Annex | Scientific Studies on Vaping and Tobacco

Scientific studies on vaping: evidence, harm reduction and comparison with tobacco

Expanded compendium of the main studies, systematic reviews and public body positions on electronic cigarettes, smoking cessation, biomarkers, dual use and relative risk compared with combustible tobacco.

0. Key notices before discussing “studies”

This page is designed so you can read the evidence critically: what type of study it is, what exactly it measures and what conclusions can (and cannot) be drawn.

1. Quick evidence map (what we know best today)

In science, not all studies carry the same weight. This map prioritises systematic reviews, clinical trials and public body reports.

Toxicity scale: direct comparison

A study published in the Journal of Hazardous Materials by the Pasteur Institute of Lille analysed levels of carbonyls and hydrocarbons (PAHs):

The study concludes that electronic cigarettes reduce the toxicant dose per µg of nicotine delivered (see cited article). ^[10]

2. What public bodies say (and why it matters)

2.1 United Kingdom: harm reduction approach (evidence reports)

The United Kingdom is one of the countries with the strongest production of public-health applied evidence on vaping as a tool for adult smokers. Two key pieces:

• OHID (UK Government) – “Vaping in England: evidence update” (2022): synthesis of studies on prevalence, cessation, toxicant exposure and relative risks. ^[1]
• Royal College of Physicians – “E-cigarettes and harm reduction” (2024 update): evidence review and clinical/policy recommendations. ^[5]

2.2 Public Health England and the “95%” communication

The phrase “around 95% less harmful” comes from reviews by Public Health England as a way to communicate much lower relative risk compared with combustible tobacco. It is important to understand it as a guiding estimate, not as an exact and immutable figure. ^[2]–[4]

2.3 WHO: “not harmless” and priority on youth prevention

The World Health Organization maintains a precautionary position: it recognises that the products are not risk-free, emphasises the protection of minors/non-smokers and reinforces that the safest option is not to use either (neither tobacco nor vaping). ^[12]–[13]

3. Studies on quitting smoking: systematic reviews and clinical trials

3.1 Cochrane review (living review): the “gold standard” in evidence synthesis

The Cochrane “living” systematic review is updated with new trials. In practical terms, it is one of the most useful sources for answering the question: do nicotine e-cigs help people quit smoking? ^[6]

3.2 Highlighted clinical trial (NEJM): e-cig vs nicotine replacement therapy

The trial published in The New England Journal of Medicine compared nicotine e-cigarettes with NRT in a cessation service setting, providing a widely cited piece for the public debate. ^[8]

3.3 Practical conclusion (for adult smokers)

The useful evidence for the reader is this: if the goal is to quit tobacco, results tend to be better when there is complete switching, a realistic nicotine strategy and (minimal) habit/environment support. ^{[1], [5]–[8]}

4. Comparative toxicology: what “hard” studies measure (smoke vs aerosol)

4.1 Why smoking is so harmful (combustion changes the game)

Scientific comparison usually starts with the mechanism: combustible tobacco produces smoke through combustion (high temperatures and complex reactions), while vaping produces an aerosol by heating an e-liquid (without combustion). That does not mean “harmless”, but it does drastically change the emissions and exposure profile. ^{[1], [5], [10]}

4.2 Biomarkers: when science looks at the body (not just vapour)

In addition to measuring aerosol, many reviews prioritise studies that measure biomarkers of exposure to observe whether switching from smoking to vaping reduces exposure to compounds typical of tobacco. ^{[1], [5], [15]}

4.3 What a toxicity study “does not” prove

• That something has fewer toxicants than smoke does not prove “absence of risk”. ^[12]–[13]
• The reduction of toxicants usually supports the concept of lower relative risk, but final clinical harm depends on sustained exposure, history and individual vulnerabilities. ^{[5], [15]}

5. Dual use (smoking + vaping): why it is the big nuance

From a harm reduction perspective, the health goal is to reduce exposure to combustion. With dual use, exposure to smoke still exists, so the expected benefit tends to be smaller than with complete replacement. ^{[1], [5]}

