Some communities across Canada have started making non-medical face masks mandatory on public transit — or even in businesses or indoor spaces — to curb the spread of COVID-19.

Some doctors and epidemiologists are calling for such laws to be more widespread. But others warn about the potential negative impacts and say the scientific evidence isn't strong enough to warrant such heavy-handed measures. Here's a closer look at the issue. 

What are current public health recommendations around masks for healthy people in public?

The Public Health Agency of Canada recommends wearing a non-medical mask or face covering in public places, especially crowded ones, when physical distancing — keeping a distance of two metres from other people — isn't possible to do consistently. Such places include stores, shopping areas and public transportation.

The idea is that masks can reduce the spread of respiratory droplets you produce when breathing, talking, coughing or sneezing. The recommendation was put in place because of growing evidence that people can transmit COVID-19 through such droplets before showing symptoms.

Of course, people with symptoms should stay home and not be in public places.

Why do some advocates think voluntary recommendations aren't good enough?

A national group of health-care professionals and epidemiologists called Masks4Canada and a group in Quebec have recently called for more laws making masks mandatory in certain circumstances.

Masks4Canada has written an open letter to federal health officials asking them to recommend such laws to lower levels of government for:

  • All indoor spaces outside the home, such as schools, libraries, community centres, stores and restaurants.
  • Crowded areas, both indoors and outdoors, including protests and busy parks or trails.
  • Public transit.

The letter noted that despite recommendations, a recent poll showed less than half of Canadians are wearing masks when they go out in public. It cited computer simulation studies that showed more than 70 per cent of the population needs to wear masks in public to significantly reduce transmission.

It said that the widespread adoption of other public health measures, such as seat belts and bike helmets, have required laws.

Dr. Amy Tan, an associate professor of family medicine at the University of Calgary and a member of the group, said the goal is to make wearing a mask a universal expectation — "the mindset of 'no mask, no boarding' [on transit] or at a store, 'No mask, no service' — similar to 'no shirt, no service.'"

Some businesses, such as the Longo's grocery store chain, have already implemented policies barring customers without masks. 

Tan said laws help increase mask use by giving businesses and transit "cover to say, 'We need to do this.'"

How good is the evidence that mandatory mask laws reduce transmission?

A recent study by a German non-profit economic think-tank compared regions in Germany that implemented mandatory mask laws at different times (before the entire country made masks mandatory in stores and transit on April 27). The study, which was published on the group's website but not in a peer-reviewed journal, suggested mask laws could reduce the daily growth rate of reported infections by 40 per cent.

Other studies show that masks do reduce the rate at which sick people shed the virus and the distance droplets travel from your mouth. Mathematical modelling studies also suggest that universal mask wearing can be used to control epidemics.

Advocates of universal mask wearing note that countries with widespread or mandated mask use, such as South Korea, Taiwan, China and the Czech Republic, have seen reduced cases and fatalities, although that may be due to other factors.