Pod-mod vs. conventional e-cigarettes: nicotine chemistry, pH, and health effects

The rapid increase in popularity of pod-mods such as JUUL e-cigarettes, particularly in youth, has sparked many discussions on the possible harmful effects of JUUL. We spotlight key differences between JUUL, which contains 5% nicotine in benzoic salt form, and a conventional e-cigarette, Blu, which is claimed to contain 2.4% nicotine free base. We compared the measured pHs of JUUL and Blu E-liquids with pH values calculated based on chemical principles. The concentrations of protonated and unprotonated nicotine in these two kinds of e-cigarettes were also calculated. Theoretically, there is a clear distinction between the pH effects of the direct contacts of e-cigarette aerosol on the tissue in the inner surface of the respiratory tract and on other body systems via circulation after absorption. The concentration of protonated nicotine [the ligand of nicotinic acetylcholine receptors (nAChRs)] in JUUL (pH 6.0) is 7 times higher than in Blu that, hypothetically, excessively stimulates nAChRs that impact the epithelium inflammatory responses in the lungs and contribute to onset, progression, and proliferation of lung cancer. The concentration of unprotonated nicotine that readily diffuses across membranes (high absorption rate) in Blu (pH 8.26) is 26 times higher than that in JUUL. Based on pH and protonated versus unprotonated nicotine considerations, JUUL e-cigarettes potentially would lead to more detrimental effects on the lung, while conventional e-cigarettes such as Blu would lead to more systemic effects, such as on cardiovascular and nervous systems. Regulatory policies on the pH of E-liquid are implicated.