18B.5 Safety and health risks of e-cigarettes

Last updated: November 2018         

Suggested citation: Greenhalgh, EM, & Scollo, MM. InDepth 18B: Electronic cigarettes (e-cigarettes). In Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2018. Available from: http://www.tobaccoinaustralia.org.au/chapter-18-harm-reduction/indepth-18b-e-cigarettes

Due to the recency of their introduction to the market, there are no controlled studies on the safety of long-term use of e-cigarettes; however, since e-cigarettes do not generate the smoke that is produced by burning tobacco, their use is generally accepted as likely to be less harmful than smoking conventional cigarettes.1-3 Immediate short term adverse effects of exposure to e-cigarettes are usually mild and transient, and may include nausea, vomiting, mouth and airway irritation, chest pain, and palpitations.4   

E-cigarettes deliver nicotine by creating an aerosol of ultrafine particles, but due to the variability and chemical complexity of fine particles and uncertainty regarding the specific components responsible for toxicity, it is unknown whether e-cigarettes have health effects and toxicity similar to the ambient fine particles generated by conventional cigarette smoke or secondhand smoke.5, 6 This uncertainty is further confounded by the lack of regulation and manufacturing standards, leading to potentially harmful and widely varying ingredients, and significant inconsistency between the labelled content and the actual content and concentrations.7, 8 It has become apparent in Australia that some e-cigarettes which are claimed to be free of nicotine, do in fact contain the substance.9 The NSW Ministry of Health tested samples of e-liquids in 2013 and found that 70% of the samples contained high levels of nicotine.10      

A large amount of research is published each month on this topic, and several agencies in Australia and internationally now have conducted reviews of the evidence. Readers are directed to comprehensive reports published early in 2018 by the US National Academies of Science, Engineering and Medicine,11 and a report published later in 2018 by Australia’s CSIRO.12

18B5.1 Health effects of e-cigarette use during pregnancy  

While smoking during pregnancy is a well-established cause of infant illness and death, there is a lack of evidence on the effects of e-cigarette use during pregnancy on the mother or foetus.11 Nonetheless, research on tobacco and nicotine provides some understanding of potential effects. Nicotine adversely affects maternal and foetal health during pregnancy, contributing poor outcomes including preterm delivery, still birth, neonatal apnoea, and sudden infant death syndrome.13, 14 Nicotine exposure during pregnancy also has lasting adverse consequences for brain and lung development.13 Despite common perceptions among pregnant women that the products are a safer alternative to smoking, which has led to increasing use,15 there is currently no clinical knowledge of the safety of e-cigarette use in pregnancy.11 No amount of nicotine is known to be safe during pregnancy,16 and results from several animal studies suggest that maternal e-cigarette exposure during pregnancy, regardless of nicotine content, is linked to poorer health outcomes in both the mother and the offspring.12  

There is also no evidence that e-cigarettes are an effective cessation aid for pregnant women, although a large randomised controlled trial is being conducted in the UK.17 While some nicotine replacement therapy (NRT) products have been approved as safe by the TGA for use during pregnancy (see Section 7.11.5.1), there is insufficient evidence to recommend e-cigarettes for such use. The US Surgeon General noted in 2014 that ‘the evidence is already sufficient to provide appropriately cautious messages to pregnant women and women of reproductive age… about the use of nicotine-containing products such as smokeless tobacco and electronic cigarettes, and newer forms of nicotine-containing tobacco products, as alternatives to smoking.’13 The 2016 report on e-cigarette use concludes that ‘Nicotine can cross the placenta and has known effects on foetal and postnatal development. Therefore, nicotine delivered by e-cigarettes during pregnancy can result in multiple adverse consequences, including sudden infant death syndrome, and could result in altered corpus callosum, deficits in auditory processing, and obesity.’6

