Center for Environmental Health says tests concluded majority of popular brands contained cancer-causing chemicals formaldehyde and acetaldehyde

A health watchdog is to take legal action in California against the manufacturers of some of the best-known brands of e-cigarettes, following tests to establish the levels of toxic chemicals they contain.

The Center for Environmental Health (CEH) says its tests found that nearly 90% of the companies had at least one brand that produced high levels of one or both of the cancer-causing chemicals formaldehyde and acetaldehyde.

In the first ever large lab-testing of e-cigarettes on the market, the CEH found that most – 50 of 97 products examined – contained high levels of one or both chemical.

The lab tests and legal action will fuel the battle raging over e-cigarettes. While supporters say they could help thousands of people give up the far more dangerous tobacco-filled conventional cigarettes, others worry about the chemicals they contain.

Such suspicions are fuelled by the involvement of major tobacco companies in the e-cigarette market. Critics say e-cigarettes may be a stalking horse for Big Tobacco, in order to rehabilitate the act of smoking.

The CEH said its lab tests of 97 e-cigarette and vaping products revealed levels of formaldehyde and acetaldehyde that violated California’s safety standards. It said this was the first time e-cigarettes had been tested by simulating their real-world use.

“For decades, the tobacco industry mounted a campaign of lies about cigarettes, and now these same companies claim that their e-cigarettes are harmless,” said Michael Green, executive director of CEH.

“Anyone who thinks that vaping is harmless needs to know that our testing unequivocally shows that it’s not safe to vape.

“This is especially troubling given the reckless marketing practices of the e-cigarette industry, which targets teens and young people, and deceives the public with unfounded health and safety claims. Our legal action aims to force the industry to comply with the law and create pressure to end their most abusive practices.”

CEH is invoking California’s consumer protection law, known as Proposition 65. Earlier this year, the watchdog started legal action against the companies for failing to warn users about the risks of nicotine in the products.

The non-profit organisation purchased e-cigarettes, e-liquids and other vaping products from major retailers including RiteAid and 7-Eleven, and from many online retailers and Bay Area vape shops between February and July 2015.

It commissioned an independent lab accredited by the American Association for Laboratory Accreditation to test 97 products, including 15 disposable “cigalikes” e-cigarettes, 32 cartridge devices and 50 refillable devices, for formaldehyde and acetaldehyde.

The two chemicals are known to cause cancer and are also linked to genetic damage, birth defects and reduced fertility. The lab used standard smoking machines that simulate how consumers use the products.

Almost 90% of the companies whose products were tested (21 of 24 companies) had one or more products that produced hazardous amounts of one or both of the chemicals, in violation of California law.

The testing showed that 21 products produced a level of one of the chemicals at more than 10 times the state safety standard, and seven products produced one of the chemicals at more than 100 times the safety level.

The CEH testing found high levels of the chemicals even in several nicotine-free varieties. For example, one nicotine-free product produced acetaldehyde at more than 13 times the state legal safety threshold and formaldehyde at more than 74 times the threshold.