Several brands of electronic cigarettes, e-liquids, and other vaping products give off high levels of two cancer-causing chemicals even during normal use, according to tests commissioned by the Center for Environmental Health (CEH).

“More than half of the products we tested had levels above the California safety standard,” Charles Margulis, media director for CEH, told Healthline, and “many of the products were quite high.”

The tests prompted the nonprofit to file lawsuits against tobacco and other e-cigarette companies for failing to warn consumers about these chemicals, as required by Proposition 65, California’s consumer protection law.

CEH’s announcement comes on the same day as the American Cancer Society’s Great American Smokeout, an event designed to help people give up tobacco.

E-cigarettes, which usually contain nicotine, have been promoted by some companies as a tool for quitting smoking. Several studies, though, have found that e-cigarettes were not especially effective as a smoking cessation tool.

Read More: Are E-Cigarettes a Healthy Way to Quit Smoking? »

Toxic Chemicals Studied

Between February and July, CEH purchased 97 products from local and online retailers. These included disposable e-cigarettes, pre-filled cartridge devices, and devices that could be refilled with e-liquids.

CEH officials said tests by an independent laboratory revealed that the vapor produced by some of these devices contained formaldehyde at levels up to 473 times the California safety standard. Acetaldehyde levels were up to 254 times the safety standard.

Even the vapor produced by some of the nicotine-free e-liquids — sometimes marketed as safer — contained high levels of the toxins.

CEH officials noted that tests were done with devices set at temperatures typical of how people would use these vaping products. Earlier tests had been criticized for using unreasonably high temperatures.

Both formaldehyde and acetaldehyde are listed by the Environmental Protection Agency as probable cancer-causing agents.

E-cigarettes and other vaping products use a heating device to turn a liquid into a vapor that can be inhaled. The liquid varies among products, but generally contains propylene glycol or glycerol, flavoring compounds, and sometimes nicotine.

Even if the compounds in the e-liquid are not toxic, the intense heating need to create the vapor may produce potentially harmful chemicals.

Read More: Does Switching to E-Cigarettes Make Your Body Any Healthier? »

Lawsuit Targets Companies

CEH’s lawsuit targets tobacco companies, such as RJ Reynolds and Imperial Tobacco, and other e-cigarette companies whose products were found to contain cancer-causing chemicals in their vapor.

“We’d like to see this industry cleaned up,” said Margulis. “Ideally, they should produce products that either eliminate or significantly reduce the exposure to users of the cancer-causing chemicals.”

In response to an email query from Healthline, RJ Reynolds officials said they had no comment.

Makers of e-cigarettes and e-liquids may not be willing — or able — to change their products. But Proposition 65 requires them to provide a “clear and reasonable” warning to consumers about these chemicals.

“Obviously, e-cigarettes are a nicotine delivery device, so we don’t expect to eliminate nicotine,” said Margulis, “but they need to have the proper warning labeling about nicotine and, if they can’t reduce them, about the cancer-causing chemicals.”

Nicotine, formaldehyde, and acetaldehyde are all included on the Proposition 65 list of potentially harmful chemicals.

CEH’s legal approach may have support from consumers.

A recent survey by researchers at the University of Michigan found that more than 90 percent of teens and parents thought that e-cigarettes should carry health warnings similar to those used for tobacco cigarettes.

CEH officials also want e-cigarette companies to change their marketing practices. They want childproof packaging to protect children from accidental poisonings from e-cigarette liquid.

Read More: E-Cigarette Flavorings Can Be Toxic to Lung Cells »

Legal Approach May Have Limited Reach

A lawsuit filed by CEH earlier this year — about the reproductive health threats of nicotine — has already resulted in some changes in the e-cigarette industry.

One e-cigarette company has agreed to take steps to protect children, such as not marketing to children on television or teen websites, and not using teen models or cartoon characters in their advertising.

A separate lawsuit, filed last week by three people across the country, alleges that a California e-liquid manufacturer misled consumers by claiming its products were free of two other chemicals — diacetyl and acetyl propionyl.

While these lawsuits may bring more transparency to an industry with little regulation, CEH is realistic about what they will achieve.

“Even tobacco cigarettes, which are known to cause cancer, are still widely sold around the world,” said Margulis. “We’re not expecting to get [e-cigarettes] off the shelves. We do expect [companies] to abide by the warning requirements of the law.”