18B.5.2 Health effects of e-cigarette use during adolescence

There is evidence that adolescents who are exposed to nicotine may become addicted more rapidly, and at lower or more intermittent levels of consumption than adults.18-20 Evidence suggests that nicotine exposure during adolescence, a time during which the brain undergoes rapid development, may have a long-term negative impact on higher cognitive function.13, 14 The US Surgeon General’s 2014 report on the health consequences of smoking noted that ‘the evidence is already sufficient to provide appropriately cautious messages to … adolescents about the use of nicotine-containing products such as smokeless tobacco and electronic cigarettes, and newer forms of nicotine-containing tobacco products, as alternatives to smoking’.13 The 2016 report similarly concludes that ‘nicotine exposure during adolescence can cause addiction and can harm the developing adolescent brain’.6   

Aside from nicotine exposure, several studies with adolescents have found increased respiratory symptoms among e-cigarette experimenters.21 There is evidence that adolescents who use e-cigarettes experience increased cough and wheeze, and adolescents with asthma may be more likely to have an increase in respiratory symptoms and exacerbations compared with adolescents who do not use the products.11 Vaping is also associated with increased chronic bronchitic symptoms among adolescents.22 Another study reported significantly greater toxicant and carcinogen exposure in adolescent e-cigarette users compared with non-users.23

18B.5.3 E-cigarette use and possible cardiovascular disease risk  

Conflicting findings have been reported about the potential health effects of e-cigarette use on the cardiovascular system.24-28 The current body of research is limited and short-term, with a lack of high-quality studies and adequate follow-up. Some evidence suggests that e-cigarettes have sympathomimetic effects (i.e., mimicking the action of the sympathetic system) related to nicotine exposure. Limited data suggests that vascular injury may be another concern.29 The user’s heart rate and diastolic blood pressure increase after nicotine intake from e-cigarettes, and e-cigarette use may also be associated with a short-term increase in systolic blood pressure, changes in biomarkers of oxidative stress, increased endothelial dysfunction and arterial stiffness, and autonomic control.11 However, short-term changes are not necessarily associated with long-term outcomes, and there are no long-term studies to establish whether or not e-cigarette use is associated with cardiovascular disease.11, 12 Given the non-linear relationship between smoking and cardiovascular mortality—i.e., even light smoking can cause significant cardiovascular health effects—reductions in exposure to certain constituents (such as carbonyls and nicotine) through switching from tobacco to e-cigarettes may not result in proportional harm reduction.30 One study reported that compared to non-users, e-cigarette use was associated with a higher likelihood of chest pain, palpitations, coronary artery disease, and arrhythmia, though it should be noted that this study did not fully control for extent of prior use of cigarettes.31 A cross-sectional study found an association between daily e-cigarette use and increased risk of heart attacks, with a greater risk for those who also smoke, although the authors note that this type of study precludes establishing causal relationships.32

Given the lack of epidemiological data, the probability of cardiovascular disease risk needs to be assessed from data on toxicity of constituents, levels of exposure, mechanisms, and studies using experimental models. Although the cardiovascular risk is likely much less than that from smoking, e-cigarette emissions of concern for cardiovascular health may include nicotine, oxidizing chemicals, aldehydes (especially acrolein), and particulates.33 Overall, existing evidence is limited and further research is needed to establish the cardiovascular risks of using e-cigarettes long-term.

18B.5.4 E-cigarette use and possible cancer risk

The effects of long-term e-cigarette use on cancer risk are unknown. While biological samples of e-cigarette users can contain metabolites of various carcinogens and toxic compounds at levels higher than non-users, it is unknown whether they are high enough to significantly increase risk of cancer.12  Some chemicals present in e-cigarette aerosols are capable of causing DNA damage and mutagenesisi, which supports the biological plausibility that long-term exposure could increase cancer risk.11  

Small amounts of formaldehyde and acetaldehyde, both established carcinogens, have been detected in e-cigarette cartridges.34  Aerosol produced from some products has also been found to contain traces of carcinogenic nitrosamines,34 and some toxic and potentially carcinogenic metals such as cadmium, nickel, lead,34, 35 chromium, manganese, and nickel.35 A study commissioned by the US Food and Drug Administration in 2009 also detected carcinogens diethylene glycol and nitrosamines at very low levels.36 One review suggests that as propylene glycol in e-liquid is heated and aerosolised, it can be converted to propylene oxide, which is considered possibly carcinogenic to humans.37 A small study of never-smokers who had never used e-cigarettes found that one session of vaping altered activity of the tumour protein p53, which is important in preventing the development of cigarette-induced lung cancer.38  

