If you are infected and contagious the mask will not make you safe to be around.
Any aerosol virus you exhale will go out through your mask just as easily as it can come in, so the mask might slow the exposure a little, but it will NOT stop it.
Any aerosol virus you exhale will go out through your mask just as easily as it can come in, so the mask might slow the exposure a little, but it will NOT stop it.
Actually, I found three review papers that specifically address the question of how masks affect transmissibility of Covid-19. All of them concluded that masks inhibit transmission of Covid-19.
Also, I found another paper about the survivability of viruses in different environments. One limitation of this paper was that most of the studies were looking for viral RNA remaining in the environment, but the presence of RNA is not an indicator of infectivity. The following passage from that paper, Stability and infectivity of coronaviruses in inanimate environments leapt out at me:
Infectivity of HuCoV- 229E was undetectable after drying on aluminum, sterile latex surgical gloves, and sterile cotton gauze sponges at RT for 3 h; HuCoV OC43 survived 1 h or less[34]. Contaminated droplets will be absorbed faster on cotton materials than on fluid-repellent materials, and cotton gowns offer protection against droplets bearing viruses. Droplets or fomites that persist on a nonabsorbent disposable gown or gloves may be a risk to contaminate the environment.
SARS-CoV strain GVU6109 was isolated from a lung tissue specimen of a SARS patient during the SARS outbreak in 2003[35]; its infectivity at 10^4 tissue culture infection doses (TCID50)/mL vanished within 5 min after drying on paper or a cotton gown at RT[35], showing that the viral infectivity perished faster on the cotton gown than on an impervious surface (e.g., the disposable gown) (5 min vs 60 min at 10^4 TCID50/mL, 1 h vs 24 h at 10^5 TCID50/mL )[35].
Note: these studies used commonly circulating coronaviruses; the behavior of the Covid-19 virus should be similar.
In other words, the cotton material used in masks helps to dry (and kill) the virus quickly. This is nice to know, since I just ordered 8 yards of pure cotton cloth to use to make masks.