Vaping could raise the risk of lung and mouth cancer, researchers have warned.
Vaping
Scientists from the University of New South Wales, in Australia, have cast fresh doubt on the safety of e-cigarettes - which have often been marketed as a safer alternative to smoking.
The team reviewed a series of studies, including experiments in mice that developed lung tumours after exposure to vape aerosol, alongside reports of heavy users who went on to develop aggressive mouth cancer.
Their findings suggest that chemicals in e-cigarette vapour may damage DNA and trigger inflammation - two key processes linked to cancer development.
Lead author Professor Bernard Stewart said the full extent of the risk is still unclear.
He explained: "We’ll only be able to determine the precise risk once longer-term studies are available."
However, the findings have sparked backlash from other experts, who argue the evidence is not strong enough to draw conclusions about cancer risk.
Professor Lion Shahab, of University College London, said: "No one would argue that e-cigarettes are entirely risk-free.
"They should be used as a harm reduction product to help those who smoke to quit and reduce their risk of developing smoking-related diseases.
"However, this review does not offer a ‘smoking gun’ that e-cigarettes cause oral or lung cancer, nor does it make an attempt at quantifying this risk.
"The evidence is simply not there."