Compared with tobacco smoke, e-cigarette emissions tend to have lower concentrations of carcinogens;34, 39 however the presence of metals in particular may disproportionately increase the cancer risk of e-cigarettes.39, 40 Some studies have suggested that newer products with higher voltage capabilities might produce the same or even higher levels of carcinogenic formaldehyde than tobacco smoke,41, 42 but their findings have been challenged.43, 44 An analysis of e-cigarette emissions concluded that highly carcinogenic emissions are avoidable, and are largely due to device settings, e-liquid formulation, and vaping behaviour, highlighting the need for consumer education on reducing risk.39  

In terms of nicotine exposure, the US Surgeon General’s most recent report concluded that there is insufficient data to conclude that nicotine causes or contributes to cancer.13 However, the International Agency for Research on Cancer Advisory Group has recommended that nicotine’s potential as a carcinogen be reassessed as a matter of high priority, because of increased population exposure to nicotine from e-cigarettes, and recent mechanistic data that ‘suggest an association with DNA damage and other pathways of carcinogenesis.’45   

18B.5.5 E-cigarette use and possible respiratory disease risk

Other than nicotine, the main ingredient in e-cigarettes is propylene glycol, which is generally considered to be safe for human consumption if swallowed. However, it has not been tested in the manner that e-cigarette use involves; that is, repeated inhalation over a long period of time.46 Frequent exposure to fine and ultrafine particles, such as tobacco smoke, air pollution, and dusts, can contribute to pulmonary and systemic inflammatory processes and increase the risk of cardiovascular and lung diseases.5 The thresholds for human toxicity of potential toxicants in e-cigarette vapour are so far unknown.5  There have been rare reports of exposure causing irritation to the upper and lower respiratory tract mucosa.47 The level of emissions of compounds such as formaldehyde, acetaldehyde, and acrolein appears to increase with the temperature and age (i.e., number of uses) of the device, and for single-coil vs. double-coil e-cigarettes.48 Exposure to metals from e-cigarette vapour, such as nickel, chromium, and titanium, may also pose particular risks to the respiratory system.37  

There is currently no definitive evidence whether or not e-cigarettes cause long-term respiratory diseases in humans.11 Limited evidence from animal and in vitro studies suggest that e-cigarette exposure has adverse effects on the respiratory system.11 E-cigarettes have been implicated in individual case reports of exogenous lipoid pneumonia, bronchiolitis, acute eosinophilic pneumonia, pneumonia with bilateral pleural effusions, and inhalation injury and suspected acute hypersensitivity pneumonitis,28 and have also been associated with asthma.49, 50  Acute use also leads to lung inflammation,37, 51, 52 which could cause or progress conditions such as COPD and oxidative damage. However, those conducting this research  point out that long-term studies are needed to better understand how such acute effects may translate to disease risk.51  

Some researchers are more inclined to conclude that harm is likely. A 2017 review concluded that there is a rapidly growing body of evidence that e-cigarette use may have significant pulmonary toxicity. Evidence suggests that e-cigarettes impact multiple regions and functions of the respiratory system, including altering airflow through the conducting airways, increasing oxidative stress, interfering with lung development, and impairing host defence against bacterial and viral pathogens.53 Further, given many e-cigarette users continue to smoke, the risks may be additive. One study found that dual users— who are exposed to toxicants from cigarette smoke, e-cigarette vapour, and nicotine from both products—reported poorer general health and greater breathing difficulty in the past month compared to those who smoked only cigarettes.31 Among ex-smokers who switch to e-cigarettes, some studies note reduced exposure to numerous respiratory toxicants, reduced asthma exacerbations, and reduced chronic obstructive pulmonary disease symptoms.11, 54

