Three years after a global pandemic prompted public health officials to recommend widespread mask-wearing, social media users warned that people who wore masks unknowingly subjected themselves to potentially devastating health risks.

They shared an April 22 Daily Mail story headlined, “Face masks may raise risk of stillbirths, testicular dysfunction and cognitive decline due to build-up of carbon dioxide, study warns.”

The story called it “explosive new research.” But worried mask-wearers should take a deep breath: The referred-to study— which was actually an article that reviewed studies — presents no evidence that masks caused serious health problems.

The headline was shared on Instagram and copied in similar posts, which were flagged as part of Meta’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.)

The Daily Mail story discussed a German research article published March 3 in a publication called Cell Press.

A Cell Press spokesperson told us the article was peer-reviewed.

The article, which reviewed 43 studies on carbon dioxide exposure, reached no hard conclusions. It issued a warning about “mandatory daily long-term use of masks, especially for children, adolescents, younger people and pregnant women,” and referred to “data indicating testicular toxicity in adolescents.”

“Circumstantial evidence exists that extended mask use may be related to current observations of stillbirths and to reduced verbal motor and overall cognitive performance in children born during the pandemic,” the article said. “A need exists to reconsider mask mandates.”

The article’s lead author, Kai Kisielinski, who describes himself as an independent researcher, has authored other papers in which he argues that mask wearing might cause significant health problems. He did not reply to our emails.

Experts told us the article is flawed.

Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, said the review article relied partly on studies of animals that are chronically exposed to carbon dioxide.

Those studies are not applicable to humans intermittently wearing face masks, he said.

Jeremy Howard, a scientist at the University of San Francisco, said the review article overestimates by 60 times the amount of carbon dioxide people breathe when wearing masks.

When humans breathe, they inhale about 6 liters of air, but because a mask has 0.1 liters of space, 1/60th of the air breathed while wearing a mask comes from inside the mask, he said.

“I’m not aware of any research showing that mask usage causes serious health problems,” Howard added. “Many occupations require extended mask usage, so if there was such a link, we would have clearly seen it from that data.”

We’ve debunked several claims that face masks cause health problems. The false claims included that mask wearing for COVID-19 shuts down the body’s immune system; that they cause below-normal levels of blood oxygen; and that they endanger children by trapping carbon dioxide.

Scientists have found little evidence that the kind of masks worn by schoolchildren negatively affect oxygen or carbon dioxide levels. Scientists also say contamination levels on masks are no worse than contamination levels on other common objects.

Studies have not found significant health problems even from prolonged mask wearing.

Indian researchers surveyed 124 of their nation’s ear, nose and throat hospital professionals who had prolonged use of face masks. Prolonged use “causes significant discomfort, but “facemasks are essential to protect us from COVID-19,” the 2021 study concluded.

A 2020 study surveyed 343 health care professionals working on the COVID-19 front lines in New York City who wore surgical and N95 masks. Headaches and skin irritation were the primary complaints.

Similar results were found in a December 2022 study by University of Ghana researchers, who surveyed 2,136 regular and occasional mask wearers worldwide.

Our ruling

Social media posts shared a British tabloid headline about a “study” that suggested serious health problems from wearing masks to prevent COVID-19 infection.

The study reviewed other studies and cited no firm evidence linking mask wearing to stillbirths and other health risks.

Health experts disputed the article’s warnings, saying the article relied partly on irrelevant animal studies and overstated how much carbon dioxide is breathed while mask wearing.

The claim has an element of truth in that the article issued a warning about mask wearing. But it leaves a misleading impression about the article’s findings and how they should be weighed against other evidence that shows sustained mask usage is safe.

We rate the claim Mostly False.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.