ENDS Respiratory System

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Studies, Surveys, Papers, and Case Studies

  • Sometimes it's necessary to view the PDF version to access the full study.
  • This page is for referencing the possible benefits of ENDS products vs. smoking cigarettes from a Respiratory System standpoint. (Electronic Nicotine Delivery Systems are also known as vapor technology, ecigarettes, ecigs, EVP, etc.)
  • If you'd prefer someone else to add a study to a topic, there is a subject section called "Suggested studies to add to this page". You may put the link in that section for one of the regular page editors to address.
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2021: Effect of an electronic nicotine delivery system with 0, 8, or 36 mg/mL liquid nicotine versus a cigarette substitute on tobacco-related toxicant exposure: a four-arm, parallel-group, randomised, controlled trial

Use of an ENDS with cigarette-like nicotine delivery can reduce exposure to a major pulmonary carcinogen, NNAL, even with concurrent smoking.

2020: Benefits of e-cigarettes in smoking reduction and in pulmonary health among chronic smokers undergoing a lung cancer screening program at 6 months

The study is a double-blind randomized controlled trial. Two hundred and ten smokers were randomized into three groups: nicotine e-cigarette (8 mg/mL nicotine concentration), nicotine-free e-cigarettes (placebo), and control with 1:1:1 ratio. All participants received a 3 months cessation program that included a cognitive-behavioral intervention aimed at supporting people in changing their behavior and improving motivation to quit. After 6 months about 20% of the entire sample stopped smoking. Participants who used e-cigarettes with nicotine smoked fewer tobacco cigarettes than any other group after 6 months. Our data add to the efficacy and safety of e-cigarettes in helping smokers reducing tobacco consumption and improving pulmonary health status. Pulmonary health, assessed with self-reported measures, clinical evaluations and the Leicester Cough Questionnaire, improved in participants who stopped smoking compared to their own baseline. Moreover, participants in this group [nicotine e-cigarettes] showed the lowest level of exhaled carbon monoxide, and the lowest level of dependence compared to the nicotine-free e-cigarette and control conditions.

2020: E-Cigarettes and Respiratory Disease: A Replication, Extension, and Future Directions

  • The statistical associations between e-cigarette use and respiratory disease are driven by e-cigarette users who are also current or former smokers of combustible tobacco.
  • A striking feature of the data is that almost all e-cigarette users were either current or former smokers of combustible tobacco.
  • Among respondents who had never smoked combustible tobacco, we find no evidence that current or former e-cigarette use is associated with respiratory disease.

Link to PDF

2020: Exclusive e-cigarette users report lower levels of respiratory symptoms relative to dual e-cigarette and cigarette users

Findings suggest that differences in respiratory symptoms between dual and exclusive e-cigarette users appear to be attributable to combustible cigarette smoking, rather than more intense or frequent e-cigarette use across groups.

2020: Investigation on the antibacterial activity of electronic cigarette liquids (ECLs): a proof of concept study

  • Our results have shown that flavors considerably enhance antibacterial activity.
  • This study provides important evidence that should be taken into consideration in further investigative approaches, to clarify the different sensitivity of the various bacterial species to e-liquids, including the respiratory microbiota, to highlight the possible role of flavors and nicotine.
  • Citation: Virginia Fuochi, Massimo Caruso , Rosalia Emma, Aldo Stivala, Riccardo Polosa, Alfio Distefano and Pio Maria Furneri *, “Investigation on the Antibacterial Activity of Electronic Cigarette Liquids (ECLs): A Proof of Concept Study”, Current Pharmaceutical Biotechnology (2020) 21: 1. doi:10.2174/1389201021666200903121624


Ex-smokers who have switched to exclusive regular use of combustion-free nicotine delivery systems (i.e. ECs/e-cigarettes and HTPs/heated tobacco products) exhibit similar saccharin transit time as never and former smokers. This suggests that combustion-free nicotine delivery technologies are unlikely to have detrimental effects on MCC (mucociliary clearance) function

2020: COPD smokers who switched to e-cigarettes: health outcomes at 5-year follow up

The present study suggests that EC use may ameliorate objective and subjective COPD outcomes, and that the benefits gained appear to persist long term. EC use for abstinence and smoking reduction may ameliorate some of the harm resulting from tobacco smoking in COPD patients.

