pregnant women. 5,000 ppm is the commonly accepted limit in working environments or in submarines and spaceships. Concentrations in the range of 10,000-20,000 ppm are not immediately life-threatening but can only be withstood for short periods. Even higher concentrations may lead to loss of consciousness and death.
So what kind of CO₂ concentration are people exposed to when they wear a face mask? Measuring the concentration of CO₂ inside the small volume of a face mask while it is being used poses practical problems, and there are no standardised methods and procedures to evaluate this. Nevertheless, during the past few years, several papers dealing with this subject were published.
Some of these papers were criticised, but often baselessly. For instance, some fact checkers claimed that the same amount of CO₂ could be found without face masks in exhaled breath. This is true, but trivial. The studies mentioned above measured the amount of CO₂ in the inhaled air under face masks; the fact checkers measured the air exhaled. Other fact checkers provided a priori statements by “experts,” including a sports reporter.
Meanwhile, studies that rely on robust capnographic methods that calculate inhaled CO₂ levels from the end-tidal volume of CO₂ under strictly controlled conditions have corroborated our findings about elevated CO₂ levels in masks. In short, there is strong evidence that people wearing face masks, especially the FFP2/N95 type, breathe a concentration of carbon dioxide several times higher than the recommended concentration limits, in the range of over 5,000 ppm and often over 10,000 ppm. In other words, masks may multiply the external CO₂ concentration by a factor of 10, if not more.
Individuals wearing a tight, N95-style face mask are thus breathing air of comparable quality to the air in spacecrafts and submarines. Astronauts and submariners, though, are well trained and in peak physical condition; masks, meanwhile, are often worn by the elderly, the young, and people affected by chronic pathologies. A recent study of more than 20,000 German children who wore masks for an average of more than four hours per day showed that 68% of them reported these kinds of problems.
There are additional risks associated with face masks that should be considered, such as psychological effects and infections from pathogens accumulated in the mask tissue, but we believe that the increased concentrations of CO₂ breathed by mask-wearers is a clear and demonstrated adverse effect that should be known and considered when deciding policies. In short, face masks are not harmless.
Wearing a face mask is not a purely symbolic gesture like wearing a lapel pin or waving a flag, as some people have come to believe. It is not simply an expression of social solidarity, belief in science, or support for health care workers. It can have important adverse effects on health—especially in the case of N95s—and, at the very minimum, citizens should be alerted to the downsides of masking before they make up their minds on the issue. Face masks should be mandated only in special circumstances, and ordinary citizens should wear them only when there is a real and evident risk of infection.
Ugo Bardi is a former professor of physical chemistry at the University of Florence, Italy. He is a full member of the Club of Rome, an international organization dedicated to promoting a clean and prosperous world for all humankind, and the author, among other books, of The Seneca Effect (2017), Before the Collapse (2019), and The Empty Sea (2021). He has specific experience studying pollutants.
Harald Walach is a clinical psychologist, philosopher, and historian of science. He is currently a Professorial Research Fellow at the Next Society Institute of Kazimieras Simonavicius University in Vilnius, Lithuania. He has conducted a study measuring CO₂ content under face masks in children.