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Canada's chief public health officer recently released updated recommendations for non-medical masks. Meanwhile winter is approaching. That's led CBC readers to send us new, more detailed and more seasonal questions about wearing masks to protect against the spread of COVID-19. We checked in with experts for the answers. (You can also check out our previous mask FAQs, including questions such as: Is heat needed to clean reusable masks? Can I use a mouth shield instead of a mask? And can I reuse disposable masks?)

In early November, Canada's Chief Public Health Officer Dr. Theresa Tam updated recommendations for non-medical masks. She now recommends that masks be at least three layers instead of two, and that the third layer be a filter-type fabric, such as non-woven polypropylene fabric. However, she said you don't need to throw out your two-layer masks.

Health Canada has instructions for making masks with three layers, and says you can find non-woven polypropylene as:

In some reusable shopping bags. 

Non-woven polypropylene is used in both N95 and medical masks. It shouldn't shed fibres, says James Scott, professor and head of the occupational and environmental health division at the Dalla Lana School of Public Health at the University of Toronto.

Even if it did shed, he estimates that the allowable exposure to such fibres is "higher than I would ever expect from a shedding mask."

He added that N95 masks can be reused up to 10 times when they are cleaned between uses with gentle hydrogen peroxide without damaging the filter material. However, he doesn't know how durable non-woven polypropylene is after repeated laundering at home.

Meanwhile, so many other things in our homes are made of synthetic materials that you're probably already breathing in lots of polypropylene fibres in the dust around you anyway. A 2016 study from French researchers found that 33 per cent of fibres found in indoor air were synthetic and that polypropylene was the predominant material.

However, there are a few reports of lung problems potentially linked to synthetic fibres among textile workers exposed to very high levels.

According to the Competition Bureau of Canada, labelling laws for clothing also apply to non-medical masks. That means masks sold commercially must have a removable label such as a sticker, hang tag, wrapper or a permanent label that includes:

The fibre composition in percentages.

The seller's name and principal place of business (full postal address) or a registered CA Identification Number.

The Competition Bureau of Canada says the labelling rules apply to businesses and artisans alike, but not individuals who make masks to give or donate to friends, family or charity.

However, it has previously acknowledged that because such masks are new to the marketplace, those who make them may not yet understand the rules.

If you think a vendor is making false or misleading claims about their products, you can report that to the bureau using this online form.

Yes, distancing is still required, as regular medical and non-medical masks only reduce the number of particles from your nose and mouth. They don't eliminate them, says Dr. Anand Kumar, associate professor of medicine at the University of Manitoba in Winnipeg. (Respirator masks such as N95s do a much better job of filtering particles.)

While most masks reduce particle spread by about 80 per cent, "that leaves 20 per cent of particles still going out. How far? Nobody really knows," he told CBC News.

But the greater the distance, the greater the protection, whether you're wearing a mask or not. Doubling the distance between you and another person reduces the viral particles reaching you about eightfold, Kumar said. And wearing a mask should cause the larger, most-infectious particles to drop close to an infected mask wearer before they can reach another person.

So, how close can you get if you're both wearing masks?

There's no definite answer, says Martin Fischer, an associate professor of chemistry at Duke University in Durham, N.C., who has studied how to measure the effectiveness of different masks. That's because the risks depend on so many factors, such as how well the masks worn by each person stop particles and how long you interact.

Kumar and other experts note that approaches such as masking and distancing should be thought of as "layers" of protection that are "worn" together and aren't replacements for one another.

"It's not one or the other ... it's as many as you can do that gives you maximum protection."

Ian Mackay, an Australian virologist, illustrates this using the analogy of Swiss cheese — the virus can make it through the holes in some slices, but if you have many layers, it won't get through the whole block of cheese.

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That's probably not a good idea.

Canada's chief public health officer has advised Canadians to skip kissing and wear a mask when getting intimate with a new partner to protect yourself from the coronavirus.

If you lean in very close — like you would for a kiss — you could unintentionally exchange droplets from breath around the sides of a mask, explained Colin Furness, an infection control epidemiologist at the University of Toronto, which could lead to transmission of the virus. 

