Applied Evidence

E-cigarettes: How “safe” are they?

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Without tobacco, tar, ash, or carbon monoxide, e-cigarettes are marketed as “healthier” alternatives to cigarettes. But they are not without risk.


From The Journal of Family Practice | 2016;65(6):380-385.



› Inform patients that e-cigarette vapors contain toxic substances, including the heavy metals lead, cadmium, and nickel. A
› Educate all patients—particularly young people and those who are pregnant or lactating—about the potential health risks of e-cigarettes. B

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series

Electronic cigarettes (e-cigarettes) have become increasingly popular over the last decade. Although they are perceived by many to be safer than traditional cigarettes, many of the devices still contain nicotine, and inhaling their vapors exposes users to toxic substances, including lead, cadmium, and nickel—heavy metals that are associated with significant health problems.1 (For more on how e-cigarettes work, see “Cigarettes vs e-cigarettes: How does the experience (and cost) compare?”)

In addition, many people use e-cigarettes as a means to stop smoking, but few who do so achieve abstinence.2,3 They frequently end up utilizing both, increasing their health risks by exposing themselves to the dangers of 2 products instead of one.1

Further complicating the issue is that the manufacture and distribution of e-cigarettes has not been well regulated. Without regulation, there is no way to know with certainty how much nicotine the devices contain and what else is in them.

Things, however, are changing. The Food and Drug Administration (FDA) recently announced that e-cigarettes and other tobacco products like cigars and hookahs will now be regulated in the same way the government regulates tobacco cigarettes and smokeless tobacco.4 The rule will not take effect immediately because companies requested time to comply, but once it is enacted, packaging will be required to list what the products contain, among other changes.

Keeping up on the latest information on e-cigarettes is now—and will continue to be—important as family physicians are increasingly asked about them. What follows is a review of what we know about their potential risks.


E-cigarettes: How “safe” are they image © 2016 iStock

A nicotine system developed by a pharmacist

E-cigarettes, or electronic nicotine delivery systems, were patented in 2003 by a Chinese pharmacist.5 Since their introduction to North America and Europe in 2007, the devices have become known by over 400 different brand names.6 Consumption among adults doubled by 2012, and by 2014, about 4% of US adults used e-cigarettes every day or some days.7 Many of them are dual users of tobacco and electronic cigarettes. In fact, Jenkins and colleagues reports in this issue of JFP (see "E-cigarettes: Who's using them and why?") that over half of cigarette smokers (52%) in their study use e-cigarettes, usually to either lower their cigarette consumption or aid in smoking cessation. (Throughout this article, we will use “cigarettes” and “smoking” to refer to the use of traditional tobacco cigarettes.)

In addition to concern over an increase in use among the general population, there is significant concern about the increase in e-cigarette use among US middle and high school students.1,8,9 In 2015, e-cigarettes were the most commonly used smoking product among middle and high school students, with 620,000 middle school students and nearly 2.4 million high school students using the battery-powered devices in the past 30 days.10

Many factors have contributed to the growing popularity of e-cigarettes.

  • Perceived safety. With tobacco’s dangers so thoroughly documented, many advertising campaigns tout e-cigarettes as less dangerous than conventional cigarettes in terms of their ability to cause cardiac and lung diseases and low birth weights. This is largely because e-cigarettes do not produce the combustion products of tar, ash, or carbon monoxide. In addition, many consumers are mistakenly less fearful about the nicotine added to many e-cigarettes.
  • Expectation that it helps smokers quit. Many smokers view e-cigarettes as an aid to smoking cessation.6 In fact, testimonials of efficacy in tobacco cessation abound in promotional materials and on the Web, and e-cigarettes are recommended by some physicians as a means to quit or lessen smoking of tobacco cigarettes.11
  • Wide availability and opportunities for use. The use of electronic nicotine delivery devices is sometimes permitted in places where smoking of conventional cigarettes is banned, although rules vary widely in different parts of the country. In addition, e-cigarettes are readily available for purchase on the Internet without age verification.
  • Extensive advertising. There are increasing concerns that advertising campaigns unduly target adolescents, young adults, and women.12-155 In addition to advertising, the media and social influences play significant roles in young people’s experimentation with “vaping,” the term for inhaling electronic cigarette aerosols.14,15
  • Regulation, legislation remain controversial. Currently, e-cigarettes are not required to be tested before marketing,16 but that may change with the FDA’s new regulations. The British National Public Health body, Public Health England, has documented public health benefits of e-cigarettes when used as a way to quit smoking, and provides evidence that the devices are less dangerous than traditional cigarettes.17 But this issue and public policy are the subject of ongoing debate. In 2015, the United Kingdom made it illegal to sell e-cigarettes or e-liquids to people younger than 18 years of age and urged child-proof packaging.

What’s “in” an e-cigarette—and are the ingredients toxic?

