E-cigarettes (electronic nicotine delivery systems) contain a battery that heats up liquid in a cartridge, tank or pod to produce a breathable aerosol that you inhale. They are also known as vapes, vaporizers, e-hookah sticks, e-hookahs and personal vaporizers (PVs). They are used to mimic conventional cigarettes and often contain nicotine and flavorings but do not burn tobacco or paper. Many people use e-cigarettes to help them quit smoking or to reduce their smoking habit but research is scarce on their long-term effects on human health.

E-liquids contain a mixture of solvents and flavourings. The most common are propylene glycol (1,2-propanediol) and glycerine (1,2,3-triol), which are food grade additives that are considered safe by the FDA. Other compounds include volatile carbonyls emitted during the heating of the liquid, which contribute to the sensorial properties of the vapors generated. Some e-liquids may even contain tetrahydrocannabinol, which can be used to deliver cannabis or other psychoactive drugs.

The concentration of nicotine in e-liquids ranges between 0 (zero, nicotine-free option) and up to 20 mg/mL (2%), which is the maximum permitted by European Union regulations. However, nicotine content labelling in the e-cigarette industry is not always accurate and incidences of mislabelling have been reported [1, 2].

The toxicological effects of e-cigs are currently under investigation. Several studies indicate that short-term e-cig consumption can cause harmful effects on the cardiovascular system such as platelet activation and endothelial dysfunction, but the impact of chronic e-cig use remains unclear. Similarly, data on the effects of e-cigarettes on the respiratory tract are scarce and conflicting.

Recently, a commonly commercialized creme brulee-flavoured e-cigarette aerosol was found to contain high concentrations of benzoic acid, which is an established respiratory irritant in human lung epithelial cells. A similar study using an unflavored aerosol from a popular disposable e-cigarette indicated that it could induce airway inflammation, possibly due to the inhalation of volatile carbonyls containing benzoic acid.

Another concern is that e-cigarettes may contribute to the development of chronic obstructive pulmonary disease (COPD) in current smokers. Although a number of COPD patients have successfully switched from smoking to e-cigarettes, there is a risk that their use may increase the rate of exacerbations and therefore reduce the quality of life of these patients. This should be a major consideration in the decision to prescribe or recommend e-cigarettes to smokers with COPD. The potential for COPD to be aggravated by switching from smoking to e-cigarettes is a serious issue that requires urgent research. The results of such investigations will have a direct impact on public health policy and regulation. Furthermore, they will help to inform future clinical trials that are needed to determine whether e-cigarettes can be recommended as an effective smoking cessation aid for smokers with COPD. To do so, a clear understanding of the underlying mechanism is required, including the role of e-cigarettes in the cellular and molecular mechanisms that promote or prevent the onset of COPD. This knowledge is necessary for the development of novel and more effective strategies to promote cessation from smoking. 電子煙