With many parts of the country experiencing increased community transmission, Sumon Chakrabarti, an infectious disease physician with Trillium Health Partners in Mississauga, Ont., said it is best to follow local public health guidelines, which include minimizing close contact with people outside your immediate household.

WATCH | Doctors answer questions about what activities and places are higher risk for COVID-19:

It depends on the mask.

There are two main categories of masks:

Respirators such as N95s, which do protect the wearer and are therefore worn by medical staff who treat COVID-19 patients. 

Regular surgical or non-medical masks, which are designed mainly to stop particles exhaled from your nose or mouth from getting too far from you.

Studies show that those regular masks are very good at filtering particles leaving the mouth and nose of the wearer, as they tend to block larger particles more effectively. That's how they protect the people around you if you're infected.

But yes, there is some evidence that they can protect the wearer, too, including a metanalysis of 172 previous studies published this spring.

Lab experiments suggest they can block roughly 80 per cent of viral particles from entering your nose and mouth, and that can reduce the dose and therefore the severity of COVID-19 infection if you do become infected. 

There's even better evidence that when most people wear masks, everyone is protected. 

"We're seeing, as we put all the data together, that masks can be broadly helpful in reducing transmission from person to person outside of health-care settings and even just in the general community," said Dr. Suzy Hota, medical director for infection prevention and control at the University Health Network in Toronto.

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That depends on whether you're breathing, talking, sneezing or coughing. Shouting, cheering and singing all produce more droplets than breathing or talking, and those particles come mainly out your mouth. And coughing, mainly from your mouth, can propel droplets more than two metres.

But sneezing can propel particles, mainly from your nose, up to eight metres, studies show.

On the other hand, it's not just the quantity of droplets that matters but also how infectious they are. Studies of COVID-19 patients have found higher amounts of virus in the nose than in the throat.

WATCH | Can I leave my mask under my chin when not using it?

No. Wearing a mask below your nose defeats its purpose.

That's because masks and face coverings are supposed to reduce coronavirus-spreading respiratory droplets, and the virus can both exit (see previous question) and enter via your nose.

In places where masks are mandatory, policies usually specify that they need to cover your nose. For example, Quebec's regulation says a mask needs to cover the nose and mouth while Ontario's says it needs to cover the mouth, nose and chin.

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Generally, yes, they're permitted as face coverings under mandatory mask bylaws as long as they cover the required parts of your face (see previous question). However, you should check your local region's guidelines, as this isn't the case everywhere. For example, Quebec's health ministry told CBC News in an email that it requires face coverings to be properly fitted to your face and have at least two layers, so loose scarves or neck warmers are not acceptable. 

Newfoundland and Labrador's health ministry notes that scarves and other cloth face coverings may be less effective than non-medical masks. Quebec's health ministry warns that droplets could pass through the openings in a loose scarf.

Fischer's study in September showed that many scarves, balaclavas, bandanas, neck fleeces and neck gaiters are not very effective at blocking respiratory droplets compared to masks as they're too thin or porous. In fact, some neck fleeces and neck gaiters tend to break large droplets into smaller ones, creating more particles that stayed airborne longer and potentially increasing viral transmission.

Scarves and neck warmers also generally don't meet the recommendations that the Public Health Agency of Canada has for face coverings, such as fitting securely to the head with ties or ear loops and being made of at least two layers of tightly woven material fabric, such as cotton or linen. 

Toronto Public Health recommends that when wearing a face covering that doesn't cover the mouth, nose or chin without gaps a face mask should be worn underneath.

WATCH | Are you making these face mask mistakes?

Multiple experts we talked to said it's not really known whether masks are less effective when damp or frozen.

However, when it comes to N95 masks, the electrostatic filter stops functioning if it gets soaking wet, says Dr. Allison McGeer, infectious diseases specialist at Toronto's Mount Sinai Hospital.

Regardless of whether filtering abilities are affected, damp or frozen masks tend to be more difficult to breathe through, notes Conor Ruzycki, a University of Alberta doctoral candidate in Edmonton who has done research on the filtration abilities of homemade masks. 

Wet masks can also provide an environment for bacteria to grow, he and other experts said.

