Nicotine salt acid choice influences phenol emissions in a sub-ohm e-cigarette: salicylate versus benzoate

Background Sub-ohm electronic cigarettes (ECIG) operate at higher power levels than their counterparts, leading to greater thermal degradation of e-liquid components and the formation of toxic compounds. Although phenolic compounds have been detected in ECIG aerosols, the effects of nicotine salt formulations are not well understood. Methods This study examined how different e-liquid components (nicotine, nicotine salt type, propylene glycol (PG)/vegetable glycerin (VG) ratio) influence phenolic compound formation using two power settings (45 W and 60 W) of a sub-ohm device. E-liquids with nicotine benzoate and salicylate were prepared with various PG/VG ratios (0/100, 30/70, 50/50, 70/30, 100/0), and aerosol samples were analysed via Gas Chromatography-Mass Spectrometry (GC-MS). Results Aerosol mainly contained unsubstituted phenol, with other phenolic compounds below detection limits. Additionally, nicotine benzoate formulations produced low phenol fluxes (2.1–4.5 ng/s), whereas nicotine salicylate emitted much higher levels (99–574 ng/s). With phenol levels falling within the range reported for IQOS and waterpipe products, while remaining at the lower end of the range observed for combustible cigarettes. Toxicological analysis showed that ECIG users heavily smoking nicotine salicylate e-liquids are exposed to phenol levels close to the Acute Exposure Level Guidelines (EPA AEGL1). Conclusions The results highlight a regulatory concern where nicotine salt choice can significantly alter the toxicant profile. Therefore, nicotine salt formulation should be considered a key factor in ECIG safety, and regulators may need to limit harmful acid additives to protect public health. Moreover, a standard puffing method for direct-to-lung devices should be established to ensure consistency in future research.