On May 21st, the New England Journal of Medicine published an article titled Universal Masking in Hospitals in the Covid-19 Era, which states:
We know that wearing a mask outside health care facilities offers little, if any, protection from infection.
And as recently as last week, Dr April Baller of World Health Organization said:
“If you do not have any respiratory symptoms such as fever, cough or runny nose, you do not need to wear a mask,”
The common counter-argument to this point is that masks don’t prevent you from getting sick, but rather prevent you from spreading it if you’re infected.
However that is disputed by a paper published just last month, but based on research conducted in late 2019 (before the Covid outbreak),
which found that [my emphasis]:
Disposable medical masks are loose-fitting devices that were designed to be worn by medical personnel to protect accidental contamination of patient wounds, and to protect the wearer against splashes or sprays of bodily fluids. There is limited evidence for their effectiveness in preventing influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure. Our systematic review found no significant effect of face masks on transmission of laboratory-confirmed influenza.
In fact, not only is there substantial evidence masks will not prevent you getting sick, there is some evidence they could actually be counter-productive.
A trial of cloth masks in 2015 found that:
Moisture retention, reuse of cloth masks and poor filtration may result in an increased risk of infection.
Hellbound and Down 