Ordinary face masks are not harmful

4th Aug 2020

Claim

Wearing a mask can cause hypercapnia, by making you breathe in too much carbon dioxide.

Conclusion

This is not true. Wearing a mask is safe for most people. There may be rare instances of harm involving tight-fitting N95 or FFP2 masks.

We’ve seen posts on Facebook claiming or implying that face masks can be harmful, because they force the wearer to breathe in too much carbon dioxide. 

For most masks and face coverings, as we have mentioned before, this is not true. (In rare cases, it might be correct for certain medical respirators, known as N95 masks in the US and FFP2 masks here in the UK.)

We’ve written elsewhere about the evidence on whether masks reduce the chance of spreading or contracting Covid-19

The evidence 

The Facebook posts describe people inhaling too much carbon dioxide (causing a condition called hypercapnia), supposedly as a result of wearing masks.

“[The claim that wearing masks can give someone] hypercapnia is malicious misinformation,” says Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases at the University of Nottingham. “Surgeons wear masks for hours doing some operations.”

Paul Hunter, Professor in Medicine at the University of East Anglia, conducted a review of the evidence on mask-wearing in April. He told Full Fact: “We spent some time looking for evidence of harm.”

“There are studies that show, with an N95 mask, some people have an elevated blood carbon dioxide level, and some also reduced oxygen level, so there is an element in truth in that. That does not apply to ordinary surgical masks, and it sure as heck doesn’t apply to other types of face covering.”