Do masks reduce your oxygen levels? Your COVID-19 questions answered

We're answering your questions about the pandemic. Send yours to and we’ll answer as many as we can. We’ll publish a selection of answers every weekday online, and also put some questions to the experts during The National and on CBC News Network.

From mask types to second waves, here's what you're asking us today

More and more places are mandating that people wear masks in public in an effort to curb the spread of the coronavirus that causes COVID-19. But many Canadians are concerned wearing masks will have a negative impact on their health. Experts say it won't. (Lynne Sladky/The Associated Press)

The information in this article was current at the time of publishing, but guidelines and advice can change quickly. Check with your local public health unit for the most-current guidance, and find the latest COVID-19 news on our website.

We're breaking down what you need to know about the pandemic. Send us your questions via email at and we'll answer as many as we can. We'll publish a selection of answers every weekday on our website, and we're also putting some of your questions to the experts on the air during The National and on CBC News Network. So far we've received more than 48,000 emails from all corners of the country.

Do masks reduce your oxygen levels?

From big cities to small towns — and the entire province of Quebec — more and more places in Canada are making masks mandatory in indoor public spaces to help curb the spread of the coronavirus that causes COVID-19. 

The new rules have sparked some challenges, including from anti-mask groups and people spreading misinformation about mask-wearing. That's confused some Canadians who are left wondering if there's any truth behind some of the claims. Sharon P., for example, is concerned a mask might reduce one's oxygen levels.

The experts we spoke to said there's no truth to that claim.

"I haven't seen any medical or scientific evidence that shows that wearing a mask depletes your body of oxygen," said Dr. Susy Hota, medical director of infection prevention and control at Toronto's University Health Network.

Nor do they let any harmful gases, such as carbon dioxide, build up, she said. 

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So, you may feel hot or become more aware of your breathing, but "it's not dangerous," she said.

Dr. Jennifer Kwan, a family physician in Burlington, Ont., agreed. 

Oxygen and carbon dioxide still get through your mask, but it catches the droplets that contain the virus, "which is what helps reduce transmission," she said.

"As a medical professional, we wear masks in our day-to-day practice and it has not caused doctors or nurses or surgeons any harm."

The real risk, said Kwan, is wearing your mask incorrectly, including sharing it with others, reusing non-reusable masks, or not cleaning cloth masks properly.

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"It's very important with the increase in mask-wearing to also be teaching people to wear them properly," she said. 

That includes:

  • Washing or sanitizing your hands before putting it on and taking it off.
  • Handling it by the ear straps only. Don't touch the front.
  • Keeping your face covered from above your nostrils to below your chin. 

We addressed more frequently asked mask questions, including the best kinds of fabrics, filters and whether facial hair poses a problem, in a previous FAQ.

Is it safe to wear masks with vents?

You may be seeing people on the street with masks that have valves or vents designed to make breathing easier. 

Jill F. is wondering if these masks are effective at stopping the spread of the coronavirus.

The answer is no. 

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A vented mask may look high-tech and be more comfortable to wear, but Health Canada says they allow infectious respiratory droplets to get through and has asked Canadians not to use them for preventing the spread of the coronavirus.

"The benefit that we see from masks is often protecting others from you," explained infectious diseases specialist Dr. Sumon Chakrabarti.

"So if you have a vent there and you have COVID-19 … you'll be expelling those particles, so it defeats the purpose of the mask."

There are some masks that look like they have a valve, but instead it's just a plastic piece sitting on top of the fabric. Kwan says these fake vents are just for "esthetic purposes" and don't compromise the mask's function, so long as there is fabric behind it.

So skip the vented and valved masks. Both Chakrabarti and Kwan recommend surgical or homemade masks instead.

And remember: wearing a mask alone will not prevent the spread of COVID-19; it's not a substitute for physical distancing and good hand hygiene.

Where are we in the pandemic?

Many provinces loosened restrictions after the number of COVID-19 cases began to decline but are now seeing a resurgence. That has many Canadians, including Tom L., wondering what stage of the pandemic we are in. 

The country is still technically in the first wave, experts say.

In order for the first wave to end, we'd have to reach a point where we see "essentially zero" new cases, explained Dr. Christopher Labos, an epidemiologist, cardiologist, and associate in the Office for Science and Society at McGill University. Any influx that follows would signal the start of a potential second wave. 

That means a second wave is not the same as a second peak. 

"[A second wave] has to be differentiated from a second peak, which is within the first wave when the cases can go up and down — and go up again," Labos said.

Despite significant decreases, Ontario and Quebec haven't been able to get rid of the virus entirely, and Alberta is seeing an uptick.

"If the number of cases starts to go up again ... it technically wouldn't be a second wave, it'd be a second peak within the first wave because we never had cases go down to the zero mark," Labos said. 

Whether Canada will see a second wave isn't a certainty. Some experts say it's preventable, as long we stay on top of the smaller outbreaks that will arise in the near future. 

"If we jump on it quickly and we have the capacity to do the early identifications, contact tracing and isolation, we can get through this without a big second wave," said Dr. Isaac Bogoch, an infectious disease physician and scientist with Toronto General Hospital.

"But if we don't, if we let our guard down, well, here it comes."

Last week we answered questions about getting your nails done.

Keep your questions coming by emailing us at


With files from Adam Miller