evidence: Oxygen is 0.120 nanometers, and carbon dioxide is 0.232 nanometers.Respiratory droplets are typically 5000 to 10,000 nanometers in diameter.The filtration pores in a cloth mask are typically between 10 nanometers and 6000 nanometers. Put simply, "math and physics" verify that face masks cannot stop the flow of respiratory gases, but they can stop respiratory droplets, Poston says. Can I Just Cover My Mouth With a Mask? In short, absolutely not, says Poston. In order to help prevent the spread of COVID-19, you cover your mouth and nose. Consider a recent study in Nature Medicine, which showed that mucus-producing cells in the nose had the highest levels of COVID-19 proteins, further emphasizing why it’s necessary for your face to be covered from the bridge of your nose to your chin. WHO: Fabric Face Masks Should Have 3 Layers And as for the rumor that wearing a mask can cause a weakened immune system, it’s just not the case, Poston says. "Your immune system is exposed to pathogens of all sorts throughout your lifetime," she says. "Wearing a mask to decrease exposure to respiratory pathogens will not have a significant impact on the function of your immune system.