This story is part of Vape Fail, a CBC News series examining some of the policy failures that led to the adoption of vaping as a smoking alternative and the resulting consequences.

E-cigarette liquids currently on the Canadian market contain potentially harmful chemicals, including a suspected carcinogen banned in food in the U.S.

CBC News independently tested several nicotine vaping liquids at the Western New York Center for Research on Flavored Tobacco Products (CRoFT) in Buffalo, N.Y., last month.

The test results found two chemicals in particular, pulegone and benzaldehyde, that could be dangerous to human health when vaped at high levels.

"We tested some flavours that show high toxicity," said Maciej Goniewicz, a leading e-cigarette researcher and associate professor of oncology at the Roswell Park Comprehensive Cancer Center.

"We found some chemicals that raise concerns, particularly when it comes to inhalation."

CBC News independently tested a variety of different brands and flavours of vaping liquids and found two chemicals in particular, pulegone and benzaldehyde, that could be dangerous to human health when vaped at high levels (Craig Chivers/CBC)

Pulegone is typically found in menthol vaping products and cigarettes. It's a suspected carcinogen that was banned by the U.S. Food and Drug Administration (FDA ) as a food additive in 2018 and has also been found to cause cancer in lab animals.

The tobacco industry has phased out pulegone in cigarettes because of concerns over potential toxicity to smokers .

"This is an additive that has been banned in food products in the U.S.," Goniewicz said.

"We don't know whether it might also be the case for inhalation with electronic cigarettes, but it definitely raises concern, and we should investigate in more detail."

Potentially harmful flavouring chemicals

A spokesperson for Health Canada said it is studying the potential health effects of pulegone in vaping liquids and could take action if it is found to "pose a danger to human health or safety."

Benzaldehyde, which is typically used in cherry flavours of e-cigarette liquids, has been shown to be a potentially toxic respiratory irritant at high doses.

"We have no clue what [these chemicals] can do to your lungs," said Mathieu Morissette, a researcher at the University Institute of Cardiology and Respirology of Quebec and an associate professor at Laval University in Quebec City.

"Those flavours were meant to be eaten, not to be inhaled, and basically, that is the main question we have right now: Are they safe to inhale?"

Morissette said that from a research perspective, "it's really a huge puzzle if you want to address the question properly."

WATCH | Is secondhand vapour harmful? Is there a safe way to vape? Respirologist John Granton answers your questions:

Respirologist Dr. John Granton answers questions about vaping as a smoking alternative, health consequences and future regulations. 23:26

'We don't know what will happen with their lungs'

Health Canada says vaping products that contain nicotine are subject to "stringent controls" under the Tobacco and Vaping Products Act and the Canada Consumer Product Safety Act , which also contain marketing restrictions.

While the federal health agency says vaping "produces an aerosol that may contain dozens of chemicals," it only lists four ingredients when describing the contents of vaping vapour.

Companies are not required to put ingredient labels on vaping products in Canada.

"We don't have any regulations on what chemicals are allowed to be used in electronic cigarettes or what chemicals could be banned," Goniewicz said.

"[The industry is] changing so fast … figuring out what might be added to those products today that was not in the products that we tested five years ago, or even two years ago — that is a true challenge for scientists."

It's estimated there are more than 7,000 different flavouring chemicals in vaping liquids. While many are proven safe to eat, most of them have never been tested to evaluate their effect on lungs.

Goniewicz said the biggest question facing the vaping industry and health officials today is the long-term health consequences of e-cigarettes and liquids.

"People use the products on a daily basis. Kids puff on the device many times a day. They inhale high doses of nicotine. They inhale all those flavourings and additives," he said.

"We don't know what will happen with their lungs, their hearts, with their brains 10 years from now, 20 years from now."

Read more stories in this series:

Vaping regulations in Canada

Health Canada says it has seized more than 60,000 non-compliant products from vape shops and convenience stores across the country between July and October of this year.

Inspectors visited more than 1,000 locations across the country during that period, and more than three-quarters of the vape shops were found to be selling and promoting products that violate federal law, a Health Canada spokesperson said in a statement.

The most common violations were promoting child-friendly flavours and using testimonials to promote products.

Darryl Tempest of the industry group Canadian Vaping Association is calling for more marketing restrictions because of the uptick in vaping among young people. (Craig Chivers/CBC)

Darryl Tempest, executive director of the Canadian Vaping Association, which represents more than 300 Canadian retail and online vaping businesses, said vaping is safer in regards to the "comparative risk" to cigarettes.

"Vaping is far less harmful," he said. "It's not benign, no one suggested it is. What it is, is a lot less harmful for the 7,000 chemicals that you ingest or that you inhale as you smoke."

Tempest is calling for more marketing restrictions because of the uptick of youth use and said his organization welcomes more regulations from Health Canada.

Morisette said the current regulatory system in place in Canada is "backwards."

"People got access to all of those e-liquids without any clue of what they could do to their lungs," he said. "Now, we have hundreds of thousands of vapers in Canada inhaling things, [and] we don't know what they can do to their lungs and the rest of their bodies."

There are fewer restrictions on vaping devices in Canada than on tobacco, cannabis or even alcohol. Health Canada made e-cigarettes widely accessible based on an understanding that they could be used as a smoking cessation tool. Now, Canada is investigating almost a dozen possible or confirmed cases of vaping-related lung disease and the U.S. is tallying up thousands of lung injuries and over 40 deaths. 19:46

Vaping as a smoking cessation tool

Nicotine is a highly addictive substance, and there is little guidance available to people who want to quit vaping, unlike with smoking .

Health Canada's advice to people about vaping remains the same: If you don't vape, don't start. But the federal health agency also says that replacing cigarette smoking with vaping "will reduce your exposure to harmful chemicals."

"Vaping is less harmful than smoking," Health Canada says on its website . "Switching from tobacco cigarettes to vaping will reduce your exposure to many toxic and cancer-causing chemicals."

Goniewicz said he's heard anecdotally from people who call the smoking cessation phone lines at the Roswell Park cancer centre in Buffalo asking for help to quit vaping.

"Right now, we don't have any approved treatment on how to help them," he said. "I don't really know what to tell them."