As regulatory clouds continue to gather over the electronic cigarette industry, public health researchers have set their sights on the potential risks these products pose to non-users. A study published this month in conjunction with the FDA’s second public workshop on e-cigarettes claimed that bystanders may be exposed to aerosol particles smaller than 1,000 nanometers, similar in size to tobacco smoke and diesel engine exhaust. The aerosol, according to the study’s authors, contains nicotine, glycerin/glycols, artificial flavorings, and preservatives.

“As proliferation of e-cigarettes surges, understanding the health effects of e-cigarette use and exposure to vapors is essential,” said study author Jonathan Thornburg of the nonprofit research group RTI International. “We need to be aggressively investing in and conducting research that answers lingering questions about the potential health impacts of secondhand exposure to e-cigarettes, while taking the necessary action to protect public health now.”

Despite the alarm evident in its tone, the RTI study does not purport to find that secondhand exposure to e-cigarette vapor actually causes harm.

The study measured the concentration and diameter of aerosol particles, not the way they affect the health of nonusers. The researchers acknowledge that the size and distribution of particles depends on the chemical composition of the of the e-liquid, the device operation, and user vaping preferences. Design characteristics vary between e-cigarettes, and scientists lack new standards for testing emissions and secondhand exposures across multiple device types. Moreover, a 2014 Drexel University study found that even the vapers themselves were not exposed to levels of hazardous substances in excess of recognized workplace exposure standards (known as Threshold Limit Values). One may expect secondhand exposures to be substantially lower than those of actual users; the RTI study estimated, for instance, that vapers exhale 50% of the e-cigarette emissions they inhale.

Research into the potential risks (if any) of e-cigarette use is in its nascent stages. Even less is known about the effects of secondhand e-vapor exposure. Yet this research — and the way that its findings are interpreted by the media and regulators — may have the greatest potential to shape the products vapers turn to in their search for a safer alternative to smoking, and circumscribe the places where they may use such products.