evidence: Face masks do not cause carbon dioxide poisoning—During the COVID-19 pandemic, some individuals suggested that wearing face masks could cause health risks, especially for people with chronic obstructive pulmonary disease (COPD), a group of diseases that cause breathing problems. In 2020, researchers at the Miami VA Healthcare System and the University of Miami studied 30 people, 15 with lung conditions and 15 without, to determine whether wearing a surgical face mask would change levels of oxygen and carbon dioxide saturation in the blood. For both groups they found there were no significant changes in oxygen and carbon dioxide measurements after a walking test, even in subjects with severe lung impairments. [...] Effect of face masks on gas exchange in healthy persons and patients with COPD. Samannan R, Holt G, Calderon-Candelario R, Mirsaeidi M, Campos M. The effects of wearing face masks on gas exchange are minimal at most even in people with very severe lung impairment. Ann Am Thorac Soc. 2021 Mar;18(3):541-544.