This is not yet known for certain, because vaping is new and there are no long-term studies in people [1, 7]. E-cigarette vapour contains toxic substances and some cancer-causing substances, but at much lower levels than cigarette smoke; so vaping is probably far less risky than smoking, but it is not harmless [1, 2]. If you do not smoke, do not start vaping; if you smoke, the best step is to quit completely, and smoking and vaping at the same time does not lower your exposure to carcinogens [3, 7].
Key points
- There is no definite answer yet: no study in people has shown whether or not vaping causes cancer; long-term studies do not exist yet [1].
- Vapour is not harmless: it contains toxic substances, metals and some carcinogens such as formaldehyde [1, 7].
- But far less than cigarette smoke: levels of these substances in e-cigarette vapour were 9 to 450 times lower than in cigarette smoke [2].
- If you do not smoke, do not start, especially young people; vaping makes them more likely to take up smoking [1, 7].
- For quitting smoking: the long-term safety of e-cigarettes is not yet known [5]; use proven quitting methods, with your doctor’s help.
- Smoking and vaping? Using both does not lower exposure to carcinogens; the benefit comes only from stopping smoking completely [3, 4].
What is in e-cigarette vapour?
An e-cigarette heats a liquid and turns it into a vapour (aerosol); the liquid usually contains nicotine, flavourings and other substances, but no tobacco [7]. Because nothing is burned, most of the toxic substances in cigarette smoke are absent or present at much lower levels [1]. Even so, e-cigarette vapour is not harmless:
- Besides nicotine, most e-cigarettes contain many potentially toxic substances, and their amounts depend on the device, the liquid and how it is used [1].
- Some of these substances, such as formaldehyde and acrolein, can damage DNA (the genetic material of cells); so, scientifically, long-term use could plausibly raise the risk of cancer [1].
- E-cigarette vapour contains metals, which can come from the heating coil of the device or from the liquid itself [1].
- Nicotine is highly addictive and harms brain development in children and teenagers [7].
Vaping and cancer: what we know and what we do not know
| Topic | What we know |
|---|---|
| Carcinogens in vapour | They are present, but at much lower levels than in cigarette smoke [1, 2] |
| Cancer in people | No study has yet shown whether or not vaping causes cancer [1] |
| Lungs | There is not yet enough evidence on lung disease in people; cough and wheeze are more common in teenagers who vape [1], and lung injury linked to vaping has been reported [7] |
| Mouth | There is limited evidence of damage to mouth cells in non-smokers [1] |
| Bladder | Substances linked to bladder cancer have been found in users' urine; the long-term consequences are unknown [6] |
| Young people | Vaping makes young people more likely to take up smoking [1, 7] |
The World Health Organization says it is still too early to give a clear answer on the long-term effects of vaping, but we know that e-cigarettes produce substances, some of which cause cancer [7].
Vaping compared with smoking
In laboratory tests, levels of toxic and cancer-causing substances in the vapour of 12 e-cigarette brands were 9 to 450 times lower than in cigarette smoke [2]. The same was seen in users' bodies: former smokers who had used only e-cigarettes for a long time had far lower levels of carcinogens in their urine and saliva than smokers [3].
But "less" does not mean "harmless". In a large American study, levels of toxic substances in the bodies of people who only vaped were lower than in smokers, but higher than in people who used neither [4]. A group of American scientists who reviewed all the evidence concluded that e-cigarettes are probably far less harmful than cigarettes, but that their true level of risk is not yet known [1]. The World Health Organization stresses that both cigarettes and e-cigarettes carry health risks and that the safest choice is to use neither [7].
Smoking and vaping together: the worst option
Many smokers start vaping but do not give up cigarettes. No benefit has been seen in this situation:
- People who both smoked and vaped had as many carcinogens in their bodies as smokers [3].
- In the large American study, levels of some toxic substances in these people were even higher than in those who only smoked; the more cigarettes, the more toxic substances [4].
- The World Health Organization says that using both is at least as dangerous as smoking and probably more dangerous [7].
Can vaping help you quit smoking?
Some studies have looked at nicotine e-cigarettes as a way to help people stop smoking; no serious short-term harm was seen, but their long-term safety is still not clear [5].
The US Preventive Services Task Force advises smokers to use proven methods, counselling together with stop-smoking medicines [8], and the World Health Organization also recommends proven ways to quit [7]. See these methods here: How much does quitting smoking lower cancer risk?
What should I do? One important step: neither cigarettes nor e-cigarettes; if you smoke, quit completely
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If you use neither, do not start
The safest choice is to neither smoke nor vape [7]. Hookah (waterpipe) is not harmless either; see: Does hookah cause cancer?
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If you smoke, get help to quit
Counselling together with stop-smoking medicines are the proven methods; ask your doctor for help [8]. See: How much does quitting smoking lower cancer risk?
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If you are using e-cigarettes to quit, stop smoking completely
Frequently asked questions
Does vaping cause lung cancer?
This is not yet known. No study in people has shown whether or not vaping causes lung cancer, because this cancer usually appears many years later and vaping is new [1, 7]. E-cigarette vapour contains substances that can damage DNA [1]. If you have a long-lasting cough or blood in your phlegm, see a doctor; see: Symptoms of lung cancer.
