Our study found that e-cigarette-only users report more perceived improvement in health and less adverse health effects of vaping than dual users. The majority of e-cigarette-only users reported better respiratory and sensory functions and indicated only minor AEs since they started using e-cigarettes. However, dual users were probably under-represented while satisfied e-cigarette-only users were over-represented, therefore, our results may overestimate perceived benefits of vaping [14, 23]. Furthermore, the majority of respondents were heavy smoker before e-cigarette use initiation, and only about 10% were light smoker. To our knowledge, this is the first study to explore different dimensions of perceived health changes due to e-cigarette use in a mostly past heavy smoker sample.
Improved olfactory and gustatory functions, both sensory improvements, were frequently reported benefits of vaping in both independent and sponsored studies [13, 15, 17, 23]. High intensity past tobacco smoking and longer e-cigarette use history predicted greater sensory improvements, but only among males. Olfactory dysfunction is more likely among current smokers compared to never smokers, and reduced olfactory ability depends on tobacco smoke dose-duration . Furthermore, smoking-related olfactory dysfunction is reversible due to reversible squamous metaplasia of the olfactory mucosa . Gustatory dysfunction may rather reflect olfactory dysfunction , which can explain combined improvement of taste and smell sensation after smoking cessation. Lower exposure to potentially toxic substances from e-cigarettes compared to combustible cigarettes  might have a similar but likely weaker effect on the olfactory mucosa similar to cessation, which leads to the regeneration of squamous metaplasia within six months .
Improved breathing, general physical status and stamina were correlated with past combustible cigarette smoking habits and e-cigarette use duration. The most commonly reported improvement among these physiological functions was breathing in our whole sample, consistent with studies of Dutch vapers, and a large international sample of a sponsored study involving more than 19,000 e-cigarette users where almost 90% of respondents reported better breathing due to vaping [13, 17, 23]. However, studies investigating respiratory outcomes of e-cigarette use are contradictory. Some studies have demonstrated that short-term e-cigarette use has an acute negative effect on the respiratory system, like impaired lung function and increased airway resistance both among healthy smokers and nonsmokers, and smokers with asthma or COPD [20, 26]. In contrast, others reported no significant short-term changes in lung function parameters among healthy smokers switching to e-cigarettes [18, 27], although studies sponsored by e-cigarette manufacturers and merchants found improvements in spirometric indices and respiratory symptoms on long-term [28, 29]. A large proportion of Hungarian e-cigarette-only users indicated improvement in physical status and endurance similarly to other studies [13,14,15, 17, 23]. These positive changes may be associated with perceived improvements in respiratory health.
E-cigarette-only users experienced significantly greater improvements in mental health. They reported greater improvements in their mood and quality of sleep compared to a large international study  and a smaller one from the Netherlands . However, a study by Adriaens et al. (2017) did not detect significant differences between dual users and switchers (smokers who completely switched to e-cigarette use) in moderate improvement of mood and sleep quality . Possible explanations for mood improvement could be positive expectancies towards e-cigarette use , satisfying control on nicotine delivery by advanced generation e-cigarettes , perceived supervision of withdrawal symptoms , and self-efficacy to change tobacco smoker identity toward a perceived healthier e-cigarette user identity. Adult smokers and former smokers with mental health conditions seem to be more susceptible to trying e-cigarettes and to be current vapers as they perceive them an appealing and less harmful substitutes for conventional cigarettes . Improvements in mood and psychological quality of life as well as perceived better respiratory function might explain positive changes in sleep quality. Nevertheless, a study examining online e-cigarette forum posts related to positive and negative health effects of e-cigarette use explored more negative complaints than positive changes of sleep disorders .
Positive changes in memory were reported by a minority of our sample similarly to another study . A previous research explored that memory improved only among individuals using nicotinic e-cigarettes presumably because of impaired memory during smoking abstinence that was reversed by nicotinic e-cigarettes .
Sexual performance has rarely been investigated as it pertains to e-cigarette use. Approximately one third of e-cigarette-only users in our sample agreed that their sexual performance improved since they initiated vaping, similarly to an international study which found 28.9% improvement rate . This association is suspected to be complex. On the one hand, nicotine may cause acute vasospasm while other components of tobacco smoke are atherogenic on a dose-response manner both in the male and female genital tract [33, 34]. If e-cigarettes deliver much less toxicants than conventional cigarettes , but nicotine delivery by advanced generation devices are as effective as by conventional cigarettes , improvement in sexual performance might be expected in individuals with shorter duration and less intense lifetime smoking. On the other hand, better-functioning respiratory and sensory systems may positively influence sexual performance of former smokers switching to e-cigarettes.
