Atmospheric scientists at the Desert Research Institute (DRI) have turned their attention toward the growing e-cigarette industry and found that toxic aldehydes, such as formaldehyde, are formed during the chemical breakdown of the flavored e-liquid during the rapid heating process (pyrolysis) that occurs inside e-cigarettes or electronic nicotine delivery systems (ENDS).

Since the dose makes the poison, is this a concern? Not really, but in the modern world of International Agency for Research on Cancer (IARC) hazard assessments, risk has become irrelevant and the presence of any compound, even in trace levels, is declared carcinogenic if the levels are within seven orders of magnitude, so 10,000,000 to 1.

E-cigarette liquids have been marketed in nearly 8,000 different flavors, according to a 2014 report from the World Health Organization. U.S. Food and Drug Administration (FDA) surveys found that 16-percent of high school and 5.3-percent of middle school students tried e-cigarettes once in 2015, slightly more than cigarettes, making e-cigarettes the most commonly used tobacco-derived product among youth for the second consecutive year. In 2014, 12.6-percent of U.S. adults had ever tried an e-cigarette, and about 3.7-percent of adults used e-cigarettes daily or some days.

The authors measured concentrations of 12 aldehydes in aerosols produced by three common e-cigarette devices. To determine whether the flavoring additives affected aldehyde production during vaping, five flavored e-liquids were tested in each device. In addition, two unflavored e-liquids were also tested. The devices used in the study represented three of the most common types of e-cigarettes - bottom and top coil clearomizers, and a cartomizer.

The study avoided any variation in puff topography (e.g., puff volume, puff velocity, interval between puffs) by utilizing a controlled sampling system that simulated the most common vaping conditions. E-cigarette vapor was produced from each device by a four-second, 40-ml controlled puff, with 30-second resting periods between puffs. The e-cigarette devices were manually operated to replicate real-life conditions and all samples were collected in triplicate to verify and confirm results. Specific care was taken to avoid "dry puff" conditions.

To prove that the flavoring compounds, not the carrier e-liquid solvents (most commonly propylene glycol and/or vegetable glycerin) dominated production of aldehydes during vaping, the authors performed a series of experiments in which a test flavored e-liquid was diluted with different amounts of the unflavored e-liquid. Liquids with higher flavor content produced larger amounts of aldehydes due to pyrolysis of the flavoring compounds.

In all experiments, the amount of aldehydes produced by the flavored e-cigarette liquids exceeded the American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs) for hazardous chemical exposure.