Inhaling vapor from E-cigarettes is as safe as breathing air, according to a new paper that compared two E-cigarettes with regular cigarettes and air.

Research published in Toxicology in Vitro used a combination of tests to find out whether E-cigarette vapor is harmful to people’s airways. To model the possible harmful effect of E-cigarette vapor, which contains among other things nicotine and flavorings, British American Tobacco partnered with tissue engineering firm MatTek to use a smoking robot with respiratory tissue.

After six hours of exposure to tobacco smoke, cells died off but after an “aggressive and continuous” dose of vapor, the effect on airway tissue was “similar to that of air.”

“By employing a combination of a smoking robot and a lab-based test using respiratory tissue, it was possible to demonstrate the ability to induce and measure aerosol irritancy and to show that the different e-cigarette aerosols used in this study have no cytotoxic effect on human airway tissue,” said BAT spokesperson Dr Marina Murphy.

BAT claim the new methodology could be used to help develop product standards and testing for E-cigarettes in the future. “Currently there are no standards concerning the in vitro testing of e-cigarette aerosols,” said Marina Trani, Head of R&D for British American Tobacco’s next generation nicotine products. “Our protocol could prove very useful in helping the process by which these guidelines might progress,” she added.

The study comes as state lawmakers in California proposed to ban the use of E-cigarettes in public places. Democratic Sen. Mark Leno of California is sponsoring the bill as part of a series of anti-tobacco crackdowns.

“Decades ago, the tobacco industry tried to fool us into believing that filtered cigarettes were a healthier alternative to traditional cigarettes, and now they’re making the same claims about e-cigarettes,” said Leno. He went on to claim that the tobacco industry is “using a new delivery system, which is currently addicting the children of California to toxic nicotine.”

While the authors of the study confirm the consensus view that E-cigarettes are far less harmful than regular tobacco products they say that “further studies are required to fully assess their safety for long-term use”

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