Toronto Public Health states:
Wearing masks/face coverings can be an added public health measure for containing the spread of COVID-19 when it is used in combination with frequent handwashing, physical distancing and staying home when sick.
The risk of spreading COVID-19 is greater indoors as there is less air flow and ventilation, more crowding, and a greater chance of touching surfaces that have been contaminated by respiratory droplets.
Wearing masks or face coverings indoors helps us keep our respiratory droplets to ourselves to prevent spreading germs to others. There is also evidence that cloth masks can reduce the spread of respiratory droplets into the air and landing on surfaces. Jurisdictions that have legislated mandatory masks have seen a decrease in new COVID-19 cases.