184.108.40.206 Respiratory infections and defences of the respiratory tract
The continual exposure of the airways to chemicals from e-cigarettes leads to subclinical effects on the respiratory system (see Section 18.6.5) and may cause long-term inflammatory changes that have the potential to increase the risk of infections. A number of laboratory and animal studies show that e-cigarette emissions affect the immune protection of the respiratory tract. However, there is little evidence to date of an increase in the risk of respiratory infections for people who use e-cigarettes. Longer-term studies are necessary to test the risk of respiratory infections in people who use e-cigarettes over a sustained period.
With one of the largest surface areas of the body that is exposed to the environment, the lung membrane is an important barrier to pathogens such as viruses, fungi and bacteria. Protecting the airways and lungs from infection are innate defences and adaptive immune responses. Innate defences include 1) the mucociliary clearance system (see Section 220.127.116.11), 2) innate immune cells such as macrophages and neutrophils that directly fight against bacteria, and 3) components of alveolar fluid that have anti-microbial and anti-viral properties.1 Laboratory and animal experiments investigating exposure to e-cigarette emissions have detected changes to the immune defences of the airways that may increase the risk of respiratory infections.2 , 3
Exposure of human respiratory tract cells to e-cigarette emissions leads to impairment of the functions of innate immune cells— the first line of immune defence against pathogens.2-5 Experiments characterising immune cells in the sputum (phlegm) of e-cigarette users showed similar changes.6 Flavoured e-liquids containing cinnamaldehydes exert a dose-dependent suppression of the activity of innate immune cells7 and mucosal ciliary clearance, which protects the lungs from pathogens.8 Cells from the human respiratory tract were more likely to become infected with human rhinovirus (a cause of the common cold) if exposed to e-cigarette emissions in laboratory experiments.9
Animal experiments have demonstrated that exposure to e-cigarette emissions damages the immune system and increases the risk of infection. Exposure to e-cigarette emissions or chemicals found in these emissions disrupted the normal immune system function10 and worsened respiratory bacterial infections in mouse experiments.3 An increased adherence of bacteria to respiratory lining cells has been shown in laboratory experiments that may be contributing to increased bacterial infections in these pre-clinical experiments.3 , 5 , 11 Mouse experiments have also shown an increase in lung inflammation with bacterial infection and increased weight loss and mortality from influenza after exposure to e-cigarette emissions.3 , 12 , 13
Exposure to e-cigarette emissions may also affect respiratory pathogens themselves. Laboratory experiments have shown that e-cigarette emissions increased the virulence (harmfulness) and inflammatory potential of bacteria that commonly infect the lungs.14
18.104.22.168 Risk of COVID-19 infection and disease severity
COVID-19 disease is caused by infection with the SARS-CoV-2 virus. See Section 22.214.171.124 for more details about the COVID-19 pandemic. Many large studies indicate that cigarette smoking is associated with a lower risk of COVID-19 diagnosis but a higher risk of more severe disease in those who are diagnosed (see Section 126.96.36.199). However, there are considerably fewer studies examining the risk of COVID-19 diagnosis and disease severity associated with e-cigarette use. Most of these studies indicate no association between e-cigarette use and infection with the SARS-CoV-2 virus, with few addressing the severity of disease.
Six studies failed to detect any change in the risk of contracting COVID-19 disease for people who used e-cigarettes compared to non-users.15-20 One early study found a five-fold increased risk of COVID-19 diagnosis for people who had ever used e-cigarettes, but not for current users. But the design and statistical analysis of this study have been criticised.21 , 22 Larger studies with longitudinal measures are necessary to address this question more comprehensively.
A case-control study of COVID-19 patients in the US found that e-cigarette users had a higher risk of chest pain, chills, muscle aches, headaches, loss of smell/taste, nausea/vomiting, abdominal pain, diarrhoea and non-severe light-headedness.23 However, three other studies16 , 17 , 24 did not find similar increases in COVID-19 disease severity and one study showed unclear results.25 One study of dual use (e-cigarettes and combustible cigarettes) and poly-use (e-cigarettes, combustible cigarettes and cigars) found a higher risk of severe outcomes from COVID-19 disease for dual and poly-users than people who only used e-cigarettes.26
188.8.131.52 Risk of other infectious diseases
Laboratory experiments with gut lining cells indicate that chronic e-cigarette use could disrupt the lining of the gut. These experiments used non-nicotine e-cigarette emissions, showing the effects of the other chemicals present. The study showed that repetitive, but not acute, exposure to e-cigarette aerosols disrupted the cellular barrier of the gut, increased the susceptibility of the gut lining to bacterial infections (for laboratory-grown cells) and triggered gut inflammation.27 There is, however, a lack of studies addressing infection of the gastrointestinal tract in people who use e-cigarettes.
