More than half of Europeans now think that e-cigarettes are harmful--a proportion that has nearly doubled in two years--show the latest results of a European Union (EU)-wide survey, published online in the journal Tobacco Control.
Yet use of these devices across member states has continued to surge within the same timeframe, the findings show.
The researchers analysed responses to two Eurobarometer for Tobacco surveys carried out in early 2012 and late 2014, on the perceptions and use of e-cigarettes, among a representative sample of adults (15+ years) from 27 EU member states, excluding Croatia.
In all, just under 27,000 people in both years answered questions on frequency of use; reasons for use; perception of harms; current tobacco use; and provided information on age, sex, educational attainment, and household financial security.
The proportion of people who said they had ever tried an e-cigarette rose from 7.2% in 2012 to 11.6% in 2014 across member states, although this figure varied widely by country, ranging from 5.7% of respondents in Portugal to 21.3% in France, for example.
And in Malta, survey respondents were more than five times as likely to say they had tried an e-cigarette in 2014 as they were in 2012.
Furthermore, in 2014, around one in seven people who said they had ever tried an e-cigarette defined themselves as a current user of these devices, indicating that they had shifted from experimentation to use, say the researchers. But once again, this varied by country, ranging from 1.7% in Slovenia to 28.9% in Portugal.
Current smokers were 23 times more likely to say that they had ever tried an e-cigarette while ex-smokers were more than 6.5 times as likely to have done so.
Being in the age range 18-24, living in a town/city, and being more highly educated were also linked to increased odds of ever having tried an e-cigarette.
Those who defined themselves as current vapers were more likely to be older. And they were nearly three times as likely to say they had started vaping because they thought e-cigarettes could help them quit smoking, and more than twice as likely to say they had done so to get round smoking bans.
The attractiveness of e-cigarettes had no bearing on the decision to become a regular vaper, the responses showed.
But despite the rising overall popularity of e-cigarettes, the proportion of those who felt these devices posed a health risk nearly doubled between 2012 and 2014.
In 2012, around one in four people (just over 27%) believed them to pose a health risk. By 2014 this figure had risen to more than 51.5%.
Yet again, this figure varied widely, from just over 31% of respondents in Hungary to just over 78% in The Netherlands. The UK had one of the lowest proportions of citizens who thought e-cigarettes were harmful.
Nevertheless, almost a third of all respondents (29%) said they didn't know whether e-cigarettes were harmful, which indicates prevailing levels of uncertainty about their safety, suggest the researchers.
They point out that as their study was cross-sectional, meaning that data were collected from each participant at a single point in time, caution should be applied to any assumptions about causal relationships.
Variations in responses may be partly explained by the differing rates of smoking across EU member states as current and former smokers were much more likely to have tried e-cigarettes, they say.
Other factors, such as the way in which e-cigarettes are advertised and/or promoted as a smoking cessation aid, and their affordability, are also likely to have a role, they add.
"A better understanding of the population-level use and impact of e-cigarettes within the EU is needed, especially of the potential impact on smoke-free laws, smoking initiation and cessation," they conclude.