Claims that wearing a face covering contributes to carbon dioxide poisoning have been debunked by scientists.
New research shows face masks are unlikely to cause overexposure to CO2, even in patients with lung disease.
Scientists urged that the public "should not believe that masks kill."
During the Covid-19 pandemic, the face mask debate has become a highly political issue with protestors rallying worldwide against wearing them.
Some anti-mask protestors have falsely claimed they put people's health at risk by trapping CO2.
But the new findings have shot holes in such statements and scientists maintain that face masks are key to preventing the spread of coronavirus.
Dr Michael Campos, from the University of Miami, USA, said: "We show that the effects are minimal at most even in people with very severe lung impairment."
He added: "The public should not believe that masks kill."
In the study, researchers assessed problems with changes in oxygen level or carbon dioxide levels in people before and while using surgical masks.
Participants included both healthy individuals and veterans with chronic obstructive pulmonary disease (COPD) who "must work harder to breath" according to the ATS Patient Education Fact Sheet on the disease.
From his research, Dr Campos explained the feeling of breathlessness that some healthy people may experience.
He said: "Dyspnea, the feeling of shortness of breath, felt with masks by some is not synonymous of alterations in gas exchange.
"It likely occurs from restriction of air flow with the mask in particular when higher ventilation is needed (on exertion).
"If you're walking briskly up an incline, for example, you may experience feelings of breathlessness.
"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."
Dr Campos stressed the importance of wearing a face mask to prevent COVID-19 infection.
He added: "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."
If a surgical mask is not available, a cloth mask with at least two layers is recommended by the Centers for Disease for Control and Prevention (CDC).
Patients with lung disease, in particular, should avoid getting infected and should wear a face mask which is proven to reduce the risk of COVID-19 infection along with hand washing and social distancing
The study was partly prompted by reports of a public hearing in Florida where individuals made inflammatory comments, namely that wearing masks were putting lives at risk and finding out that no data on the effects of surgical masks on gas exchange was available.
Dr Campos added: "We acknowledge that our observations may be limited by sample size, however our population offers a clear signal on the nil effect of surgical masks on relevant physiological changes in gas exchange under routine circumstances - prolonged rest, brief walking."
The findings were published in the journal Annals of American Thoracic Society.