Almost two-thirds of dual users and more than half of e-cigarette-only users did not report improved appetite consistent with a few other studies detecting greater improvement in appetite among switchers compared to dual users [17, 23]. It is suspected that both nicotinic and nicotine-free e-cigarettes may prevent weight gain through influencing body metabolism by nicotine and other e-liquid constituents, and providing an alternative activity to eating by replacing high calorie foods with sensory experiences like desirable taste and smell of the vapor [35, 36]. A recent study explored that the popular vanilla-flavored e-liquid was associated with vaping to lose/control weight as it may serve as a distractor from or substitute for high calorie foods . Carbohydrate intake increases after cessation because former smokers perceive the sweet taste more pleasant than smokers possibly due to the activation of central reward centers during nicotine withdrawal . E-cigarettes may have the potential to support and sustain quitting by reducing appetite and weight gain, but in contrast they may also promote the initiation of e-cigarette use for appetite/weight control purposes among non-tobacco users .
In our analysis, we also identified three main dimensions of perceived health improvements attributed to e-cigarette use. Sensory improvement included improved smell and taste. The improvement in physical functioning encompassed improved breathing, physical well-being and improved stamina. Finally, the mental health improvement factor incorporated the improved appetite, sexual life, mood, memory and sleeping. We also noted that dual users reported much lower degree of improvement in all three dimensions than e-cigarette-only users. This result highlights that greater perceived health improvements are related with the complete cessation of regular cigarette use. Longer duration of e-cigarette use was associated with higher score on sensory improvement and physical functioning. Interestingly, intensity of smoking before e-cigarette use was also associated with greater improvement in sensory and physical functioning dimensions suggesting that heavy smokers compared to light smokers may gain much more from switching to e-cigarette from combustible cigarette. Furthermore, our study provides a useful self-report tool to measure perceived health effects due to vaping for future studies.
Regarding AEs, mouth and throat, respiratory and neurological symptoms were the most frequently reported by a minority of Hungarian vapers parallel with other studies indicating similar side-effect patterns [16, 17, 19, 20, 23, 27]. Possible explanations of mouth and throat symptoms are multiple. Longer and harder puffing with stronger vacuum is necessary for vaping than for conventional cigarette smoking to produce aerosol . Vacuum generation might involve the tongue, the palate and also the bucca, therefore, these oral regions may be exposed more directly to the vapor . Moreover, glycerin, propylene-glycol, and e-liquid flavorings might form thermal degradation byproducts during vapor generation which may be also a cause of tongue and/or buccal pain as well as mouth and throat irritation [19, 39]. Finally, inhalation of e-cigarette aerosol elements like silicon, sulfur, calcium, titanium, and lithium are associated with throat irritation . Gingivitis and gum bleeding were experienced by our respondents like in previous studies [17, 40]. It is suspected that tobacco smoke-generated vascular changes in the gingiva resolves similarly during vaping and smoking cessation, that is, inflammatory response increases and vasoconstriction decreases in the gingiva .
Among AEs, cough was more frequently reported especially by dual users than breathing difficulties. However, cough was less commonly mentioned in our sample compared to previous studies reporting frequencies between 12.8–69.0% [17, 18, 20, 28]. Possible mechanism of cough is a vagal mediated protective reflex generated by inhaled irritants from the vapor like propylene-glycol and/or flavorings . Experiencing neurological AEs (e.g., headache and dizziness) were rare among Hungarian vapers, although some previous studies indicated more common occurrence [16,17,18, 27]. Cardiovascular AEs such as heart palpitation and chest pain were also infrequent especially among e-cigarette-only users compared to other studies [16, 17, 20]. A possible mechanism of neurological and cardiovascular symptoms is short-term increase of heart rate and blood pressure following e-cigarette use, however findings on blood pressure changes after vaping were inconsistent in previous studies . Additionally, learning period of puffing behavior with a newer generation e-cigarette could result in a nicotine boost and possibly excessive nicotine delivery may leads to increased heart rate and chest pain due to myocardial hypoxia [2, 41]. Other AEs were sporadic and even less frequent than reported in previous studies [16, 17].
This study provides more insights to patterns of perceived beneficial and adverse health effects of vaping, however, limitations exist. First, self-reported data are prone to recall and social desirability bias, particularly past tobacco smoking habits and experiencing AEs and physiological changes. Second, individuals with more positive perceptions and experiences of vaping may have been more motivated to participate in the survey leading to respondent bias. Third, the cross-sectional design and convenience sample limit causal inference. Fourth, we cannot separate the impact of positive expectancies for vaping or a placebo effect from improvements due to reducing combustible cigarette use or quitting smoking. Furthermore, we cannot exclude also the possibilities of a general response tendency toward the improvement in functions in self-report due to cognitive dissonance or other self-servicing biases. The possibility of these effects is reflected in relatively high correlations between factors of perceived health improvement. Sixth, like prior research, we did not compare perceived health impacts of switching to e-cigarettes to complete tobacco use abstinence which would be the optimal strategy to reduce tobacco-induced harm. We also do not have data on the long-term stability of the perceived benefits. Seventh, perceived improvement in health is influenced by several factors that we may did not measure which can explain the relatively low explained variance of health improvement factors. Further research should investigate those factors that can influence how e-cigarette users perceive and report health benefits from their product use. Finally, this study similar to others, is based on a convenience sample of users, therefore the generalization of results is limited, however having a representative sample of e-cigarette users is difficult to define, and rarely applied in e-cigarette research. Furthermore, the pattern of e-cigarette use is continuously changing which may also limit the generalizability of our results.