Published in the journal Carcinogenesis, the study evaluated a broad range of international research and brought together experts from several institutions, including The University of Queensland, Flinders University, The University of Sydney, Royal North Shore Hospital, The Prince Charles Hospital, and Sunshine Coast University Hospital.

The research team included specialists from multiple fields such as pharmacy, epidemiology, thoracic surgery, and public health. By examining evidence from a variety of scientific disciplines, they sought to determine whether vaping itself may contribute to cancer development.

"To our knowledge, this review is the most definitive determination that those who vape are at increased risk of cancer compared to those who don't," Prof. Stewart says.

The review focused on carcinogenicity, or cancer causation, and argues that while vaping has often been studied as a pathway to cigarette smoking, far less attention has been paid to the possibility that e-cigarettes could directly cause cancer on their own.

Researchers describe the work as one of the most extensive evaluations yet of whether vaping can increase cancer risk independently of traditional tobacco smoking. The analysis combined findings from clinical research, animal studies, and laboratory investigations involving chemicals generated by e-cigarettes.

"Considering all the findings -- from clinical monitoring, animal studies and mechanistic data -- e-cigarettes are likely to cause lung cancer and oral cancer," Prof. Stewart says.

Although the results were highly consistent across different areas of research, Prof. Stewart notes that the exact number of cancer cases attributable to vaping remains unknown.

"Our assessment is qualitative and does not involve a numerical estimate of cancer risk or burden. We'll only be able to determine the precise risk once longer-term studies are available."

Growing Concerns About Vaping and Public Health

E-cigarettes first entered the market in the early 2000s and became available in Australia around 2008. They were initially promoted as a potentially safer alternative to conventional cigarettes and as a tool to help people quit smoking.

Since then, brightly colored and flavored vaping products have become increasingly popular, especially among younger users. Despite tighter regulations introduced by the Australian Government in 2023, vaping remains common outside schools, bars, and train stations throughout the country. Current rules prohibit disposable and non-therapeutic vapes, while therapeutic vaping products can only be sold through pharmacies and only for smoking cessation purposes.

"E-cigarettes are known to be a gateway to smoking and hence cancer," says co-author UNSW Associate Professor Freddy Sitas.

"But the extent to which they may cause cancer in their own right has not received as much attention in research," he says.

"The evidence was remarkably consistent across fields," he says. "It dictated an unequivocal finding now, though human studies that estimate the risk will take decades to accumulate."

Evidence Points in the Same Direction

Scientists have spent more than a century studying the health effects of smoking. Although e-cigarettes are much newer, exposure to nicotine containing aerosols has already been associated with addiction, poisoning, inhalation injuries, and burns.

Because long-term population studies are still underway, researchers must currently rely on other forms of evidence to assess potential cancer risks from vaping.

The review identified multiple cancer causing substances in e-cigarette aerosols, including volatile organic compounds and metals released by heating coils.

Researchers also examined several other lines of evidence. These included biomarkers in people that indicate DNA damage, oxidative stress, and inflammation in tissues; mouse studies that resulted in lung tumors; and laboratory experiments showing cellular injury and disruptions to biological processes linked to cancer development.

According to the authors, the collective findings consistently point toward the same conclusion.

Dual Use May Increase Lung Cancer Risk

The researchers also highlight growing evidence that many smokers who switch to vaping continue using conventional cigarettes as well.

"Most of those who use e-cigarettes to quit smoking end up in 'dual-use-limbo', unable to shake off either habit," says A/Prof. Sitas.

"What we do know from recent epidemiological evidence from the USA is that those who both vape and smoke are at an additional four-fold increased risk of developing lung cancer."

Those findings were discussed in a separate commentary by A/Prof. Sitas and Prof. Stewart published in Cancer Epidemiology.

Researchers See Echoes of Smoking History

A/Prof. Sitas and Prof. Stewart say there are notable similarities between today's vaping debate and the early scientific investigation of smoking related diseases.

It took decades of research before smoking was officially recognized as a cause of lung cancer. Nearly a century passed between early observations in the mid-1800s and the landmark US Surgeon General's report in 1964.

During much of that period, warning signs were frequently ignored or dismissed.

"Early reports linked smoking to infectious diseases such as tuberculosis, followed by cardiovascular disease, stroke and lung cancer," A/Prof Sitas says.

He says the same pattern may now be unfolding with vaping -- and that researchers should not repeat the delay that occurred with cigarettes.

"E-cigarettes were introduced about 20 years ago. We should not wait another 80 years to decide what to do."