Every adolescent tries something new, many try smoking. I would prefer they try e-cigarettes to regular cigarettes." Dr Le Houezec added.
Many are now calling for the industry to be regulated.
Konstantinos Farsalinos, from the University Hospital Gathuisberg, Belgium, said it was important for some light regulation to be put in place "as soon as possible".
"Companies are all hiding behind the lack of regulation and are not performing any tests on their products, this is a big problem."
Prof Farsalinos studies the health impacts of e-cigarette vapour. Despite the lack of regulation, he remained positive about the health risks associated with inhaling it.
An EU proposal to regulate e-cigarettes as a medicine was recently rejected, but in the UK e-cigarettes will be licensed as a medicine from 2016.
Healthy rats
E-cigarettes are still relatively new, so there is little in the way of long-term studies looking at their overall health impacts.
In order to have valid clinical data, a large group of e-cigarette users would need to be followed for many years.
Seeing as many users aim to stop smoking, following a large group of e-smokers for a long period could be difficult.
But in rats at least, a study showed that after they inhaled nicotine for two years, there were no harmful effects. This was found in a 1996 study before e-cigarettes were on the market, a study Dr Le Houezec said was reassuring.
Concern about the increase in e-cigarette use remains.
The World Health Organization advised that consumers should not use e-cigarettes until they are deemed safe. They said the potential risks "remain undetermined" and that the contents of the vapour emissions had not been thoroughly studied