evidence: Health authorities like the World Health Organization and the U.S. Centers for Disease Control and Prevention now recommend that the public use face masks in shared spaces, like public transportation and grocery stores. This change in guidance occurred after several studies found that infected individuals can transmit COVID-19 even when not showing symptoms. Contrary to many viral claims, face masks do not cause oxygen deficiency or a toxic buildup of carbon dioxide. It is important to remember that cloth face masks, surgical masks, and even N95 respirators do not provide 100% protection from the novel coronavirus and therefore must be combined with other transmission control measures such as physical distancing and good hand hygiene.