Does wearing a medical/surgical mask or cloth face covering cause unsafe oxygen levels or harmful carbon dioxide levels to the wearer?

No. Medical masks, including surgical masks, are routinely worn by healthcare workers throughout the day as part of their personal protective equipment ensembles and do not compromise their oxygen levels or cause carbon dioxide buildup. They are designed to be breathed through and can protect against respiratory droplets, which are typically much larger than tiny carbon dioxide particles. Consequently, most carbon dioxide particles will either go through the mask or escape along the mask’s loose-fitting perimeter. Some carbon dioxide might collect between the mask and the wearer’s face, but not at unsafe levels.

Like medical masks, cloth face coverings are loose-fitting with no seal and are designed to be breathed through. Workers may easily remove their medical masks or cloth face coverings periodically (and when not in close proximity with others) to eliminate any negligible buildup of carbon dioxide that might occur. Cloth face coverings and medical masks can help prevent the spread of potentially infectious respiratory droplets from the wearer to their co-workers, including when the wearer has COVID-19 and does not know it.