As e-cigarette use skyrockets, so too do studies of their chemistry. The handheld devices generate vapors from nicotine-containing liquids, and most work has focused on the stages of that transformation. Fewer studies have examined the chemistry occurring inside e-cigarette users’ mouths, but Silvia Balbo surmised her team’s mass spectrometry technique could provide insight. The technique analyzes reactive carbonyl compounds appearing in mouths after alcohol exposure, and the glycerol or propylene glycol in e-cigarette liquids generate similar compounds. Balbo and postdoctoral researcher Romel Dator, who presented the work at last week’s ACS national meeting in Boston, recruited five users and collected saliva before and after 15-minute vaping sessions at their University of Minnesota Masonic Cancer Center clinic. After vaping, levels of acrolein and methylglyoxal in users’ saliva increased by as much as 50 times. To examine potential damage by these compounds to DNA, users swished a saline mouthwash to provide oral cells. Compared to nonvaping controls, four of the five users had increased levels of γ-hydroxy-1,N2-propanodeoxyguanosine, an acrolein-DNA adduct. The team next plans to compare e-cigarette users with traditional cigarette smokers. Balbo cautioned that her small study was designed to analyze chemical exposures, not to demonstrate that e-cigarettes cause cancer.