In recent years, the use of e-cigarettes has been increasing globally, but public awareness of the relationship between e-cigarettes and health remains limited. In 2019, an outbreak of e-cigarette or vaping product use-associated lung injury (EVALI) occurred in the United States, with more than 2,800 cases registered in less than 12 months, including 68 deaths. Similar cases have been reported in other countries such as Canada, India, and China, raising concerns about the health risks of e-cigarettes.
E-cigarette vapor contains harmful substances such as nicotine, polycyclic aromatic hydrocarbons, volatile organic compounds, ultrafine particles, heavy metals, and silicates, including carcinogens like formaldehyde. Various substances enter the body through inhalation and produce a range of biological effects, thereby posing health risks. The lungs, being the first line of defense, are particularly affected by e-cigarettes.
Current research has identified five main mechanisms by which e-cigarettes can damage lung health:
- Damage to airway epithelial cells: The airway epithelium is the body’s first line of defense against pathogens and toxic substances. Propylene glycol/vegetable glycerin in e-cigarettes can induce epithelial stress and inflammatory responses through dehydration; when inhaled in large amounts, it can also induce hyperosmotic stress, further triggering inflammatory responses and airway constriction.
- Suppression of respiratory immune function: E-cigarettes containing cinnamaldehyde suppress the immune functions of epithelial cells, neutrophils, and natural killer cells in a dose-dependent manner, leading to dysregulation of macrophage phagocytic activity and decreased bactericidal activity. Studies show that e-cigarette use is associated with an increased risk of novel coronavirus infections, and animal models have found that e-cigarette use makes airway epithelial cells more susceptible to bacterial infections and increases susceptibility to type A influenza virus.
- Increase in mucin MUC5AC: MUC5AC is a major marker of high mucus secretion. Increased MUC5AC concentrations in e-cigarette users suggest that e-cigarette use may be a risk factor for chronic lung disease.
- Lung cancer: E-cigarettes may contain nitrosamines. Mice exposed to e-cigarettes have shown a significant increase in lung tumor incidence. Further studies indicate that e-cigarettes can induce DNA damage, promoting the progression of lung cancer.
- Vitamin E acetate: Vitamin E acetate may affect the physical structure of lung surfactant, impairing its ability to maintain alveolar surface tension, thus causing respiratory dysfunction; it can also form a toxic compound, ethylene ketone, causing chemical pneumonitis in EVALI patients.
E-cigarettes have been widely used for less than 20 years, and product development has far outpaced research into their health hazards. However, current data suggest that e-cigarettes are unsafe and should not be used as a tool for quitting smoking. Non-smokers, especially adolescents, should stay away from tobacco and e-cigarettes.