Table 1.

Some factors reportedly related to e-cigarette use:

Regulation: International variability [102]; increasing number of countries banning e-cigarettes [103]. Strong regulation can protect CYP from e-cigarettes	South Korea: since 2008, regulates e-cigarettes as tobacco products with prohibitions on indoor use, sales to minors, advertising bans, health warnings and taxes	Prevalence of the use in CYP remained stable at about 4% between 2011 and 2015
	USA: Until recently there has been little federal regulation and some restriction on the sale of e-cigarettes to CYP.	Rose dramatically from 1% to 11% during the same period [104]. High school student use has risen from 13% in 2014 to 27.5% in 2019 [105]. Approximately 2.1 million middle and high school students had used e-cigarettes in the past 30 days [106]
	UK: prior to 2015 e-cigarettes were only regulated as consumer products. Since October 2015 the sale of e-cigarettes containing nicotine to under 18 s was made illegal. On 20th May 2016, any advertising or promotion of electronic cigarettes and re-fill containers on any media platforms was prohibited. The only advertising still allowed is at point of sale and other location specific advertising such as billboards, and advertisements must meet regulations designed to prevent promotion to people under 18	The number of current e-cigarette users continues to grow as rise [35] (Table 2)
Experimentation: seems to be a major reason for the increased use of e-cigarettes by CYP	International Tobacco Control Four-Country Survey (USA, Canada, the UK and Australia), found that the prevalence of trying e-cigarettes was higher in young, nondaily smokers because of the perception that they were are not harmful or are less harmful compared with CSTPs. Health warning labels on nicotine vaping products (mandatory in England, not in USA, Canada, Australia) may not be noticed [107]	Cited reasons for use [35]: –‘Just to give it a try’: •52.4% of the users (current, ex-users and those who had tried at least once) •70.6% amongst never smokers –‘I like the flavours’: 14.4% –‘other people use them so I join in’: 12.7% –‘I think they look cool’: 1%
Acquisition: CYP can easily acquire vaping products	Minors are easily able to purchase e-cigarettes (and indeed CSTPs [108])) from the Internet because of an absence of age-verification measures [109]. Tobacco retailers are less likely to ask for identification, and more likely to sell to minors attempting to buy vaping products as compared to CSTPs [110]	61.9% buy them (most common means of purchase the internet: 24.5%) 35.2% are given them (most common source is friends: 24.5%) [35] In the recent EVALI outbreak (50% of those who reported using THC-containing products provided data on product source; 16% were only from commercial sources (recreational and/or medical dispensaries, vape or smoke shops, stores, and pop-up shops); 78% only from informal sources (family/friends, dealers, online, or other sources); 6% reported acquiring products from both sources [111]
CSTP initiation and use: E-cigarette use particularly among low-risk CYP is associated with increased risk for CSTP initiation and use [112]	Longitudinal studies [33], [113], [114], [115], [116], [117], [118] in the US and Canada [119] have shown a correlation between e-cigarette exposure and initiation and continued use of CSTP among CYP.	Two separate meta-analyses (91051 and 17389 CYP) [120], [121] estimated that never-smoking adolescents and young adults who used e-cigarettes had between 2 and 4.3 times increased odds of intention to progression to cigarette smoking compared to never users. E-cigarettes appear to encourage CYP progression to established smoking [122]; and even if they do not nicotine-addiction must be prevented. E-cigarette devices may be a delivery system for illicit drugs [123]
Dual use: More than 60% of smokers wish to quit because they do not like being dependent [124], but switching to e-cigarettes does not break the nicotine addiction and indeed dual use is more risky than CSTP use	South Korea: e-cigarette use was strongly associated with current and heavier cigarette smoking [125] so those who had tried to quit CSTPs were more likely to use e-cigarettes but less likely to no longer use CSTPs
	UK:	In 2019, 39.8% of CYP were dual users [35]