5.2 Practical conclusion

• If you keep smoking, tobacco continues to dominate the risk.
• Reducing cigarettes is better than nothing, but the big step is usually leaving combustion behind.
• Dual use studies help avoid the simplistic message: “vaping = automatic benefit”. ^{[9], [14]}

6. Respiratory and cardiovascular health: what is known, what is debated and what is missing

6.1 The real problem: “biological harm” vs “long-term clinical harm”

Many studies show reduced exposure to toxicants compared with smoke (toxicology/biomarkers). The more difficult question is whether that reduction translates into less disease in the long term across large populations. ^{[5], [15]}

6.2 Umbrella reviews and broad reviews (overview)

Umbrella reviews help map the full field. One example (ScienceDirect, 2024) reviews evidence on e-cig use, dual use and other patterns. ^[11]

6.3 Responsible reading for the user

• If a study compares vapers with non-smokers, it is normal to find higher risks (the ideal reference point is “zero exposure”). ^[12]–[13]
• If it compares complete switching vs continued smoking, the key question is whether it reduces exposure to combustion and improves cessation capacity. ^{[1], [5]–[8]}
• In observational studies, smoking history can distort results; this is why reviews insist on separating “ex-smoker who vapes” from “dual smoker”, etc. ^{[5], [9], [14]}

Bibliographic references

1. Office for Health Improvement and Disparities (OHID). (2022). Vaping in England: evidence update (August 2022). GOV.UK. Official link.
2. Public Health England (PHE). (2015). E-cigarettes around 95% less harmful than tobacco estimates: landmark review. GOV.UK (press release). Official link.
3. McNeill, A., Brose, L. S., Calder, R., Hitchman, S. C., & Hajek, P. (2015). E-cigarettes: an evidence update (Report commissioned by Public Health England). London: PHE. PDF.
4. McNeill, A., Hajek, P., et al. (2015). Underpinning evidence for the estimate that e-cigarette use is around 95% safer than smoking. PDF.
5. Royal College of Physicians. (2024). E-cigarettes and harm reduction: An evidence review (updated full report). London: RCP. PDF.
6. Lindson, N., Butler, A. R., McRobbie, H., et al. (Living systematic review; latest update available in Cochrane Library). Electronic cigarettes for smoking cessation (Cochrane Database of Systematic Reviews; CD010216). Cochrane Library.
7. Centre for Evidence-Based Medicine (CEBM), University of Oxford. (n.d.). Living Evidence: Electronic cigarettes for smoking cessation (briefings & updates). Updates page.
8. Hajek, P., Phillips-Waller, A., Przulj, D., et al. (2019). A randomized trial of e-cigarettes versus nicotine-replacement therapy. The New England Journal of Medicine, 380, 629–637. doi:10.1056/NEJMoa1808779. Text.
9. NEJM Evidence. (2024). Population-based disease odds / dual use and e-cigarette use. Article.
10. Dusautoir, R., Zarcone, G., Verriele, M., et al. (2020). Comparison of tobacco cigarette, heated tobacco product (IQOS), and e-cigarette aerosol emissions. Journal of Hazardous Materials. (ScienceDirect: S0304389420314060). Article.
11. ScienceDirect. (2024). E-cigarette use, dual use, and other tobacco use: Umbrella review. Article.
12. World Health Organization (WHO). (n.d.). Tobacco: E-cigarettes (Q&A). WHO page.
13. World Health Organization (WHO). (2024). Regulation of e-cigarettes (document repository). PDF.
14. Nicotine & Tobacco Research. (2025). Association of exclusive and dual use of e-cigarettes with disease outcomes (observational analysis). (Access via PubMed/Journal). PubMed.
15. National Academies of Sciences, Engineering, and Medicine. (2018). Public health consequences of e-cigarettes. Washington, DC: The National Academies Press. Report.

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