Electronic cigarettes, or vapes, were introduced in the 2000s as a tool to help people give up tobacco smoking — a dangerous habit that kills half of lifelong users¹. Backed by widespread public-health messages that vaping is 95% safer (see go.nature.com/4ixya3r) than cigarette smoking, manufacturers and some physicians have been keen to extol the virtues of these electronic systems for delivering nicotine to established smokers who are addicted to the substance.

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Yet, the safety of e-cigarettes is not well established — even the evidence on which the 95% claim was based is hard to pin down. The health issues associated with e-cigarettes started to emerge a decade ago. As use of vapes has become more widespread, the evidence has become irrefutable. Some of the adverse effects are extremely concerning.

In particular, it has become clear that these products represent an enticing gateway to nicotine addiction for non-cigarette smokers — including children.

A systematic review published in August (for which we are co-authors) identified a range of health consequences for children and young people who vape². The extent of the likely harmful effects is wider than anticipated, and increasingly evident in the children we see in hospital practice.

Here, we outline the risks, and call for governments to act to legislate as necessary and ensure these laws are effectively enforced.

Medical tools

By design, e-cigarettes are highly efficient at delivering nicotine, at levels that are comparable with or higher than typical tobacco cigarettes³. Their efficiency probably explains their effectiveness as a quitting aid for some smokers. A meta-analysis has shown that they are more effective than other nicotine-replacement therapies as a route to smoking cessation⁴. But they are not without risk.

Nicotine is a highly addictive substance that is known, from decades of studies of smokers, to impair fetal and adolescent brain development^5,6. Even low-level, intermittent use can quickly lead to symptoms of nicotine dependence⁷. These effects are particularly pronounced in adolescence, with some young users reporting symptoms of dependence, including cravings and withdrawal from occasional exposure⁸.

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E-cigarettes have been shown to contain harmful substances, including heavy metals, such as lead; toxic carbonyls; nanoparticles; and unregulated substances, such as synthetic cannabinoids⁹. The longer-term health concerns are yet to emerge, but these substances are known to be pro-inflammatory, immunosuppressive, carcinogenic and highly addictive in their own right.

The continued increase in vape use since their development has coincided with the rediscovery of nicotine salts. In the 1970s, manufacturers refined their processing techniques to strip away the protons and organic acids from naturally occurring nicotine salts. The resulting, unbound (freebase) nicotine is uncharged and attracted to fat. These chemical properties result in quicker absorption and transit to the brain, and a more intense sensory experience or nicotine ‘hit’¹⁰. Freebased cigarettes rapidly came to dominate the market.

In 2017, vape manufacturers found that the salt-based nicotine tasted smoother and sweeter. They added these salts to vapes to improve the sensory experience. The effect is particularly strong for individuals who have never smoked and are unaccustomed to inhaling freebase nicotine¹¹.

Studies have shown that some nicotine-salt products can produce higher and more rapid peaks in blood nicotine levels¹². Vape manufacturers have also quickly seized on the opportunity to make these products attractive to younger users with sweet and fruity flavours and colourful packaging.

Health risks of vaping in children

Early studies on the possible risks of vaping for all age groups have concentrated on the acute effects, such as immediate reductions in lung function or emergence of respiratory symptoms¹³. But these are likely to be the tip of the iceberg with respect to overall harm. In our systematic review, we identified a worrying range of possible risks from vaping at a young age.

As respiratory paediatricians, we were not particularly surprised to see that vaping in childhood was consistently associated with a cough, chest discomfort, a wheeze and a wet cough. The direct effects of inhaling hot gases and chemicals might also account for the observed increase in oral and dental disease, such as gingival inflammation, ulcers and dry mouth, as well as eye symptoms such as itching, redness, dryness, blurriness and pain in the studies we looked at. An increase in allergic conditions such as atopic dermatitis and allergic rhinitis was also reported.

We expected nicotine, a potent stimulant of the central nervous system, to have effects beyond the respiratory system. Yet, we were surprised by the extent to which vaping in young people is associated with poorer mental health. Depression, panic disorder, anhedonia and suicidal ideation were all more commonly reported in individuals who vape. That young e-cigarette users were almost twice as likely as non-users to have suicidal thoughts or plans, or attempts at suicide, is concerning.

It was also worrying to see that there are likely to be harmful effects to unborn babies. Our review highlighted higher rates of preterm birth, small-for-gestational-age birth weight, abnormal reflexes and motor immaturity in infants born to mothers who vaped.

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The most alarming finding for us was the strong evidence that vaping in children and young people who have never smoked predicts and increases the likelihood of subsequent conventional cigarette smoking. E-cigarette users were typically 2–12 times more likely than non-users to subsequently start smoking.

This return to a deadly practice is especially galling given the healthier choices that children born after the millennium were beginning to make. The dramatic decline in alcohol consumption, drug use, teenage pregnancy, criminality and smoking in people aged 16–24 years in the United Kingdom led to them to be dubbed generation sensible by the media in 2018.

Although vaping offers a helpful adjunct to smoking-cessation programmes for adults, its unsubstantiated and simplistic promotion as a safe alternative to cigarettes has led to unintended consequences for non-smoking children and young people.

Increased vaping among children and young people is a global phenomenon spanning continents and markedly different cultures¹⁴. The time course of vaping varies by country.