Infections of the oral cavity are discussed in Section 184.108.40.206.
Relevant news and research
For recent news items and research on this topic, click here. ( Last updated January 2023)
1. Martin TR and Frevert CW. Innate immunity in the lungs. Proceedings of the American Thoracic Society, 2005; 2(5):403-11. Available from: https://pubmed.ncbi.nlm.nih.gov/16322590/
2. Miyashita L and Foley G. E-cigarettes and respiratory health: the latest evidence. The Journal of physiology, 2020. Available from: https://www.ncbi.nlm.nih.gov/pubmed/32495367
3. Kalininskiy A, Kittel J, Nacca NE, Misra RS, Croft DP, et al. E-cigarette exposures, respiratory tract infections, and impaired innate immunity: a narrative review. Pediatric Medicine, 2021; 4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/34095814
4. Corriden R, Moshensky A, Bojanowski CM, Meier A, Chien J, et al. E-cigarette use increases susceptibility to bacterial infection by impairment of human neutrophil chemotaxis, phagocytosis and NET formation. American Journal of Physiology-Cell Physiology, 2019. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31664858
5. Hwang JH, Lyes M, Sladewski K, Enany S, McEachern E, et al. Electronic cigarette inhalation alters innate immunity and airway cytokines while increasing the virulence of colonizing bacteria. Journal of Molecular Medicine, 2016; 94(6):667-79. Available from: https://pubmed.ncbi.nlm.nih.gov/26804311/
6. Reidel B, Radicioni G, Clapp P, Ford AA, Abdelwahab S, et al. E-cigarette use causes a unique innate immune response in the lung involving increased neutrophilic activation and altered mucin secretion. American Journal of Respiratory and Critical Care Medicine, 2017. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29053025
7. Clapp PW, Pawlak EA, Lackey JT, Keating JE, Reeber SL, et al. Flavored e-cigarette liquids and cinnamaldehyde impair respiratory innate immune cell function. American Journal of Physiology - Lung Cellular and Molecular Physiology, 2017. Available from: http://www.ncbi.nlm.nih.gov/pubmed/28495856
8. Clapp PW, Lavrich KS, van Heusden CA, Lazarowski ER, Carson JL, et al. Cinnamaldehyde in flavored e-cigarette liquids temporarily suppresses bronchial epithelial cell ciliary motility by dysregulation of mitochondrial function. American Journal of Physiology - Lung Cellular and Molecular Physiology, 2019; 316(3):L470-l86. Available from: https://pubmed.ncbi.nlm.nih.gov/30604630/
9. Wu Q, Jiang D, Minor M, and Chu HW. Electronic cigarette liquid increases inflammation and virus infection in primary human airway epithelial cells. PLoS One, 2014; 9(9):e108342. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25244293
10. Szafran BN, Pinkston R, Perveen Z, Ross MK, Morgan T, et al. Electronic-cigarette vehicles and flavoring affect lung function and immune responses in a murine model. International Journal of Molecular Sciences, 2020; 21(17). Available from: https://www.ncbi.nlm.nih.gov/pubmed/32825651
11. Miyashita L, Suri R, Dearing E, Mudway I, Dove Rosamund E, et al. E-cigarette vapour enhances pneumococcal adherence to airway epithelial cells. European Respiratory Journal, 2018; 51(2). Available from: http://erj.ersjournals.com/content/erj/51/2/1701592.full.pdf
12. Madison MC, Landers CT, Gu B-H, Chang C-Y, Tung H-Y, et al. Electronic cigarettes disrupt lung lipid homeostasis and innate immunity independent of nicotine. Journal of Clinical Investigation, 2019; 129(10):4290-304. Available from: https://doi.org/10.1172/JCI128531
13. Sussan TE, Gajghate S, Thimmulappa RK, Ma J, Kim JH, et al. Exposure to electronic cigarettes impairs pulmonary anti-bacterial and anti-viral defenses in a mouse model. PLoS One, 2015; 10(2):e0116861. Available from: https://pubmed.ncbi.nlm.nih.gov/25651083/
