TORONTO -- Face masks are now a regular sight on the streets of Canadian cities, and come in all shapes, sizes and styles, from disposable surgical masks to brightly patterned cloth masks.

But not all masks provide the same level of protection to the wearer and those around them. Increasingly, health officials, countries, cities and airlines are recommending against masks with an exhaust valve -- or outright banning them.

You’ve likely seen these masks before: they look like any ordinary face covering, but have the addition of a raised plastic valve, around the size of a quarter, and usually set into one half of the mask.

The valve itself can be called a respirator valve, exhalation valve or exhaust valve. Some N95s -- which are normally very effective masks -- even have these valves.

But according to Health Canada’s website, wearing masks with a valve will do little to prevent the spread of COVID-19.

“Some commercially available respirators have exhaust valves which are intended to make the respirator more comfortable for the person wearing it, but also allow infectious respiratory droplets to be released outside the respirator,” the health agency writes.

“Use of respirators with exhaust valves will not protect others from COVID-19. Please do not use respirators with exhalation valves.”

The goal of the valve on these masks is to allow the user to breathe out more comfortably. The concept is that on an outward breath, the valve opens to allow the exhalation to escape and prevent the buildup of heat and bacteria on the inside of the mask.

This is great when you’re wearing a mask to protect you from inhaling dust while doing some DIY renovation of your kitchen.

Not so great when you’re wearing the mask because of a global pandemic, where anyone’s breath might be carrying COVID-19 -- including yours.

Health officials have emphasized numerous times that the main purpose of wearing face masks is to protect others from you, not the other way around. Wearing a face mask may provide the wearer with more protection from contracting the virus than not wearing one, but its main goal is to cut down on droplets expelled from a person’s mouth when they breathe, sneeze or cough.

Droplets sprayed from a person infected with COVID-19 is the main way the virus spreads, according to health experts. And people can spread the virus even if they’re asymptomatic, or before they exhibit symptoms.

This means that a valve that allows your exhalation to pass through without being filtered through the mask material itself can also be allowing more of those potentially dangerous droplets to escape into the air.

Dr. Rhonda Low, a Vancouver-based family physician, explained to CTV Morning Live in late May that these masks could even make an exhalation more dangerous than without a mask.

“If you're sick, you're forcibly exhaling droplets through that little valve more, at a smaller aperture, which means the droplets go out quicker and could go farther,” she said.

A recent study on how to test the effectiveness of various types of masks published in the journal Science Advances found that the presence of a valve on an N95 that they tested made it significantly less effective than a fitted N95 with no valve.

“The performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow,” the study reads.

“While the valve does not compromise the protection of the wearer, it can decrease protection of persons surrounding the wearer.”

Numerous cities within Canada have put out specific recommendations telling residents to stay away from masks with valves.

A factsheet on masks put out by Toronto Public Health and revised this Wednesday specifies that masks with exhalation valves are not recommended because the valves “may filter dust particles in the air as the person inhales, but they may not filter virus particles or respiratory droplets.”

In Toronto, and in much of Ontario, face masks are mandatory in indoor areas.

Ottawa Public Health also specifies on their website that masks with exhalation valves are not recommended.

Fort Saskatchewan, Alberta, announced a plan on July 31 for mandatory face coverings to be worn in city facilities, and added that masks with an exhalation valve did not meet the standard of a face covering.

The B.C. Centre for Disease Control posted guidelines on face masks in late June, and specified that “industrial N95 respirators” were not recommended because they have valves.

The U.S. Centers for Disease Control and Prevention also recently updated their website to advise against using respirators with exhalation valves. They add that these masks also “should not be used in situations where a sterile field must be maintained” such as within a hospital setting.

Some regions aren’t stopping at just a recommendation against wearing these valved masks.

In San Francisco, California, where the wearing of face masks is required in all businesses and anytime a person comes within 6 feet of someone outside of their household, masks with valves have been included on their list of face coverings that do not comply with the regulations.

“Masks that have a one-way valve designed for easier breathing,” were listed, as well as Halloween masks and ski masks. “Holes or one-way valves allow droplets out of the mask, exposing people nearby.”

Denver, Colorado, said in a May release that any mask with a one-way valve did not count as a proper face covering under the order requiring individuals to wear masks in public.

And most airlines based in the U.S. have banned face masks with exhaust valves.

Alaska Airlines, United, Delta, JetBlue, and, most recently, American Airlines, have released mandates requiring passengers to wear proper face coverings -- specifying that masks with exhaust valves do not count.

So far, Canadian airlines such as Air Canada and WestJet have not released any specific guidance on masks with valves.