Quitting cigarettes remains one of the most effective steps a person can take to reduce the risk of lung cancer. However, a major new study suggests that former smokers who continue using electronic cigarettes may not receive the same long-term protection as those who stop using both products.
Researchers analysed health records from more than 4.5 million adults in South Korea with a history of conventional cigarette smoking. Former smokers who reported daily vaping had higher rates of lung cancer and death from lung cancer than former smokers who did not use e-cigarettes.
The findings do not prove that vaping directly causes lung cancer, nor do they show that switching completely to e-cigarettes is as dangerous as continuing to smoke combustible cigarettes. They do raise an important concern: vaping after cigarette cessation may weaken some of the cancer-risk reduction gained by quitting.
What the 4.5-Million-Person Study Examined
The study, published in Nature Medicine, included 4,524,895 adults who participated in South Korea’s National Health Screening Program in 2018. Researchers also used earlier health-screening records from 2012 to 2014 to reconstruct participants’ smoking histories.
Participants were classified as current cigarette smokers, recent quitters or longer-term quitters. Daily e-cigarette use reported in 2018 was used to identify people who vaped after stopping conventional cigarettes.
The researchers followed participants through December 2023. Across more than 24.1 million person-years of observation, they recorded 35,887 lung cancer diagnoses and 12,807 deaths attributed to lung cancer.
The enormous sample gave researchers enough statistical power to investigate an outcome that can take many years to develop and remains relatively uncommon in any short period.
Former Smokers Who Vaped Had Higher Lung-Cancer Rates
Compared with former smokers who had stopped using both cigarettes and e-cigarettes, those who vaped after quitting had a 56 percent higher adjusted rate of developing lung cancer.
Their adjusted rate of death from lung cancer was approximately twice as high as that of complete quitters. The association appeared in both recent and longer-term quitters, although the size and certainty of the estimate varied between groups.
The relationship was particularly noticeable among people already considered at elevated risk because of age and accumulated cigarette exposure. In a subgroup aged 50 to 80 with at least 20 pack-years of smoking history, post-cessation vaping was associated with a 91 percent higher rate of lung cancer and a 92 percent higher rate of lung-cancer death compared with complete cessation.
A pack-year represents smoking an average of one pack per day for one year. Someone who smoked one pack daily for 20 years, or two packs daily for 10 years, would have a 20-pack-year history.
The Results Do Not Mean Vaping Erases Every Benefit of Quitting
The phrase “erases the gains from quitting” is more dramatic than the study’s actual conclusion.
The researchers stated that vaping may attenuate, or reduce, the lung-cancer prevention benefits associated with complete smoking cessation. They did not conclude that former smokers who vape receive no benefit at all from stopping cigarettes.
The study’s main figures were also relative comparisons. A 56 percent higher relative rate does not mean that 56 percent of former smokers who vape will develop lung cancer.
Individual risk depends heavily on age, total cigarette exposure, years since quitting, family history, occupational exposures, radon and other medical factors. The study did not create a personal prediction for any individual user.
It would also be incorrect to interpret the findings as a reason to return to combustible cigarettes. The FDA continues to describe cigarettes as the most harmful tobacco products because combustion exposes users to thousands of chemicals. E-cigarettes generally occupy a lower-risk category, although they are neither harmless nor comparable with approved nicotine-replacement treatment.
Why Vaping Could Affect Lung-Cancer Risk
Electronic cigarettes do not burn tobacco, so their aerosol typically contains fewer and lower levels of many toxic chemicals found in cigarette smoke. That difference is the basis for their potential role in reducing harm when an adult smoker switches completely.
However, e-cigarette aerosol is not simply water vapour. Depending on the product and how it is operated, users may inhale nicotine, ultrafine particles, metals, flavouring chemicals, carbonyl compounds and other substances capable of irritating or damaging lung tissue.
The FDA states that some chemicals linked to lung damage are present in e-cigarette aerosols and that more high-quality research is needed to determine their long-term effects. It also emphasises that prolonged dual use of cigarettes and e-cigarettes may produce harms similar to, or in addition to, cigarette smoking alone.