Because e-cigarettes are relatively new to the global marketplace, little research exists regarding the long-term effects and safety of their use, especially among habitual users.

Vapor/refills. E-liquids may contain a variety of substances because they have been largely unregulated, but they generally include some combination of nicotine, propylene glycol, glycerin, and flavorings. In fact, up to 7000 flavors are available,6 including such kid-friendly flavors as chocolate, cherry crush, and bubble gum.

Since many individuals continue to use traditional and electronic cigarettes, they end up in double jeopardy of toxicity through exposure to the dangers of both.

When the refills do contain nicotine, users generally derive less of the substance from the electronic devices than they do from a conventional cigarette. Researchers found that individual puffs from an e-cigarette contained 0 to 35 µg nicotine per puff.1,18 Assuming an amount at the high end of the spectrum (30 µg nicotine), it would take about 30 puffs of an e-cigarette to derive the same amount of nicotine (1 mg) typically delivered by a conventional cigarette.

The chemical make-up of the vapor and the biologic effects on animal models have been investigated using 42 different liquid refills.19,20 All contained potentially harmful compounds, but the levels were within exposure limits authorized by the FDA. These potentially dangerous chemicals include the known toxins formaldehyde, acrolein, and hydrocarbons.20

An inflammatory response to the inhalation of the vapors was demonstrated in mouse lungs; exposure to e-cigarette aerosols reduced lung glutathione—an important enzyme in maintaining oxidation-reduction balance—to a degree similar to that of cigarette smoke exposure.20 Less of the enzyme facilitates increased pulmonary inflammation.

In addition, human lung cells release pro-inflammatory cytokines when exposed to e-cigarette aerosols.20 Other health risks include:

Harm to indoor air quality/secondhand exposure. Even though e-cigarettes do not emit smoke, bystanders are exposed to the aerosol or vapor exhaled by the user, and researchers have found varying levels of such substances as formaldehyde, acetaldehyde, isoprene, acetic acid, acetone, propanol, propylene glycol, and nicotine in the air. However, it is unclear at this time whether the ultra-fine particles in the e-cigarette vapor have health effects commensurate with the emissions of conventional cigarettes.1,21,22

Cartridge refill ingestion by children. Accidental nicotine poisonings, particularly among children drawn to the colors, flavors, and scents of the e-liquids, have been problematic. In 2014, for example, over 3500 exposures occurred and more than half of those were in children younger than 6 years of age. (Exposure is defined as contact with the substance in some way including ingestion, inhalation, absorption by the skin/eyes, etc; not all exposures are poisonings or overdoses).23 Although incidence has tapered off somewhat, the American Association of Poison Control Centers reports that there were 623 exposures across all age groups between January 1, 2016 and April 30, 2016.23

Many people use e-cigarettes as a means to stop smoking, but few who do so achieve abstinence.

Environmental impact of discarded e-cigarettes. Discarded e-cigarettes filling our landfills is a new and emerging public health concern. Their batteries, as do all batteries, pollute the land and water and have the potential to leach lead into the environment.24 Similarly, incompletely used liquid cartridges and refills may contain nicotine and heavy metals, which add to these risks.24

Explosions. Fires and explosions have been documented with e-cigarette use, mostly due to malfunctioning lithium-ion batteries.25 Thermal injuries to the face and hands can be significant.

Heavy metals. The presence of lead, cadmium, and nickel in inhaled e-cigarette vapor is another area of significant concern, particularly for younger people who might have long-term exposure.1 All 3 heavy metals are known to be toxic to humans, and safe levels of inhalation have not been established.

Inhalation and/or ingestion of lead, in particular, can cause severe neurologic damage, especially to the developing brains of children.26 Lead also results in hematologic dysfunction. Because of the risks associated with inhalation of this heavy metal, the substance was removed from gasoline years ago.

Inhaled cadmium induces kidney, liver, bone, and respiratory tract pathology27 and can cause organ failure, hypertension, anemias, fractures, osteoporosis, and/or osteomalacia.28 And inhaling nickel produces an inflammatory pulmonary reaction.29

Pregnancy/lactation. Since no clear evidence exists on the safety of e-cigarette use during pregnancy, women should avoid exposure to these vapors during the entire perinatal period. Similarly, the effects of e-cigarettes on infants who are breastfeeding are not established. Pregnant and breastfeeding women should not replace cigarettes with e-cigarettes.30,31 For pregnant women who smoke, the US Preventive Services Task Force (USPSTF) advises using only behavioral methods to stop cigarette use.32 And until more information becomes available, exposing infants and young children to e-cigarette vapor during breastfeeding is not recommended.

On the flip side, without tobacco, tar, ash, or carbon monoxide, e-cigarettes may have some advantages when compared with the use of traditional cigarettes, but that has not been substantiated.

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