evidence: Contrary to viral claims, wearing surgical masks or cloth face coverings does not restrict the amount of oxygen a person breathes in, nor does it cause a dangerous buildup of carbon dioxide, according to a study published Friday in the journal Annals of the American Thoracic Society. [...] Campos and colleagues tested the effects of wearing a typical surgical mask on the body's ability to take in oxygen and exhale carbon dioxide. [...] All participants wore masks for about 30 minutes and then walked for 6 minutes, still wearing the face coverings. Using standard blood tests, researchers found no differences in levels of oxygen or carbon dioxide circulating in any of the participants' systems.