Vaping could seriously damage your lungs, scientists have now warned.
Inhaling nicotine vapours was thought to be less harmful than smoking cigarettes .
But according to a study in the medical journal Thorax, the vapour can impede the alveolar macrophages, the cells which remove bacteria, allergens, dust and other potentially harmful particles from the lungs.
The scientists, from Birmingham University, say people who vape can end up with similar symptoms to those of smokers and people with COPD (chronic obstructive pulmonary disease).
Lead author of the study, Prof David Thickett, said: "I don't believe e-cigarettes are more harmful than ordinary cigarettes.
"But we should have a cautious scepticism that they are as safe as we are being led to believe."
He added: "In terms of cancer causing molecules in cigarette smoke, as opposed to cigarette vapour, there are certainly reduced numbers of carcinogens.
"They are safer in terms of cancer risk, but if you vape for 20 or 30 years and this can cause COPD, then that's something we need to know about."
Many studies have focused on the chemical make-up of e-cigarette liquid before it is vaped, the researchers said.
However, they developed a procedure to mimic vaping in the laboratory, testing the effect of e-cigarette vapour condensate on alveolar macrophages extracted from the lung tissue samples of eight non-smokers.
The condensate was found to be more harmful to the cells than plain e-cigarette fluid, and the effects worsened as the "dose" was increased.
The researchers said further work is needed to fully understand the effects of vapour exposure in humans, but added: "We suggest continued caution against the widely held opinion that e-cigarettes are safe."
Commenting on the findings, Professor John Britton, director of the UK Centre for Tobacco and Alcohol Studies at the University of Nottingham, told the Mirror : "This study demonstrates evidence that lung cells exposed to electronic cigarette vapour become inflamed, as would be expected given that electronic cigarette vapour contains oxidant and other pro-inflammatory constituents.
"This indicates that long-term use of electronic cigarettes is likely to have adverse effects, as is widely recognised by leading health authorities in the UK including the Royal College of Physicians and Public Health England.
"However, since electronic cigarettes are used almost exclusively in the UK by current or former smokers, the key question is how this adverse effect compares with that of exposure to cigarette smoke."
He added: "The harsh truth is that smoking kills, and smokers who switch completely to electronic cigarettes are likely to substantially reduce the likelihood of premature death and disability."
