No Link Between Face Masks and CO2 Poisoning, Even in People With COPD, Study Finds

The use of face masks does not cause intoxication induced by exhaled carbon dioxide (CO2), even in people with lung function impairment such as those with chronic obstructive pulmonary disease (COPD), a study reports.

The study, “Effect of Face Masks on Gas Exchange in Healthy Persons and Patients with COPD,” was published in the Annals of the American Thoracic Society.

During the COVID-19 pandemic, the use of masks by the public to mitigate disease transmission has become a subject of deep political discussion. Inconsistent recommendations by authorities have raised controversy and led to a divided public opinion, according to the authors.

Some people argue that wearing face masks poses safety concerns, as the users rebreathe their exhaled CO2 and hypoxemia (low blood oxygen levels) might be induced.

To shed some light on this matter, a team from the University of Miami Miller School of Medicine conducted a study to determine whether the use of surgical masks contribute to gas exchange abnormalities in people, both with and without lung issues.

Changes in CO2 and oxygen levels were measured in 15 healthy individuals (average age of 31.1 years) and 15 veterans with severe COPD (average age of 71.6 years old), before and while using surgical masks.

“We did not intend to compare healthy versus diseased individuals but to assess the effect of using a surgical mask in two distinct populations,” the researchers wrote. “We focused in severe COPD subjects as they are at a higher risk of CO2 retention compared with subjects of milder severity or other pulmonary conditions.”

Participants were enrolled in the study during a scheduled six-minute walk test (6MWT) ordered to assess the need for supplemental oxygen. The test was done with individuals wearing a surgical mask. Blood sample collection was performed before and immediately after the walk test.

No significant changes in CO2 and oxygen levels were observed after wearing the mask at rest for five and 30 minutes, both in healthy people and those with COPD.

“We show that the effects are minimal at most even in people with very severe lung impairment,” Michael Campos, MD, senior author of the study, said in a press release.

After the 6MWT, oxygen levels in people with severe COPD were found to be decreased, but researchers did not consider it a major change.

“As a group, subjects with COPD did not exhibit major physiologic changes in gas exchange measurements after the 6-minute walk test using a surgical mask, particularly in CO2 retention,” they wrote.

Despite the small number of participants involved in this study, the researchers stressed that their study offers evidence that there is very little effect on gas exchange while wearing a face mask.

The team highlighted the importance of wearing a face mask to prevent COVID-19 spread, despite the discomfort its use may cause.

“It is important to inform the public that the discomfort associated with mask use should not lead to unsubstantiated safety concerns as this may attenuate the application of a practice proven to improve public health,” they wrote. “Universal mask use needs to be vigorously enforced in community settings.”

Campos emphasized that patients with lung diseases, in particular, should wear a face mask, along with hand-washing and social distancing to reduce the risk of infection.

According to Campos, the breathlessness that some people may feel during mask use “likely occurs from restriction of air flow with the mask in particular when higher ventilation is needed (on exertion). An overly tight mask may also increase the feeling of breathlessness. The solution is simply to slow down or remove the mask if you are at a safe distance from other people.”

The team believes that these new data “will help mitigate fears about the health risks of surgical mask use and improve public confidence for more widespread acceptance and use.”