For months it has been clear that wearing a face mask reduces the transmission of Covid-19, because it prevents your respiratory droplets from spreading and potentially infecting other people. Now the Centers for Disease Control has highlighted another benefit of mask-wearing that many hoped or suspected was the case: Masks can also protect the wearer from other people's droplets, the CDC wrote in a scientific brief published Tuesday.
Wearing a mask is "a two-way street," Dr. Anthony Fauci told MSNBC's Andrea Mitchell in an interview Tuesday, citing new research on personal protection from mask-wearing.
Masks made with multiple cloth layers have been shown to prevent 50-70% of a person's respiratory droplets from spreading to others (which is one of the main ways the virus infects others, when a contagious person sneezes, coughs, breathes or talks).
On the other hand, wearing a cloth mask can also reduce the amount of infectious droplets you personally are exposed, because the fabric barrier filters out a degree of particles, according to the CDC. Some data has shown that a multi-layer cloth mask made from a fabric with a high thread could filter out nearly 50% of respiratory droplets and aerosolized particles. (N-95 respirators that are used by healthcare professionals can filter out 95% of very small particles.)
Ideally, if everyone — infected or not — wears a mask the efficacy is even higher.
More research needs to be done to determine which materials and what type of fit would boost a mask's filtration benefits. (A study out of Duke University showed that surgical face masks made from a plastic-derived material called polypropylene are the most effective at filtering out particles, followed by masks made from two layers of cotton and one layer of synthetic material.) The CDC currently recommends that people choose masks that are made from two layers of breathable, washable and tightly woven fabric.
Epidemiological studies have shown that when everyone wears a mask, the risk of transmission goes down. For example, a Beijing study of 124 households with at least one confirmed case of Covid-19 found that when the infected person and the other members of the household all wore masks it reduced the spread by 79%.
The CDC says that a combination of "universal masking policies," social distancing, ventilation and hand hygiene could prevent future lockdowns.