NEW YORK (BLOOMBERG) -- E-cigarettes are likely to cause cancer, including in the lungs and mouth, according to a sweeping review of scientific evidence that challenges their positioning as a safer alternative to smoking.
Published Monday in the journal Carcinogenesis, the review concludes that nicotine-based vapes are “likely to be carcinogenic to humans,” even though long-term population studies are still lacking.
“Considering all the findings — from clinical monitoring, animal studies and mechanistic data — e-cigarettes are likely to cause lung cancer and oral cancer,” said Bernard Stewart, a cancer researcher at Sydney’s University of New South Wales, who led the study.
The findings add to growing scrutiny of a vaping industry worth about $30 billion to $46 billion globally, with implications for tobacco groups that have invested heavily in e-cigarettes, including Altria Group Inc., British American Tobacco Plc and Imperial Brands Plc. They could also complicate public health strategies that have embraced them as a harm-reduction tool for smokers.
Cancer Harms
The review also challenges policies that have embraced vaping as a harm-reduction strategy and add to calls from cancer specialists for tighter regulation of e-cigarettes. Countries including New Zealand — and the UK, which has encouraged smokers to switch — have backed e-cigarettes to help smokers quit, but the new analysis raises questions about whether those approaches underestimate long-term health risks.
Unlike many earlier studies, which compared vaping with smoking, the review focused on whether e-cigarettes could cause cancer in their own right. Researchers examined clinical data, lab experiments and animal studies, rather than waiting for decades of epidemiological evidence.
The approach reflects a key challenge: e-cigarettes have only been widely used for about 20 years, meaning definitive proof based on long-term human outcomes could take decades. Instead, the authors relied on biomarkers — early biological changes linked to cancer. Studies show people who vape absorb nicotine-related compounds, heavy metals and other chemicals that can damage DNA and trigger inflammation, hallmarks of cancer development.
“There is no doubt that the cells and tissues of the oral cavity — the mouth — and the lungs are altered by inhalation from e-cigarettes,” Stewart said during a media briefing.
Animal studies cited in the review add to the concern. In one experiment, mice exposed to e-cigarette aerosols developed lung tumors at far higher rates than control groups, along with changes in the bladder linked to cancer.
The evidence isn’t yet precise enough to quantify the risk. “Our assessment is qualitative and does not involve a numerical estimate of cancer risk or burden,” Stewart said.
Even so, the evidence points in one direction, the authors said. Reviews published over the past decade have shifted from uncertainty to increasing concern about carcinogenic effects.
Dual Use
The findings also highlight a growing problem for regulators: Many users don’t fully switch from cigarettes to vaping, but instead use both. That phenomenon — often referred to as “dual use” — is common, with more than half of users unable to quit either habit, according to the researchers.
“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,” said co-author Freddy Sitas, an epidemiologist at UNSW.
For public health officials, the paper draws uncomfortable parallels with the early history of tobacco research. It took decades for scientists to conclusively prove that smoking causes lung cancer, despite mounting early warning signs. The authors argue that the same mistake should not be repeated with vaping, particularly given its rapid uptake among young people.
“We should not wait another 80 years to decide what to do,” Sitas said.
Health experts said the findings shouldn’t be interpreted as a reason for smokers to return to cigarettes, which remain far more harmful.
“We’ve always assumed that vapes are safer than cigarettes, but what we are showing is that they might not be safe after all,” Sitas said.
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