2020: Cancer potencies and margin of exposure used for comparative risk assessment of heated tobacco products (HTPs) and electronic cigarettes (ECs) aerosols with cigarette smoke

(PDF 16 pages) Even if they should not be considered as risk-free products, however, HTPs and ECs lead to an appreciable risk reduction in comparison to cigarettes, both for cancer and non-cancer diseases. According to the current knowledge, and more specifically to the data presented here, HTPs and ECs might be considered as an acceptable reduced risk substitute for cigarettes for legal-age smokers who would otherwise continue smoking cigarettes. A more pronounced cancer risk reduction was observed when comparing the mean lifetime cancer risk for the considered ECs with that for cigarette smoke. This reduction was about two orders of magnitude (ratio of 0.009 and 0.014) with 2.42·10–4 and 3.95·10–4 for ECs compared to 2.73·10–2 for cigarettes. In terms of consumers, this would mean that 1 out of 36 cigarette smokers vs. 1 out of 4132 or 1 out of 2531 EC consumers may develop a cancer if the cancer root cause would be only associated with exposure to the considered HPHCs.

2020: Vaping effects on asthma: results from a web survey and clinical investigation

Almost all of the asthmatics who previously smoked would recommend switching to e-cig, and vaping did not worsen their asthma symptoms. Furthermore, switching from tobacco smoking to e-cigs showed a significant improvement in asthma control and quality of life, not showing, in the period studied, to affect pulmonary function tests. PDF Version

2019: The effect of e-cigarette aerosol emissions on respiratory health: a narrative review.

Expert opinion: There is growing evidence to support the relative safety of E-Cigarette (EC) emission aerosols for the respiratory tract compared to tobacco smoke. Public Health England estimated, on the basis of a review of 185 studies, that vaping an e-cigarette is likely to be at least 95% less harmful than smoking a regular cigarette. In 2016, the Royal College of Physicians reaffirmed this figure, estimating the risk of long-term inhalation of e-cigarette aerosol to be unlikely to exceed 5% of the risk associated with long-term cigarette smoking. This review article shows that although some potential effects on respiratory cell types can be shown in vitro, and low levels of chronic irritation of the respiratory tract can be anticipated at certain levels of vaping, these effects are much less than those of smoking. The clinical evidence confirms that ECs are unlikely to raise significant health concerns for the respiratory tract under normal conditions of use. Former smokers using and smokers intending to use ECs as a substitute for smoking should receive correct information about residual risks and potential benefits of these products. Promoting further access to ECs may offer an opportunity to reduce or prevent some of the otherwise inevitable burden of respiratory morbidity and mortality caused by tobacco smoking In an Expert Review in Respiratory Medicine article published about 7 years ago [Caponnetto P, Campagna D, Papale G, et al. The emerging phenomenon of electronic cigarettes. Expert Rev Respir Med. 2012 Feb; 6(1):63–74.., we discussed several important research developments and future avenues for e-cigarette science. In the authors’ view, those expert opinions have been substantiated by the growing body of evidence. We therefore reiterate our prediction that EC use is the most effective method of substituting tobacco cigarettes for those smokers who are unable or unwilling to quit and we are now confident that current vaping products are much less harmful than conventional cigarettes as well as earlier EC designs.

2018: Health effects in COPD smokers who switch to electronic cigarettes: a retrospective-prospective 3-year follow-up

The present study suggests that EC use may ameliorate objective and subjective COPD outcomes and that the benefits gained may persist long-term. EC use may reverse some of the harm resulting from tobacco smoking in COPD patients

2017: Health impact of E-cigarettes: a prospective 3.5-year study of regular daily users who have never smoked

In a small sample of young-adult never-smoking, daily EC users who were carefully followed for approximately 3½ years, we found no decrements in spirometric indices, development of respiratory symptoms, changes in markers of lung inflammation in exhaled air or findings of early lung damage on HRCT, when compared with a carefully matched group of never-smoking non-EC users. Even the heaviest EC users failed to exhibit any evidence of emerging lung injury as reflected in these physiologic, clinical or inflammatory measures. Moreover, no changes were noted in blood pressure or heart rate. Since the EC users who we studied were never smokers, potential confounding by inhalation of combustion products of tobacco were obviated.

2017: E-cigarettes in patients with COPD: current perspectives

Although ECs are not risk free, they are much less harmful than conventional tobacco smoking. The emerging clinical evidence suggests that ECs are unlikely to raise significant health concerns for the respiratory tract under normal conditions of use, even in smokers with preexisting lung disease. In particular, recent studies in COPD and chronic asthma suggest that substitution of conventional tobacco cigarettes for ECs can ameliorate subjective and objective disease-related outcomes and exacerbation rates as well as improving success in abstaining from smoking long term.

2017: Reduced biological effect of e-cigarette aerosol compared to cigarette smoke evaluated in vitro using normalized nicotine dose and RNA-seq-based toxicogenomics

Here, we assessed the transcriptional response of a primary 3D airway model acutely exposed to e-cigarette aerosol and cigarette (3R4F) smoke. Based on equivalent or higher nicotine delivery, an acute exposure to e-cigarette aerosol had a reduced impact on gene expression compared to 3R4F smoke exposure in vitro. Therefore, we can conclude that the data strongly supports the adverse effect of acute exposure to cigarette smoke on MucilAir™ cells with functional enrichment for cancer, inflammation and fibrosis genes. In contrast, RNA-seq-based toxicogenomics showed a reduced impact of e-cigarette aerosols acute exposure on MucilAir™ cells compared with 3R4F reference cigarette at equivalent or higher dose of nicotine exposure.

