Even before you vape them, the chemicals in e-liquids can mix together and turn into new, harmful substances that weren’t listed on the label.
Claim Context
E-liquid ingredients such as cinnamaldehyde and benzaldehyde react with propylene glycol and glycerol during storage to form new toxic compounds called acetals, which are cytotoxic and not accounted for in safety assessments based on original ingredient lists.
“It has been established that aldehyde flavorants such as benzaldehyde, cinnamaldehyde, or vanillin, can react with the common e-liquid solvents PG and GL to form stable acetals within hours... Evidence of potential negative health effects from these reactions is emerging, and transfer of the products to the aerosol, resulting in user exposure to these toxicants, has been demonstrated.”
Evidence from Studies
No evidence studies found yet.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
That acetal formation from flavorant-solvent reactions is a widespread phenomenon across e-liquids and consistently linked to cytotoxicity.
A systematic review of all published chemical analyses of e-liquids stored under ambient and accelerated conditions, identifying and quantifying acetal formation and correlating with in vitro cytotoxicity data across 50+ flavorant-solvent combinations.
That inhaling aged e-liquids (with acetals) causes greater lung damage than fresh e-liquids in humans.
A double-blind, crossover RCT with 20 healthy volunteers inhaling aerosols from freshly prepared vs. 7-day-aged e-liquids containing cinnamaldehyde/PG, measuring bronchoalveolar lavage cell counts and inflammatory markers.
That users of e-liquids stored for >1 week have higher biomarkers of oxidative stress than users of freshly mixed liquids.
A prospective cohort of 500 e-cigarette users tracking e-liquid storage time (fresh vs. >7 days), with weekly urine samples for acetal metabolites and biomarkers of oxidative damage (8-OHdG, MDA), controlling for flavor and device use.
That patients with unexplained lung injury have higher levels of acetal metabolites in biological samples than controls.
A case-control study of 80 patients with idiopathic lung injury and 160 controls, measuring urinary and serum levels of PG/GL-acetal metabolites via LC-MS/MS and correlating with e-liquid storage history.
Consensus that e-liquid safety assessments must include stability and reaction product testing.
A consensus statement from the International Organization for Standardization (ISO) and FDA recommending mandatory testing for acetal formation in e-liquids prior to market approval.