Scientists found that e-cigarettes, marketed for years as the safe exit from smoking, are linked to significantly higher lung cancer risk in people who use them after quitting
E-cigarettes have been marketed and widely understood as the safer exit ramp from smoking, the thing you switch to so you can eventually quit nicotine entirely without going back to tobacco. A study published in Nature Medicine this month, the largest of its kind, followed more than 4.5 million adults with a smoking history in South Korea for up to a decade and found that people who quit cigarettes but kept vaping had a meaningfully higher risk of developing and dying from lung cancer than people who quit smoking and stayed away from e-cigarettes entirely.
The research team, based at Seoul National University, used South Korea’s national health screening program to track 4,524,895 adults with a conventional smoking history starting from a 2018 baseline, with smoking and vaping records going back to 2012. Participants were sorted by whether they were current smokers, recent quitters, or long-term quitters, and whether they used e-cigarettes daily. Over more than 24 million person-years of follow-up through the end of 2023, the study recorded 35,887 lung cancer diagnoses and 12,807 lung cancer deaths.
What the comparison actually showed
The key comparison in the study wasn’t smokers versus non-smokers. It was ex-smokers who vaped versus ex-smokers who didn’t. Compared with people who quit cigarettes completely and didn’t take up e-cigarettes, those who quit smoking but used e-cigarettes daily had a 56 percent higher risk of developing lung cancer and a similarly elevated risk of dying from it.
This is the comparison that matters for the millions of people who’ve already made the switch believing they’d reduced their risk. The study isn’t saying vaping is as dangerous as continuing to smoke, current smokers still carried the highest risk of all in the data. It’s saying that the specific decision many people made, swap cigarettes for vaping as a permanent replacement rather than a bridge to quitting nicotine altogether, didn’t get them back to the risk level of someone who quit and stayed quit.
Why this contradicts the “harm reduction” framing
E-cigarettes don’t contain tobacco, and the aerosol they produce is chemically different from cigarette smoke. That’s the basis for the harm reduction argument that has shaped public health messaging and personal decisions for over a decade. But the aerosol from e-cigarettes still contains carbonyl compounds, including formaldehyde, acetaldehyde, and acrolein, along with toxic metals like chromium, nickel, and lead, all of which have established links to cancer. The absence of tobacco doesn’t mean the absence of carcinogenic exposure.
What the new data adds to this picture is scale and duration. Smaller and shorter studies have raised this concern before, including earlier work from some of the same research group presented at a 2024 conference using a partial version of this dataset. The new Nature Medicine paper extends the cohort to its full size and follow-up period, and the size of the study, over 4.5 million people followed for years, makes it much harder to dismiss the pattern as noise or as confined to a particular subgroup of heavy users.
What this means for someone who already made the switch
The honest framing here isn’t that switching to vaping was worse than continuing to smoke. Continued smoking still carried the highest absolute risk in this data, as it does in essentially every study of its kind. The finding is narrower and in some ways more uncomfortable: among the large group of people who did the hard work of quitting cigarettes, the subset who used e-cigarettes as their replacement ended up with worse outcomes than the subset who quit nicotine altogether.
For public health messaging, this complicates a story that’s been told fairly simply for years, that e-cigarettes are a reasonable harm-reduction tool for people who can’t or won’t quit nicotine outright. The researchers themselves frame their conclusion carefully: when health systems design smoking cessation interventions, the potential harms of e-cigarettes as a long-term substitute need to be weighed against their use, rather than treated as a costless alternative to cigarettes.
What the study can’t tell us
This is an observational study, not a randomized trial, so it can’t fully rule out the possibility that people who choose to keep vaping after quitting differ in other ways, perhaps in nicotine dependence severity, other health behaviors, or underlying risk factors, that also affect lung cancer risk. The Korean population and smoking patterns also may not translate directly to other countries with different tobacco and vaping product regulations and use patterns.
What the study does add, given its size and the consistency of the pattern across years of follow-up, is a much stronger version of a concern that smaller studies had only been able to suggest. For the large number of people worldwide who quit cigarettes specifically by switching to e-cigarettes, and who have settled into vaping as a long-term habit rather than a temporary bridge, this data is the most concrete reason yet to revisit that assumption.
Sources:
Kim, Y.W., et al.
Electronic cigarette use after smoking cessation and lung cancer risk.
Nature Medicine, 2026.
nature.com/articles/s41591-026-04469-5
dbrecoveryresources.com/2026/06/e-cig-use-after-quitting-lung-cancer