14. Gilpin DF, McGown KA, Gallagher K, Bengoechea J, Dumigan A, et al. Electronic cigarette vapour increases virulence and inflammatory potential of respiratory pathogens. Respiratory Research, 2019; 20(1):267. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31847850
15. Kale D, Herbec A, Perski O, Jackson SE, Brown J, et al. Associations between vaping and Covid-19: Cross-sectional findings from the HEBECO study. Drug and Alcohol Dependence, 2021; 221:108590. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33631546
16. Burnett-Hartman AN, Goldberg Scott S, Powers JD, Clennin MN, Lyons JA, et al. The association of electronic cigarette use with SARS-CoV-2 infection and COVID-19 disease severity. Tobacco Use Insights, 2022; 15:1179173x221096638. Available from: https://pubmed.ncbi.nlm.nih.gov/35492220/
17. Chen DT and Kyriakos CN. Cigarette and e-cigarettes dual users, exclusive users and COVID-19: Findings from four UK birth cohort studies. International Journal of Environmental Research and Public Health, 2021; 18(8). Available from: https://www.ncbi.nlm.nih.gov/pubmed/33918098
18. Jose T, Croghan IT, Hays JT, Schroeder DR, and Warner DO. Electronic cigarette use is not associated with COVID-19 diagnosis. J Prim Care Community Health, 2021; 12:21501327211024391. Available from: https://www.ncbi.nlm.nih.gov/pubmed/34109870
19. Garcia Colato E, Rosenberg M, Ludema C, Kianersi S, Luetke M, et al. Does cigarette or E-cigarette use increase the risk for SARS-CoV-2 seroconversion among Midwestern college students? Journal of American College Health, 2022:1-7. Available from: https://pubmed.ncbi.nlm.nih.gov/35728069/
20. Young-Wolff KC, Slama NE, Alexeeff SE, Prochaska JJ, Fogelberg R, et al. Electronic cigarette use and risk of COVID-19 among young adults without a history of cigarette smoking. Preventive Medicine, 2022; 162:107151. Available from: https://pubmed.ncbi.nlm.nih.gov/35809821/
21. Brown N. PubPeer comments on Association Between Youth Smoking, Electronic Cigarette Use, and COVID-19. PubPeer 2022. Available from: https://pubpeer.com/publications/CEB008BBD48F89272321EB50092793.
22. Farsalinos K and Niaura R. E-cigarette use and COVID-19: questioning data reliability. The Journal of Adolescent Health, 2021; 68(1):213. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33349352
23. McFadden DD, Bornstein SL, Vassallo R, Salonen BR, Bhuiyan MN, et al. Symptoms COVID 19 positive vapers compared to COVID 19 positive non-vapers. Journal of Primary Care & Community Health, 2022; 13:21501319211062672. Available from: https://www.ncbi.nlm.nih.gov/pubmed/34986700
24. Axelsson GT, Eythorsson ES, Hardardottir H, Gudmundsson G, and Hansdottir S. [The impact of lung diseases, smoking and e-cigarette use on the severity of COVID-19 illness at diagnosis]. Laeknabladid, 2020; 106(12):574-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33252049
25. Gao M, Aveyard P, Lindson N, Hartmann-Boyce J, Watkinson P, et al. Association between smoking, e-cigarette use and severe COVID-19: a cohort study. International Journal of Epidemiology, 2022. Available from: https://pubmed.ncbi.nlm.nih.gov/35179598/
26. Merianos AL, Russell AM, Mahabee-Gittens EM, Barry AE, Yang M, et al. Assessment of exclusive, dual, and polytobacco e-cigarette use and COVID-19 outcomes among college students. American Journal of Health Promotion, 2021:8901171211055904. Available from: https://www.ncbi.nlm.nih.gov/pubmed/34865520
27. Sharma A, Lee J, Fonseca AG, Moshensky A, Kothari T, et al. E-cigarettes compromise the gut barrier and trigger inflammation. iScience, 2021; 24(2):102035. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33537654