Vaping involves heating a liquid in electronic cigarettes (e-cigarettes) to produce an aerosol for inhalation. This aerosol typically contains nicotine, flavorings, and humectants like propylene glycol and vegetable glycerin. The question of whether this practice causes lung cancer is a serious public health concern, given the rapid rise in e-cigarette use. Because lung cancer often takes decades to develop, the long-term epidemiological evidence necessary for a definitive answer is still emerging.
Current Limitations in Assessing Long-Term Cancer Risk
Determining the likelihood of lung cancer from vaping is challenging because cancer development has a long latency period, often spanning 20 years or more. E-cigarettes have only been widely available for about a decade and a half, meaning long-term population data for exclusive, lifetime vapers does not exist yet. Current longitudinal studies have only a few years of follow-up, which is insufficient to capture cancer incidence.
Another significant obstacle is the prevalence of “dual users,” individuals who use both e-cigarettes and traditional combustible cigarettes. Isolating the specific risk posed by vaping alone is difficult when a user has a history of smoking, which is already the leading cause of lung cancer. Researchers must rely on molecular and cellular studies and animal studies, but these models have limitations in predicting long-term human health outcomes.
Some short-term human studies have examined biomarkers of exposure and found that exclusive vapers who were never smokers showed no significant increased risk of incident lung cancer. However, this finding is based on limited observation periods and cannot rule out future risk. Conversely, other studies show that e-cigarette exposure is associated with biomarkers reflecting cancer risk, such as increased oxidative stress, cellular apoptosis, and DNA damage, particularly after acute exposure. While these cellular changes are precursors to cancer, they do not confirm that a tumor will form, highlighting the gap between laboratory evidence and real-world clinical outcomes.
Carcinogenic Compounds Found in Vaping Aerosol
Despite the lack of long-term human data, the vaping aerosol contains several chemicals that are known or suspected carcinogens. The process of heating the e-liquid, particularly at higher temperatures, can cause the base ingredients—propylene glycol and glycerin—to decompose into carbonyl compounds. Formaldehyde and acetaldehyde are two such compounds that are classified as known human carcinogens.
The aerosol also contains tobacco-specific nitrosamines (TSNAs), potent carcinogens found in tobacco products. While TSNA levels in e-cigarette aerosol are significantly lower—up to 98% less—than in traditional cigarette smoke, they are still present, often as impurities in the nicotine. Heavy metals such as lead, nickel, and cadmium can also leach into the e-liquid from the heating coils and other metallic components.
The presence of these substances is significant because they are known to cause DNA damage and cellular mutation, the underlying mechanism for cancer development. Heavy metals and certain volatile organic compounds can induce oxidative stress, leading to cell damage. Researchers have detected more than 500 chemicals in some tested vaping cartridges, many of which are categorized as carcinogens, suggesting a complex mixture of potential long-term harm.
Immediate and Non-Cancerous Lung Injury
While the question of lung cancer remains a long-term concern, vaping can cause immediate and acute harm to the lungs. E-cigarette or Vaping Product Use-Associated Lung Injury (EVALI) is a severe inflammatory condition that emerged as an outbreak in 2019. The vast majority of EVALI cases were strongly linked to the use of tetrahydrocannabinol (THC)-containing vaping products that included Vitamin E acetate as an additive.
Vitamin E acetate is safe to consume orally or apply topically, but when inhaled into the deep lung tissues, it acts like a thick oil, causing significant damage. EVALI symptoms include shortness of breath, cough, chest pain, and gastrointestinal issues, often requiring hospitalization. Though cases have declined since the additive was identified and removed from many illicit products, the event demonstrated the immediate dangers of unregulated e-liquid ingredients.
Another non-cancerous risk involves flavorings like diacetyl, which can cause bronchiolitis obliterans, commonly known as “popcorn lung.” This condition leads to permanent scarring and narrowing of the small airways in the lungs. Even the base humectants, propylene glycol and vegetable glycerin, can cause irritation and inflammation in the lung tissue, potentially leading to chronic issues separate from cancer.
Contextualizing Vaping Risk Against Combustible Cigarettes
To understand the risk from vaping, it is helpful to place it within the context of the known dangers of smoking traditional combustible cigarettes. Cigarettes involve the burning of tobacco, a process that creates thousands of chemicals, including over 70 known carcinogens. Studies consistently show that exclusive e-cigarette use results in significantly lower exposure to many tobacco-related toxicants and carcinogens compared to smoking.
Biomarkers of exposure to many volatile organic compounds (VOCs) and tobacco-specific nitrosamines (TSNAs) are reduced by 10% to 98% in exclusive vapers compared to exclusive smokers. This reduction in toxicant exposure supports the view that e-cigarettes are less harmful than smoking for individuals who switch completely. However, this does not mean vaping is safe, as exclusive vapers still show higher concentrations of some toxic metals like cadmium and lead compared to non-users.
The hierarchy of risk is clear: not using any nicotine or tobacco product carries the lowest risk. For current smokers, switching entirely to e-cigarettes is generally considered a move toward reduced harm due to the lower level of toxicant exposure. However, using both products concurrently, known as dual use, often results in the highest overall toxicant exposure. The key message is that while vaping appears less harmful than smoking, it introduces new chemicals and risks, and its long-term impact on lung cancer remains an open scientific question.