Using face masks reduces the transmission of COVID-19 and doesn’t lead to oxygen deficiency or carbon dioxide buildup in the blood
Although viruses such as SARS-CoV-2 are much smaller in size than the pores in a face mask, these viruses are carried by droplets or aerosols that can be effectively trapped by face masks, reducing aerosol emission. Face masks can’t prevent the passage of gases, so they cannot significantly reduce the amount of oxygen in the blood, nor increase the amount of carbon dioxide.