Sensory appeal and puffing intensity of e-cigarette use: Influence of nicotine salts versus free-base nicotine in e-liquids

Background: In the US, nicotine salts (with protonated nicotine instead of free-based nicotine) have been reported to lower the harshness and bitterness of e-cigarette aerosols, making it easier to inhale high levels of nicotine. This study aimed to determine whether nicotine salts also increase sensory appeal at lower concentrations (< 20 mg/mL). Moreover, and novel, inhalation intensity of both types of e-liquids was compared. Methods: In a randomized, double-blinded, within-participants design, healthy adults who use e-cigarettes (n=68) vaped tobacco-flavored e-liquids containing 12 mg/mL of free-based nicotine or nicotine salt ad libitum, using their own device, during two online sessions (June-July 2021, Utrecht, The Netherlands). The sensory parameters perceived liking, nicotine intensity, harshness, and pleasantness were rated on a 100-unit visual analog scale. The intensity of use was determined by the recorded puff number, duration and interval. Results: Test scores on appeal, harshness and puffing behavior parameters showed no significant differences between the nicotine salt and the free-base condition. The average inhalation time was 2.5 seconds. Additional analyses found no significant effect of liquid order, age, gender, smoking status, vaping frequency and familiarity with nicotine salts. Significant positive correlations were found between the sensory parameters except for harshness. Conclusions: Contrary to a previous study that used higher nicotine concentrations and standardized puffing conditions in a laboratory setting, we did not observe the effects of nicotine salts on sensory appeal in our real-life study paradigm. Moreover, we did not see effects on study parameters related to puffing intensity.