Are nicotine-free e-cigarettes safe?
Is second-hand vapour harmful to people nearby?
What was the vaping-related lung injury?
In 2019 and 2020 in the United States, nearly 2,800 people developed lung injury linked to vaping and 68 died [7]. A substance called vitamin E acetate, added to some liquids containing THC (the active substance in cannabis), is thought to have played an important role [7]. Do not use unauthorised or tampered-with liquids and devices [7].
I quit smoking with e-cigarettes. Should I keep vaping?
Does vaping affect the bladder and the mouth?
Substances linked to bladder cancer have been found in the urine of people who vape; their long-term effect is not yet known [6]. There is also limited evidence of damage to mouth cells [1]. See: Symptoms of bladder cancer and Symptoms of mouth cancer.
Details of the evidence (for physicians)
For physicians
NASEM 2018 conclusions. Cancer: there is no available evidence whether or not e-cigarette use is associated with intermediate cancer endpoints in humans (Conclusion 10-1); limited evidence from in vivo animal studies using intermediate biomarkers, and no adequate long-term animal bioassays (10-2); limited evidence that the aerosol can be mutagenic or cause DNA damage (10-3); substantial evidence that some aerosol chemicals (formaldehyde, acrolein) cause DNA damage and mutagenesis, supporting the biological plausibility of an increased cancer risk with long-term exposure (10-4). Exposure: conclusive evidence that most products contain and emit numerous potentially toxic substances besides nicotine (5-1); substantial evidence that, under typical use, exposure to toxic substances other than nicotine is significantly lower than with cigarettes (5-3) and that the aerosol contains metals (5-4); conclusive evidence that completely substituting e-cigarettes for cigarettes reduces exposure to numerous toxicants and carcinogens (18-1); no available evidence on whether dual use changes morbidity or mortality (18-3). Lungs: no available evidence whether e-cigarettes cause respiratory disease in humans (11-1) and moderate evidence of increased cough and wheeze in adolescents (11-4); mouth: limited evidence of damage to oral tissue cells in non-smokers (12-2). Young people: substantial evidence that e-cigarette use increases the risk of ever using cigarettes among youth and young adults (16-1). The committee's summary: e-cigarettes are "likely to be far less harmful" than cigarettes, but their absolute risk cannot be determined at present [1].
Toxicants and biomarkers. Goniewicz 2014 (12 brands; carbonyls, VOCs, nitrosamines and metals): levels 9 to 450 times lower than in cigarette smoke and in many cases comparable with trace amounts from a medicinal nicotine inhaler [2]. Shahab 2017 (cross-sectional, 181 people, 36 to 37 per group): long-term (≥6 months) e-cigarette-only or NRT-only use was associated with significantly lower TSNA (including NNAL) and VOC metabolites than smoking only or dual use; the lowest NNAL with e-cigarettes only; dual use of e-cigarettes or NRT with cigarettes gave levels broadly similar to smoking only [3]. PATH (Goniewicz 2018; 5,105 adults: 247 e-cigarette only, 2,411 cigarette only, 792 dual users, 1,655 never users; 50 biomarkers): e-cigarette-only users 10 to 98% lower than cigarette-only smokers (TSNAs, PAHs, most VOCs and nicotine) and comparable for metals and 3 VOCs; never users 19 to 81% lower than e-cigarette-only users (nicotine, TSNAs, cadmium, lead and some VOCs); cigarette-only smokers 10 to 36% lower than dual users for several biomarkers, with cigarette frequency positively correlated with exposure [4]. Bladder (Bjurlin 2021, systematic review of 22 studies): 40 parent compounds, 4 metals and 63 metabolites in users' urine; several carcinogens linked to bladder cancer higher than in non-users; most studies lacked never-smoker controls [6].
Smoking cessation. Cochrane 2026 (living review, 80 trials, 29,861 participants): nicotine e-cigarettes vs NRT RR 1.61 (1.23 to 2.12; 11 studies, 4,114 participants; high certainty), about 4 additional quitters per 100 (1 to 7); similar SAEs (RD 0.01; −0.01 to 0.02); vs non-nicotine e-cigarettes 1.34 (1.05 to 1.69) and vs behavioural support or no support 1.75 (1.39 to 2.20; low certainty); only regulated nicotine e-cigarettes were tested, and illicit or THC-containing products may have different harm profiles [5]. USPSTF 2021: insufficient evidence for e-cigarettes for cessation (I statement); direct patients to interventions with proven effectiveness and established safety [8]. WHO 2024: e-cigarettes as consumer products have not been proven effective for cessation at the population level; e-cigarette use increases cigarette uptake among non-smoking youth nearly threefold; dual use is at least as dangerous as smoking; EVALI: as of 18 February 2020, 2,807 cases and 68 deaths in the United States, with vitamin E acetate in THC-containing products thought to have played a significant role [7].
In practice. Ask about e-cigarette use in the history; advise adults who switch to e-cigarettes to switch completely and avoid dual use [1, 3, 4]; for quitting, first offer counselling and approved medicines [8].
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References
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Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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