QUESTION: Why do the public health authorities keep telling us to always wear a mask? I have not seen any information showing that masks stop the spread.
Instead, most of the info I have read says cloth masks do not block small aerosol particles. But they cut needed oxygen intake and raise CO2 intake.
ANSWER: Masks do not provide 100% protection, but they are much better than nothing. The Centers for Disease Control and Prevention reported an accidental experiment in which two hairstylists in Springfield, Mo., developed symptoms of COVID-19 (MMWR, July 17, 2020). Both continued to cut hair while wearing masks. They interacted with 139 clients who also wore masks. None of the clients who were tested came down with COVID-19.
In addition, a study in a large Massachusetts hospital system found that when patients and staff all wore masks, the rates of COVID-19 infection dropped dramatically (JAMA, July 14, 2020). In commenting on this research, public health experts point out that face masks serve two purposes: They protect the wearer against inhaling droplets and even some aerosol particles. They also trap particles being exhaled by infected individuals (JAMA, July 14, 2020). As a result, universal masking can help cut transmission.
As for oxygen and CO2, a recent study found that face masks do not reduce oxygen nor lead to carbon dioxide buildup (Annals of the American Thoracic Society, Oct. 2, 2020). This held not only for healthy volunteers, but also for those with COPD, which makes it much harder for people to breathe.