Researchers have also raised concerns regarding the potential harm of inhaled flavourings used in e-cigarettes on the respiratory system.37, 55-59 They suggest that respiratory toxins in the more than 7,000 unique flavourings might pose a threat to the respiratory health of users, particularly as the flavours have primarily been tested in regard to ingestion, rather than inhalation.56 One study found that the concentrations of some flavour chemicals in e-cigarette fluids are sufficiently high for inhalation exposure by vaping to be of toxicological concern,60 and another found that flavours (along with product type and battery output voltage) significantly affected toxicity of e-cigarette aerosol, with a strawberry-flavoured product being the most cytotoxic.59 An analysis of e-cigarette refill liquids across nine European countries found that all of the samples analysed had additives that are classified to have some level of danger/risk of hazard based on the global classification system for respiratory irritants.61 Researchers have suggested that regulatory limits should be considered for levels of some of the more worrisome chemicals as well as for total flavour chemical levels, and that ingredients should be labelled.60

18B.5.6 Other health risks 

A number of other potential health risks of e-cigarette use have been identified in recent years. One review notes that exposure to propylene glycol can cause eye irritation, while prolonged or repeated inhalation may affect the central nervous system.37  

Switching to e-cigarettes may improve periodontal disease in smokers;11 however a 2017 review concluded that e-cigarettes and/or inhaled nicotine along with various flavouring chemicals may contribute to the development of periodontal diseases.62  Limited evidence also suggests that both nicotine- and non-nicotine–containing e-cigarette aerosol can adversely affect cell viability and cause cell damage of oral tissue in non-smokers.11 Case studies have suggested that e-cigarette use interferes with, or delays, wound healing.12  

 

18B.5.7 Exposure to second-hand vapour

An additional concern regarding the use of e-cigarettes is bystanders’ exposure to second-hand vapour (as exhaled by the user), particularly if the products are used indoors. Several reviews have concluded that e-cigarettes do emit toxicants; however, these emissions are markedly lower than those from conventional cigarettes.11, 63, 64 Studies conducted in natural settings are limited and inconsistent,65 although some suggest that indoor use exposes non-users to secondhand aerosol.66 One systematic review reported that exhaled e-cigarette vapour can contain emissions at a level which affects indoor air quality, including nicotine, particulate matter, glycerine, propylene glycol, formaldehyde, acetaldehyde, polycyclic aromatic hydrocarbons (PAHs) and metals, but mostly to a lesser extent than combustible tobacco products.67 Another study concluded that short-term e-cigarette use can produce elevated fine and ultrafine particles; nicotine in the air; and accumulation of nicotine on surfaces and clothing.68

While the health impacts of exposure to second-hand vapour are likely to be less than the impact of combustible tobacco, e-cigarettes do have the capacity to produce environmental pollutants, and in sufficient quantities to potentially harm health.66, 67 Long term studies on the health effects of exposure to second-hand vapour do not yet exist; nor studies on how vapour might impact on the health of vulnerable populations, including children, pregnant women, and people with chronic lung or heart disease.67

18B.5.8 Environmental impact

Little is known so far regarding the environmental impact of e-cigarettes;ii however their manufacturing, use and disposal potentially pose serious environmental risks. In 2015, of the more than 58 million e-cigarettes and refills that were sold in US grocery and convenience stores, 19.2 million were designed for single use.69 Because of their composition—comprising both electronic components and residual nicotine and other chemicals—discarded e-cigarettes may qualify as both e-waste and biohazard waste, however there are no methods or guidelines for appropriate disposal.70 When littered or improperly discarded, broken devices can leach heavy metals and nicotine into the environment; pose choking hazards for small children; be eaten by animals; or puncture, explode, or burn. Regulations around product standards and proper disposal, recycling programs, and extended producer responsibility (whereby manufacturers establish and publicise end-of-life buyback programs) are needed to minimise the environmental health harms of e-cigarettes.70  

 

Relevant news and research

For recent news items and research on this topic, click here.(Last updated May 2019) 

 

 

i. In 2017, the Australian Competition and Consumer Commission successfully took action in the Federal court against three online e-cigarette retailers for false and misleading claims about the presence of carcinogens in e-cigarettes (see https://www.accc.gov.au/media-release/e-cigarette-companies-to-pay-penalties). 

ii. Cigarette manufacturing also has a substantial environmental impact (see section 10.15), and cigarette butt litter remains a major environmental pollutant that poisons waterways and wildlife and causes bushfires (see section 10.16). 

 

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