Laboratory evidence cited by the Nature Medicine researchers has identified mechanisms that could plausibly contribute to cancer, including DNA damage, impaired DNA repair, inflammation and exposure to carcinogenic compounds. These biological findings support concern but do not independently prove that vaping causes human lung cancer at a particular rate.
A Very Large Study Can Still Have Important Limitations
The study was observational. Researchers compared health outcomes among people who had already made different tobacco-use choices rather than randomly assigning anyone to vape or abstain.
That design cannot eliminate all alternative explanations. Former smokers who chose to vape may have previously smoked more intensely, found nicotine dependence harder to overcome or differed from complete quitters in ways that health records could not fully capture.
Researchers adjusted their analyses for known demographic, health and smoking-related factors, but residual confounding may remain. The authors therefore explicitly stated that causality could not be established.
Vaping status was also based on daily e-cigarette use reported at the 2018 baseline assessment. Participants may have stopped vaping, restarted smoking, changed products or altered their frequency during the following years. Those changes could lead to exposure misclassification.
The research was conducted in South Korea, where tobacco products, regulations and patterns of use may differ from those in the United States, United Kingdom and other countries. The results are highly important, but the exact risk estimates may not transfer perfectly to every population.
An accompanying assessment from the World Health Organization’s International Agency for Research on Cancer described the study as significant real-world evidence while emphasising that further research is needed to resolve remaining questions about long-term risk.
Complete Cessation Still Offers the Greatest Protection
The findings reinforce a distinction that can become lost in debates over whether vaping is safer than smoking.
For a person who currently smokes and cannot otherwise quit, switching completely to e-cigarettes may reduce exposure to many toxic chemicals. For a person who has already stopped smoking, continuing to inhale e-cigarette aerosol may introduce risks that complete abstinence would avoid.
The CDC reports that quitting smoking lowers the risks of cardiovascular disease, respiratory illness and 12 different cancers. The added risk of lung cancer falls by approximately half after 10 to 15 years compared with continued smoking, although it does not immediately return to that of someone who never smoked.
The new study suggests that continued vaping could reduce part of that long-term improvement, particularly in older adults with substantial past cigarette exposure.
E-Cigarettes Can Help Some Smokers Quit, but the End Goal Matters
Clinical trials and systematic reviews have found that nicotine-containing e-cigarettes can help some adults stop smoking, especially when accompanied by behavioural support. The new findings do not invalidate that evidence because helping someone stop cigarettes and assessing cancer risk years later are different research questions.
The results instead support a two-stage approach: first eliminate combustible cigarette smoking, then develop a realistic plan to stop vaping rather than allowing it to become a permanent replacement.
No e-cigarette has been approved by the FDA as a smoking-cessation medicine. FDA-approved nicotine-replacement products—including patches, gum and lozenges—deliver controlled nicotine without cigarette smoke or e-cigarette aerosol and can substantially increase the likelihood of successfully quitting when used correctly.
Abruptly abandoning vaping without support may lead some former smokers back to cigarettes. A clinician, pharmacist or tobacco-cessation specialist can help reduce nicotine gradually, manage withdrawal and select an appropriate approved treatment.
Former Smokers Should Not Panic Over Past Vaping
The study does not show that every former smoker who has vaped will develop lung cancer. Most participants did not receive a lung-cancer diagnosis during follow-up, and individual risk cannot be calculated from the headline percentages alone.
A former smoker who currently vapes should view the findings as a reason to work toward complete tobacco and nicotine cessation—not as evidence that previous progress has been lost permanently.
People with substantial smoking histories should also discuss lung-cancer screening eligibility with a healthcare professional. Screening recommendations are based primarily on age and cigarette pack-years, not on whether someone currently vapes, and the new study has not independently changed those guidelines.
The clearest conclusion remains consistent with decades of evidence: stopping cigarettes produces major health benefits, and avoiding continued exposure to other inhaled tobacco products is likely to offer the strongest long-term protection.
The 4.5-million-person study does not prove that vaping completely cancels the benefits of quitting. It does provide the strongest warning yet that replacing cigarettes with indefinite e-cigarette use may leave more lung-cancer risk than becoming completely tobacco-free.
