White Coat, Black Art·The Dose

How do you know if your mask is working and if the air you're breathing is safe?

With the COVID-19 variants spreading in Canada, infectious disease specialist Dr. Lynora Saxinger joins Dr. Brian Goldman to break down the newest science around masks, with tips on which ones you should be wearing and how to fit them.

Expert advice to help you level up your mask-wearing amid the spread of COVID-19 variants

Even with the more transmissible COVID-19 variants circulating, experts say a well-fitting, three-layer, high quality cloth mask can protect you just as well as a surgical mask. (Coty George/The Associated Press)

Wearing a mask is pretty common behaviour for most Canadians now, but experts say some of us have gotten a bit sloppy. 

While that might be because "everyone is so tired" of pandemic public health measures, said Dr. Lynora Saxinger, an infectious disease specialist at the University of Alberta, ensuring we're wearing masks properly is critical with cases of the more transmissible COVID-19 variants on the rise in Canada.

Health Canada currently recommends wearing a mask made of at least two layers of tightly woven fabric such as cotton, and a third layer of a filter fabric like polypropylene.

In the face of the variants, some countries like Germany have made medical-grade masks mandatory.

But Saxinger says there is data that shows "a well-performing cloth mask can work pretty much as well as a surgical mask."

Dr. Lynora Saxinger says making sure your mask fits well is key to protecting yourself. (CBC)

As the data around the transmissibility of variants is still evolving, she says, Canada's current masking guidelines don't need to change in the interim.

While Saxinger notes new data could lead to new recommendations, for now, the real challenge is making sure people follow best practices for mask-wearing.


Last week, the U.S. Centers for Disease Control and Prevention suggested double-masking based on new data.

So should you be wearing two masks? 

"My answer to that is probably a firm maybe," Saxinger told Dr. Brian Goldman, host of The Dose and White Coat, Black Art.

U.S. President Joe Biden wears two masks. The U.S. Centers for Disease Control and Prevention suggests double-masking based on new data. (AFP via Getty Images)

Whether you wear one mask or two is less important than the fit and number of layers. 

"Those are the two things to keep in mind," she said. "You might actually have a mask that has multiple layers that's well-constructed, and wearing another one would just be uncomfortable."

How to fit your mask

Saxinger says fitting your mask properly is essential for maximizing its effectiveness. 

An image shows leakage from an ill-fitting mask during CBC Marketplace’s lab test at the University of Toronto’s Dalla Lana School of Public Health. (CBC)

Here are her tips to check the fit of your mask in the mirror: 

  • When you turn your head, you shouldn't see a lot of air space between the side of the mask and your cheek. 
  • You shouldn't see a gap under the chin or under the nose piece. 
  • The nose wire should be adjusted so that it's sitting flush to the face.
  • Ensure the mask is close to your face. You can knot the mask strings or loop them before you put them over your ears, or use a mask extender around the back of your head. 

How do you know your mask is working? 

Saxinger says you don't want any air leaking out the sides, top or bottom of the mask. 

In order to check that's not happening, watch as you breathe in and out. 

Your mask should be "kind of sucking against your nose and mouth. That's actually kind of a good sign that air is flowing through the mask instead of around it as well," she said.

Check your mask for breathability. Having a proper-fitted mask ensures particles are filtered out when you breathe inward. (CBC News)

Another clear sign that your mask is not working well is if you put on glasses and they fog up a lot. 

"That means there's a lot of air coming up at the top of your mask."

Mask outdoors

While some public health officials have recommended wearing masks outdoors, Saxinger doesn't think it's necessary in most circumstances.

People wear face masks as they walk along a street in Montreal. Dr. Lynora Saxinger says, with a few exceptions, there's no need to wear a mask outside. (Graham Hughes/The Canadian Press)

"Outdoors is a much lower risk than indoors. According to the data, it's 20 times higher risk indoors than outdoors in terms of transmission risk."

One exception might be contact sports, where you can be exhaling forcefully into someone else's face, but "if you're actually just out and about outdoors on your own and you're keeping distance from others, I think a mask is unlikely to add protection for you or others."

Indoor spaces

Wearing masks in indoor settings outside of your home is mandated in many jurisdictions, but as masks don't offer complete protection, and there's currently no device that measures coronavirus in the air, some people are using carbon dioxide monitors in indoor spaces as a way of assessing risk. 


An increasingly large body of research suggests the coronavirus is airborne, and the Public Health Agency of Canada's guidelines on how COVID-19 spreads includes aerosol transmission. That means droplets can travel through the air and linger.

People exhale carbon dioxide when they breathe and it builds up in spaces that aren't well-ventilated. So higher CO2 levels in a space indicate there are more people exhaling —  and that theoretically means there could be a higher risk of coronavirus droplets in the air.

Jeffrey Siegel studies indoor air quality and is a professor in the civil and mineral engineering department at the University of Toronto. (Submitted by Jeffrey Siegel)

However, University of Toronto indoor air expert Jeffrey Siegel, cautions against "interpreting carbon dioxide as a proxy for exhaled COVID droplets."

At best, they are a blunt instrument in the tool kit against COVID, at worst, they can provide a false sense of security, he said. 

"In order to get actionable information about COVID or about anything with the indoor environment and CO2, you both really have to understand the sensor that you're using. You have to really understand the environment in which you're taking that measurement and you have to really know how to interpret it."

Still, some teachers' unions in Canada are calling for carbon dioxide sensors to be installed in classrooms, and a group calling themselves "CO2 guerrillas" in Australia measures CO2 in indoor spaces and posts them to Twitter. 

But Siegel tells people that if they have a dollar to spend, he would rather they spend it on measures that reduce the concentration of potential COVID droplets in the air — better ventilation for one — than on CO2 monitoring.

Lab tests reveal the best and worst face masks

3 years ago
Duration 2:12
Marketplace put more than two dozen consumer masks to the test to see which ones do a better job at protecting you and why.

Saxinger adds that masks remain an important public health tool, if worn properly.

Despite some slips, she says most Canadians are doing pretty well at following masking guidelines, in part because mask-wearing has become so normalized.

"It's got to the point now where if I look at a picture of unmasked people from the before times, I kind of freak out a little bit inside."

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