Data on the daily exposure from cigarettes (the average [±SD] of all values [milligrams of formaldehyde per cigarette]) were derived from Miyake and Shibamoto2 and Counts et al.3 These values were multiplied by 20 cigarettes per pack. Thus, they are an average of the values used in the protocols from the International Organization for Standardization, the Massachusetts Department of Public Health, and Health Canada. Data on the daily exposure from e-cigarettes from the formaldehyde gas phase were calculated from the data in Kosmider et al.4 We estimated daily exposure by applying our measured e-liquid consumption rates of 0.13 mg per milliliter (at 3.3 V) and 0.18 mg per milliliter (at 5 V) of vapor produced to the measured gas-phase formaldehyde values described by Kosmider et al.4: 0.13 μg per 1050 ml of vapor (at 3.2 V) and 27 μg per 1050 ml vapor at (4.8 V) for mixed glycerol and propylene glycol samples. Data on the daily exposure from liquid-phase aerosol particulate matter in e-cigarettes were calculated as the value of formaldehyde (as a formaldehyde-releasing agent [FRA]) exposure per day for commercial e-liquid (Halo “café mocha” flavor, 6 mg per milliliter of nicotine), measured from 10 successive aerosolized samples analyzed at 3 concentrations each. FRAs were identified by means of nuclear magnetic resonance spectroscopy (see the Supplementary Appen