A Review on Different Animal and Human Studies to Evaluate the Safety of Inhalation of Propylene Glycol in E-Cigarettes

This chapter aims to evaluate the safety of inhalation of propylene glycol in e-cigarettes. In recent years, e-cigarettes have become increasingly popular. Electronic cigarettes, or "e-cigarettes," are a safe substitute for tobacco use in tobacco products or as a tool for cessation smoking. However, the FDA believes that e-cigarettes are just as dangerous as traditional cigarettes. Instead, the American Association of Public Health Physicians' Tobacco Control Task Force has stated that e-cigarettes closely resemble Nicotine Replacement Therapy devices. All animal and human research that investigated the effect of PG inhalation concluded that PG did not appear to constitute a major risk via the inhalation route. In fact, in several of these animal trials, the PG doses employed were higher than in e-cigarettes and had no deleterious consequences. However, no human investigations have been conducted at the level of e-cigarette concentrations. This review sheds some light on the safety implications of PG inhalation, particularly as it relates to e-cigarette concentration, as demonstrated in animal research. Since the majority of the findings originated from animal studies, the data can be utilized to launch human studies to assess the short and long-term health impacts of propylene glycol in e-cigarettes. The human physiology is different as compared to the animal physiology. Therefore, further human studies using PG concentrations similar to that in e-cigarettes need to be conducted to confirm the short term and long-term safety of inhalation of PG from e-cigarettes.