Did a study prove that wearing face masks raises the risk of stillbirths, testicular dysfunction and cognitive decline "due to build-up of carbon dioxide" (CO2)? No, that's not true: A "study" shared widely to social media was actually a review article of existing scientific studies -- not directly related to mask-wearing -- that a medical expert told Lead Stories was "very selective in the literature" cited and that only included research that supported the author's claims.
Neither the review article nor the studies it cited presented substantial evidence that wearing masks caused the conditions listed because none directly tested humans who wore masks to either determine CO2 levels or the short- and long-term effects of exposure. The studies cited in the review largely tested CO2 exposure in animals -- and none of them were wearing masks.
The claim originated in a review article published in the scientific journal Heliyon on March 3, 2023, (archived here) that was later reported on by the British tabloid publication The Daily Mail on April 22, 2023 (archived here). Screenshots of The Daily Mail headline were later shared to social media. One such example included this post on Instagram on April 24, 2023, with a caption that read:
For all the trolls I tried to tell you that this would cause Health risk
Below is how the study appeared at the time of this writing:
(Source: Heliyon screenshot taken on Thurs April 27 04:41:00 UTC 2023)
Similar versions of the claim, which left out the important context and limitations of the review, were then reported by other outlets like ZeroHedge and Gulf Insider. Another example, The Daily Sceptic, copied text verbatim from The Daily Mail article, which included the below concerns:
But independent doctors have questioned the conclusions of the study -- which never directly looked at health complications and mask use, describing the link as 'unlikely' ...
But the study could not conclusively prove that the masks were directly responsible for any of these complications. ...
The main caveat of the research is that the studies looking at the potential toxic effects of carbon dioxide are animal studies - because these experiments would not be ethical in humans.
The researchers also noted that none of the studies in their review looked directly at mask use and miscarriages, infertility and neurodevelopment disorders.
The researchers also noted that the exact effects of toxic levels of CO2 on unborn life is not known in great detail.
Lead Stories emailed with Phil Chilibeck, a professor of kinesiology at the University of Saskatchewan whose work has included the physiological effects of wearing face masks during exercise, such as impacts to oxygen levels and breathing. The article in question "seems to be very selective in the literature" cited, he told Lead Stories on May 2, 2023, adding that the researchers did not include studies that would contradict their hypothesis.
The Heliyon article is not a study but rather a review article, which summarizes information and findings from previous studies. Review articles do not report on research conducted in a lab setting nor do they present experimental results that tested a hypothesis. A review article is meant to give an overview of existing scientific evidence available on a given topic.
So the Heliyon review did not establish a causal link between potential CO2 exposure from wearing face masks and associated health conditions because it did not directly test for CO2 levels that mask-wearing humans were exposed to, nor did the author determine potential health outcomes of such exposure.
"It is true that you are going to inhale a greater amount of CO2 while wearing a mask, but it is questionable whether this amount would result in any clinically important concern," explained Chilibeck, adding that his research group conducted a more thorough systematic review on exercise while wearing masks:
An advantage of a systematic review is that it is more objective than the scoping review done in the Heliyon article. We found that inhaled CO2 levels were increased, but not to clinically-meaningful levels (i.e. the levels were still within ranges considered safe), and from the studies we reviewed, there was no actual increase in levels of CO2 in the blood (probably because the amount of CO2 re-breathed with mask-wearing was not enough to elevate blood levels of CO2).
There are other more recent systematic reviews with similar findings that mask-wearing results in minimal increases in inhaled CO2 or blood levels of CO2, or increases that are too small to be of physiological concern.
The Heliyon article relied heavily on animal studies that included rats and guinea pigs as a means to suggest CO2 exposure would have similar effects in humans that wear masks.
"The Heliyon paper mentions studies in rodents where exposure to chronic low levels of CO2 affected pregnancy and testicular function. The limitation here is that the rodents were not wearing facemasks in these experiments and it is difficult to translate what is happening in rodents to what would happen in humans," Chilibeck told Lead Stories.
The Heliyon paper also cited as evidence that there was an increase in stillbirths during lockdowns. While this may be the case, Chilibeck adds that it is a "bit of a stretch" to attribute an increase in stillbirths to wearing face masks, particularly as some research has shown that COVID-19 infection may be associated with stillbirth rates and that access to health care was limited during the pandemic.
"During lockdowns, people ate poorer diets, consumed more alcohol, had greater sedentary behavior, and lower physical activity levels. Any of these changes could contribute to negative effects on health," explained Chilibeck. "Cognitive decline likewise could be attributable to other factors, such as a change to online learning and increased screen time."
The lead author of the Heliyon review article, Kai Kisielinksi, is described in a Research Gate biography as an "independent physician" from Dusseldorf, Germany. Kisielinksi has written other papers arguing that wearing masks may have harmful health effects. He did not respond to Lead Stories' emailed request for an interview.
Lead Stories has debunked a number of mask-related false claims, reporting that masks are not "Petri dishes for dangerous pathogens to fester," that a "gold standard" trial did not prove N95 and surgical masks were ineffective in preventing COVID transmission and that a Pfizer representative did not "admit" that COVID vaccines were "never tested on preventing transmission" (because vaccine clinical trials for drug approval are not meant to test that).