2017: Electronic cigarette vapor alters the lateral structure but not tensiometric properties of calf lung surfactant

While both e-cigarette vapor and conventional cigarette smoke affect surfactant lateral structure, only cigarette smoke disrupts surfactant interfacial properties. The surfactant inhibitory compound in conventional cigarettes is tar, which is a product of burning and is thus absent in e-cigarette vapor.

2017: Comparing the cancer potencies of emissions from vapourised nicotine products including e-cigarettes with those of tobacco smoke

(PDF 8 pages) “Most e-cigarette analyses indicate cancer potencies <1% that of tobacco smoke and <10% that of a heat-not-burn prototype, although a minority of analyses indicate higher potencies.” Optimal combinations of device settings, liquid formulation and vaping behaviour normally result in e-cigarette emissions with much less carcinogenic potency than tobacco smoke. Article in Lung Disease News: E-Cigarettes Carry Much Less Risk of Lung Cancer Than Cigarette Smoke, Study Finds

2017: Have combustible cigarettes met their match? The nicotine delivery profiles and harmful constituent exposures of second-generation (G2) and third-generation (G3) electronic cigarette users

(PDF 6 pages) While not harmless, electronic cigarettes (e-cigarettes) have demonstrated a much more favourable toxicological profile than combustible cigarettes—the worldwide leading cause of preventable death. Average eCO levels (ppm) were significantly higher in smokers than in e-cigarette users. Compared with cigarettes, G2 and G3 e-cigarettes resulted in significantly lower levels of exposure to a potent lung carcinogen and cardiovascular toxicant.

2016: Evidence for harm reduction in COPD smokers who switch to electronic cigarettes (EC’s)

Conclusion: “These findings suggest that ECs use may aid smokers with COPD reduce their cigarette consumption or remain abstinent, which results in marked improvements in annual exacerbation rate as well as subjective and objective COPD outcomes.”

2016: Changes in the Frequency of Airway Infections in Smokers Who Switched to Vaping: Results of an Online Survey

Results: “Altogether 941 responses were received. Overall, 29% of responders reported no change in respiratory symptoms, 5% reported worsening, and 66% reported an improvement (95% CI=62.9-69.0).”

2016: Persisting long term benefits of smoking abstinence and reduction in asthmatic smokers who have switched to electronic cigarettes

This prospective study confirms that EC use ameliorates objective and subjective asthma outcomes and shows that these beneficial effects may persist in the long term. EC use can reverse harm from tobacco smoking in asthma patients who smoke. The evidence-based notion that substitution of conventional cigarettes with EC is unlikely to raise significant respiratory concerns, can improve counseling between physicians and their asthmatic patients who are using or intend to use ECs.

2016: Changes in breathomics from a 1‐year randomized smoking cessation trial of electronic cigarettes

Conclusion: “Smokers invited to switch to electronic cigarettes who completely abstained from smoking showed steady progressive improvements in their exhaled breath measurements and symptom scores. FeNo and eCO normalization is highly supportive of improved respiratory health outcomes and adds to the notion that quitting from tobacco smoking can reverse harm in the lung.”

2016: Changes in the Frequency of Airway Infections in Smokers Who Switched To Vaping: Results of an Online Survey

The switch from smoking to vaping was associated with a reduced incidence of self-reported respiratory infections.

2016: Respiratory infections and pneumonia: potential benefits of switching from smoking to Vaping

Also, given that the propylene glycol in EC aerosols is a potent bactericidal agent, switching from smoking to regular vaping is likely to produce additional lung health benefits. In conclusion, smokers who quit by switching to regular ECs use can reduce risk and reverse harm from tobacco smoking. Innovation in the e-vapour category is likely not only to further minimise residual health risks, but also to maximise health benefits.

2016: Patients with lung cancer: Are electronic cigarettes harmful or useful?

(must pay to view PDF) Based on current knowledge, for patients with lung or other forms of cancer who would otherwise continue to smoke, e-cigarettes offer an alternative way to quit smoking while they undergo medical treatment. The option to switch to e-cigarettes should be considered by healthcare practitioners with patients with cancer who would otherwise continue to smoke.

