Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways.

Introduction:
This article investigates the impact of heating conditions in electronic cigarette (e-cigarette) devices on the properties of the generated aerosols. The study aims to assess the spatial and temporal temperature distribution of an e-cigarette device, the mass and nicotine content of the aerosols, the viscosity and ph of the aerosols, the color of the aerosols, and the metal contents in the aerosols. The findings demonstrate that heating conditions in e-cigarettes change the physicochemical properties of the aerosols and their metal contents, thereby possibly affecting users' oral and respiratory systems.

Key Points:

* The study assessed the spatial and temporal temperature distribution of an e-cigarette device using an infrared (IR) camera and thermocouples.
* The mass and nicotine content of the aerosols, the viscosity and ph of the aerosols, the color of the aerosols, and the metal contents in the aerosols were measured.
* The maximum e-liquid temperature measured by the IR camera increased from 198.9 to 280.8°C as the power increased from 20 to 80 W.
* The averaged mass of the aerosol proportionally increased with the power, and the nicotine mass contained in the aerosols at 20 W was only 7.86 mg/puff, which was significantly lower than that at the other power levels.
* The viscosity of the aerosols gradually increased as the amount of vaporization of VG increased at higher operation powers.
* The ph of the aerosol did not change in various operation power settings, and the average ph values of the captured aerosols were uniformly measured in the range of ph 8.4-8.8.
* The collected aerosol solution generated at 20 W looked visually similar to the e-liquid, while the aerosol solution generated at 80 W was noticeably more yellow.
* The metal contents in the aerosols gradually increased as the operation power increased, and the sources of as, Cd, Pb, and Mg, which were not detected in the EDS analysis of the heating coil and the coil head, were still unknown.

Main Message:
The study highlights the importance of regulating the heating conditions in e-cigarette devices to ensure the safety of users. The findings demonstrate that high power settings result in higher temperatures, which can lead to the aerosolization of a viscous component in the e-liquid, increasing the viscosity of the aerosol. additionally, high power can lead to nicotine prone to oxidation, resulting in the color of the aerosol turning yellow. The study also showed that e-cigarette aerosol could contain various metals, including aluminum, arsenic, cadmium, chromium, copper, iron, magnesium, nickel, lead, and zinc. although these metal contents proportionally increased with the power setting, they remained far below the recommended exposure limits. Therefore, it is crucial to regulate the heating conditions in e-cigarette devices to minimize the potential health risks associated with the inhalation of harmful chemicals and metals.

Komura M, Sato T, Yoshikawa h, et al. Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways. Respiratory research. 2022;23(1):216. doi:10.1186/s12931-022-02142-2