- Four popular nicotine e-liquids produced dramatically less toxicity in human lung cells than cigarette smoke.
- No reactive oxygen species (ROS) – a major marker of oxidative stress – were detected from any flavoured e-liquid aerosol.
- Trace metals and microplastics in the e-liquids were found at very low levels, all below WHO drinking water limits.
- Cigarette smoke caused severe cell damage, including mitochondrial breakdown, while e-liquids preserved cell integrity.
A major new lab study has shown that aerosols from nicotine e-liquids are vastly less toxic than cigarette smoke.
The work, conducted by the Center of Excellence for the Acceleration of Harm Reduction (CoEHAR), strengthens scientific evidence supporting vaping as a lower-risk alternative for smokers.
The research, published in Molecular and Cellular Biochemistry, tested four popular nicotine-rich e-liquids against smoke from an official ‘1R6F’ reference cigarette using a realistic “air-liquid interface” exposure system. This model exposes human bronchial cells to aerosol or smoke in a way that mimics real-world inhalation.
Very low contaminants: metals and microplastics far below safety limits
The study first assessed whether the e-liquids contained contaminants such as heavy metals or microplastics. All four products showed low levels of trace elements and small plastic particles, well below the World Health Organisation (WHO)’s limits for drinking water.
The authors noted: “All tested e-liquids showed very low levels of trace metals and microplastics, with contaminant concentrations below WHO drinking water limits.”
While WHO thresholds relate to ingestion rather than inhalation, the team emphasised that the detected levels were extremely low and unlikely to pose a health concern.
Cigarette smoke caused severe toxicity – e-liquids did not
When researchers exposed lung cells to the aerosols, the contrast between vaping and smoking was striking.
Cells exposed to cigarette smoke experienced major cell death, mitochondrial collapse, and strong oxidative stress. In the standard Neutral Red Uptake toxicity test, cigarette smoke reduced cell viability to just 32 per cent.
By comparison, e-liquids preserved healthy cell function. The study found: “E-liquid aerosol induced significantly reduced cytotoxicity compared to 1R6F regular cigarette smoke, and mitochondrial integrity was preserved.”
Even after 24 hours, lung cells exposed to the four e-liquids maintained over 90 per cent viability, and mitochondrial function remained stable.
Flavoured e-liquids produced no oxidative stress
One of the most important findings concerned reactive oxygen species (ROS), a major driver of smoking-related disease. Cigarette smoke triggered large amounts of ROS, even at low puff exposures.
By contrast, the study reports: “No ROS generation was observed when using flavored e-cigarette aerosol.”
Nicotine-only PG/VG mixtures produced some ROS at very high puff counts, but the flavoured e-liquids – representing real consumer products – did not.
This suggests that the flavour formulations used in the study may help reduce thermal degradation and oxidative reactions during vaporisation.
E-liquids avoided triggering cell apoptosis
Using an Annexin V apoptosis test, the researchers examined whether aerosols triggered programmed cell death. Cigarette smoke caused a dramatic spike in advanced apoptosis, while e-liquids did not.
The paper notes: “No differences in advanced apoptotic cells were shown for PG/VG, PG/VG with nicotine, Sample A, Sample B, Sample C, and Sample D compared to AIR control.”
In other words: vaping aerosols behaved similarly to clean air, while cigarette smoke rapidly pushed cells into irreversible damage.
Mitochondria – critically harmed by cigarettes, preserved by vaping
Mitochondria, the energy centres of cells, were severely damaged by cigarette smoke. Within hours, mitochondria in smoke-exposed cells lost their membrane potential, a key marker of cellular failure.
For e-liquids, the study found: “All products tested did not cause significant reduction in mitochondrial function, except in cells exposed to 1R6F cigarette smoke.”
This suggests vaping aerosols do not trigger the type of energy-system collapse commonly associated with smoking-induced disease.
What this means for harm reduction
The study provides robust, laboratory-based evidence that vaping aerosols produce a fraction of the toxic impact of cigarette smoke, even when tested under stringent, standardised exposure conditions.
The authors concluded: “These results provide evidence of the lower potential toxicity of e-cigarettes compared to tobacco cigarettes in an in vitro model simulating real-world smoke exposure.”
