Table 1
Search key words by thematic units
| Chemical composition and thermal degradation | (“electronic cigarettes” OR “vape aerosol” OR “e-liquids”) AND (“propylene glycol” OR “vegetable glycerin” OR “thermal degradation” OR “formaldehyde” OR “acrolein” OR “propylene oxide” OR “glycidol” OR “heavy metals”); |
| Pulmonary pathomorphology and immune response | (“vaping” OR “e-cigarette”) AND (“EVALI” OR “vitamin E acetate” OR “obliterative bronchiolitis” OR “popcorn lung” OR “lipoid pneumonia” OR “neutrophil dysfunction” OR “actin microfilaments”); |
| Cardiovascular and endothelial dynamics | (“electronic nicotine delivery systems” OR “vaping”) AND (“endothelial dysfunction” OR “nitric oxide” OR “ICAM-1” OR “S100A8” OR “arterial stiffness” OR “thrombogenicity”); |
| Neurodevelopment and cognitive impact | (“vaping” OR “nicotine salts”) AND (“adolescent brain” OR “prefrontal cortex” OR “hippocampus” OR “cognitive impairment” OR “executive function”); |
| Harm reduction and comparative risk | (“e-cigarettes”) AND (“harm reduction” OR “smoking cessation” OR “dual use” OR “lung cancer risk” OR “former smokers”). |
Table 2
Main toxic substances formed during e-liquid heating and their adverse effects
| Chemical compound | Parent component / Origin | Chemical formula | Primary pathophysiological impact & target systems | Toxicity / Carcinogenicity classification | Ref. |
|---|---|---|---|---|---|
| Formaldehyde | Propylene glycol and glycerine thermal degradation | CH2O | Mucosal irritation, central nervous system impairment (cognitive/memory deficits), cellular and DNA damage | Known human carcinogen (Group 1 IARC) | (11, 14, 16, 44) |
| Acrolein | Vegetable glycerine thermal decomposition | C3H4O | Severe bronchial and ocular irritation, toxic damage to cardiac tissue and airway epithelium | Potent respiratory and cardiac toxicant | (11, 16, 18) |
| Propylene oxide | Propylene glycol heating | C3H6O | DNA adduct formation, epithelial damage, systemic toxicity | Likely human carcinogen | (17, 29) |
| Glycidol | Glycerine thermal degradation | C3H5O2 | Mutagenic activity, oxidative DNA damage | Carcinogenic compound | (17, 18) |
| Heavy metals (Ni, Cd, Cr, Pb) | Degradation of heating coil/elements | Ni, Cd, Cr, Pb | Systemic inflammation, endothelial dysfunction, increased long-term oncological risk | Toxic metals / carcinogens | (20) |
| Nicotine (when present) | Concentrated e-liquid additive / salts | C10H14N2 | Adrenaline release, acute hypertension, tachycardia, endothelial dysfunction, hippocampal alteration | Potent psychoactive / cardiovascular agent | (12, 30, 33, 35, 40) |
Table 3
Primary vaping-related pulmonary conditions and associated chemical aetiologies
| Disease / pathological condition | Pathogenetically related chemical(s) | Primary clinical manifestations & pathomorphology | Target airway structure | Ref. |
|---|---|---|---|---|
| E-cigarette or vaping-associated lung injury (EVALI) | Vitamin E acetate (used with THC), thermal decomposition products | Acute shortness of breath, fever, hypoxia, diffuse alveolar damage, lipid-laden macrophages | Distal parenchyma and alveoli | (24, 26, 30) |
| Obliterative bronchiolitis (“Popcorn Lung”) | Diacetyl (flavouring agent) | Fibrotic scarring, luminal narrowing, irreversible airway obstruction | Small airways / bronchioles | (27) |
| Lipoid pneumonia | Exogenous oils / Fatty substances | Exogenous lipid accumulation, alveolar macrophage activation, localised parenchymal inflammation | Alveolar spaces | (28) |
| Primary spontaneous pneumothorax | Inhaled aerosol toxicants & pressure changes | Accumulation of air in the pleural cavity, subpleural bleb rupture, sudden lung collapse | Pleural space | (39) |
| Suppressed innate immune function | General vape aerosol components | Microfilament (actin) dysregulation, neutrophil immobilisation, impaired bacterial clearance | Pulmonary immune cells (neutrophils) | (31) |