2014: Effect of Smoking Abstinence and Reduction in Asthmatic Smokers Switching to Electronic Cigarettes: Evidence for Harm Reversal

The e-cig may help smokers with asthma to reduce their cigarette consumption or remain abstinent and hence reduce the burden of smoking-related asthma symptoms. The positive findings observed with e-cigs allows us to advance the hypothesis that these products may be valuable for smoking cessation and/or tobacco harm reduction also in asthma patients who smoke. By substantially reducing number of cigarettes smoked per day and exposure to their hazardous toxicants, e-cigs may not only improve asthma symptoms and pulmonary function but may also confer an overall health advantage in smokers with asthma [13]. Therefore, e-cig use in asthmatic smokers unable or unwilling to quit should be exploited as a safer alternative approach to harm-reversal (i.e., specific reversal of asthma-related outcomes) and, in general, to harm-reduction (i.e., overall reduction of smoke-related diseases).


2021: Vaping Demystified

Yorkshire Cancer Research Through research and interviews with experts, we explore the truth about vaping and whether misconceptions are preventing us from reducing the largest preventable cause of cancer in Yorkshire.

2nd Hand Vapor

2022: Computational modeling method to estimate secondhand exposure potential from exhalations during e-vapor product use under various real-world scenarios

  • Acetaldehyde and acrolein were not detectable after use of any of the test products.
  • When these data were used as inputs to a computational room air level and non-user intake model, the ambient concentrations of exhaled nicotine and formaldehyde predicted that non-user intakes were substantially reduced for test product use compared to conventional cigarette use.
  • Collectively, the results predict that room air levels and exposure of the selected analytes to non-users were relatively low and several-fold below regulatory PELs and AIHA limit under the modeled space and use conditions.
  • ...room air levels of nicotine, formaldehyde, acrolein, and acetaldehyde levels were significantly below OSHA PELs or American Industrial Hygiene Association (AIHA) limit...

2018: Characterization of the Spatial and Temporal Dispersion Differences Between Exhaled E-Cigarette Mist and Cigarette Smoke

For both product categories, the particle concentrations registered following each puff were in the same order of magnitude. However, for e-cigarettes the particle concentration returned rapidly to background values within seconds; for conventional cigarettes it increased with successive puffs, returning to background levels after 30–45 minutes. Unlike for the e-cigarette devices tested, such temporal variation was dependent on the room ventilation rate. Particle size measurements showed that exhaled e-cigarette particles were smaller than those emitted during smoking conventional cigarettes and evaporated almost immediately after exhalation, thus affecting the removal of particles through evaporation rather than displacement by ventilation.

2017 Evaluation of Chemical Exposures at a Vape Shop

  • We collected air samples for flavoring chemicals (diacetyl, 2,3-pentanedione, 2,3-hexanedione, acetaldehyde, and acetoin), nicotine, formaldehyde, and propylene glycol.
  • Concentrations of vaping-related chemicals in our air samples were below occupational exposure limits.
  • Citation: NIOSH 2017. Evaluation of chemical exposures at a vape shop. By Zwack LM, Stefaniak AB, LeBouf RF. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Health Hazard Evaluation Report 2015-0107-3279

2017 Dr. Michael Siegel - Vape Shop Air Sampling by California State Health Department Suggests that Second Hand Vape Exposure is Minimal

This study, although conducted under very high exposure conditions in a small, non-ventilated vape shop with many employees and customers vaping and clouds of vapor visible, did not document any dangerous levels of exposure to any hazardous chemical. Nicotine exposure was essentially non-existent. Formaldehyde exposure was no different than in many indoor and outdoor environments at baseline. Acetone, acetoin, other aldehydes, toluene, benzene, and xylene were not detected. Chemicals that have been associated with "popcorn lung" were also not detected by the standard method. This study adds to the evidence that under real-life conditions, "secondhand vaping" does not appear to pose any significant health risks.

2014: Peering through the mist: systematic review of what the chemistry of contaminants in electronic cigarettes tells us about health risks

Threshold Limit Values (TLVs), were conducted under “worst case” assumptions about both chemical content of aerosol and liquids as well as behavior of vapers. There was no evidence of potential for exposures of e-cigarette users to contaminants that are associated with risk to health at a level that would warrant attention if it were an involuntary workplace exposures. Exposures of bystanders are likely to be orders of magnitude less, and thus pose no apparent concern.

2012: Comparison of the effects of e-cigarette vapor and cigarette smoke on indoor air quality

Comparisons of pollutant concentrations were made between e-cigarette vapor and tobacco smoke samples. Pollutants included VOCs, carbonyls, PAHs, nicotine, TSNAs, and glycols. Non-cancer risk analysis revealed “No Significant Risk” of harm to human health for vapor samples from e-liquids. With regard to cancer risk analysis, no vapor sample from e-liquids exceeded the risk limit for either children or adults.

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Suggested studies to add to this page


2022: Association of tobacco product use with chronic obstructive pulmonary disease (COPD) prevalence and incidence in Waves 1 through 5 (2013–2019) of the Population Assessment of Tobacco and Health (PATH) Study

More Information

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