"For these reasons, it's a good idea to replace a wet or frozen mask with a fresh and dry one," added Ruzycki, who volunteers with Masks4Canada, a group that advocates for mandatory mask laws.

"With winter coming, consider carrying an extra mask or two to change into if you find your mask freezing up or becoming water-logged."

WATCH | How to wear and care for masks:

Yes, if they're clean.

"Sharing masks is not risky if they are well washed," said Furness. Health Canada recommends washing them on a hot cycle and then drying thoroughly.

But even with good laundering, Dr. Sumon Chakrabarti noted that masks are pretty intimate items to be swapping with others.

"Think about it like sharing well-washed underwear," Chakrabarti said. "Safe, yes. Gross, also yes."

As masks are so widely available now, he said it's a better option to use your own. 

That's unlikely if you keep your masks clean and change them as needed, experts say.

But if you allow them to get damp and don't change or clean them, then wear them for a long time, bacteria can grow in them (but not viruses, which can't reproduce outside the body.) 

That can cause masks to get smelly but wouldn't necessarily be harmful, says Kumar.

However, Furness has previously said that studies have found that wearing the same mask all day can lead to an increase in respiratory infections.

In general, public health officials recommend changing masks when they become damp or dirty.

Some CBC readers have also written in worrying that wearing masks could reduce oxygen levels or cause a buildup of carbon dioxide, but experts say there's no evidence that they can do that.

WATCH | Masks and oxygen levels:

It's not so straightforward. Cara Zwibel, a lawyer for the Canadian Civil Liberties Association, says that an argument could be made under freedom of expression.

"Like with any piece of clothing, there's this argument that people use what they wear and their appearance to express who they are," said Zwibel.

But when it comes to charter rights, the government can restrict them if they do so in a way that is reasonable and justified.

"Given the circumstances of the pandemic and the importance of the objective of curbing the spread of COVID-19, a mere preference not to wear a mask likely would not be protected," said Joanna Baron, executive director of the Canadian Constitution Foundation in Calgary. a non-profit organization that argues charter cases in court.

For someone who says they are unable to wear a mask for medical reasons, Zwibel says, it depends on the situation, but a case could be made under equality rights.

"If someone was treated differently or couldn't access a government service because of a medical issue that precluded them from wearing a mask, then there would be a potential equality issue."

First, you should approach the customer and ask if they have a medical reason for not being able to wear a mask. If they say they do, you'll have to take their word for it.

"A mere statement by an individual that they qualify for an exemption from a mandatory mask order is sufficient. They do not need to produce medical proof," Baron said.

The Ontario Human Rights Commission recommends everyone involved should be flexible in the situation and explore whether individual accommodation would suffice.

What that accommodation might look like would vary based on the type of business or service, the medical reason precluding the customer from wearing a mask and the current government directives during the pandemic. It could be something as simple as a curbside pickup arrangement.

WATCH | How to stay safe from COVID-19 on a plane:

For any setting, including an airplane, the Public Health Agency of Canada recommends any mask that covers the nose and mouth, can be secured to the head comfortably, allows for easy breathing and does not require frequent adjustment.

According to the Canadian Air Transport Security Authority website passengers must wear coverings that are properly secured and cover the mouth and nose and are made of at least two layers of tightly woven fabric, such as cotton or linen, which most on the market are.

Here's what types of face coverings you don't want to show up to the airport with:

A face shield without a proper mask underneath.

A mask with an exhalation valve or vent.

Militaristic masks such as gas masks.

Face coverings that cover the entire face. 

Ruzycki says properly fitted N95 respirators do provide more protection against airborne particles than regular cloth or surgical masks, but he doesn't recommend them because the risk of COVID-19 transmission on an airplane is relatively low where everyone is wearing masks and there is a shortage of N95 masks.

"Until we can guarantee that health care and frontline workers who face constant exposure to SARS-CoV-2 have regular and consistent access to N95 respirators, it's a good idea for the public to use well-designed and well-fitted cloth and surgical masks."

Some studies have also shown that N95 masks are uncomfortable when worn for long periods of time, he said, especially if you're not used to them.

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