By Ken Fry, Founder & CEO, Terps USA

SHORT ANSWER

PEG 200's flash point is a real physical property, but it cannot answer the vaping-safety question by itself. Flash point concerns ignition of vapors under specified test conditions. Vaping risk is primarily an aerosol-chemistry and inhalation-toxicology question. Those are not the same thing.

Why the old flash-point argument is tempting

If a vape operates near a published flash point, it is easy to assume the number tells us whether the liquid is “burning.” But a flash point is not a boundary between safe and unsafe use, and it is not a thermal-decomposition threshold. A substance does not need to ignite in order to generate degradation products when heated.

Combustion and decomposition are different

Autoignition temperature, flash point and thermal degradation describe different phenomena. For vaping, the important question is what chemicals are present in the aerosol at the actual coil, power, liquid-supply and puffing conditions — not simply whether the bulk liquid catches fire.

What the 230°C experiment still tells us

A finding that PEG generates formaldehyde under a 230°C test condition should be taken seriously as evidence of thermal degradation under that condition. The appropriate follow-up is not to dismiss it because PEG did not combust. It is to determine how emissions change across representative device conditions and whether the tested condition resembles consumer exposure.

What the inhalation study can and cannot add

A published two-week nose-only inhalation study of PEG 3350 in rats reported no exposure-related toxicity at the tested concentrations. That is useful toxicology evidence for PEG 3350 under those study conditions, but PEG 3350 is not PEG 200, and a short-duration animal study does not establish the safety of every PEG molecular weight or heated aerosol formulation.

The chemistry-first conclusion

Flash-point math is not a substitute for aerosol chemistry. The defensible way to evaluate PEG is to match the exact material, heating condition, aerosol composition, dose and inhalation evidence to the product and exposure being discussed.

FAQ

Does PEG 200’s flash point tell you whether it is safe to vape?

No. Flash point describes the conditions under which vapors can ignite in a standardized test. It is not a toxicology threshold and does not tell you when thermal-degradation products begin to form.

Is flash point the same as decomposition temperature?

No. Ignition, combustion and thermal decomposition are different processes. A material can undergo chemical degradation without catching fire.

What evidence is more relevant to PEG vaping risk?

Relevant evidence includes aerosol chemistry under representative device conditions, the identity and amount of thermal-degradation products, inhalation toxicology for the specific PEG grade and molecular weight, dose, and duration of exposure.

Sources

1. Fry, K. (2026). “The Science of Safety: Debunking the Myths Surrounding Propylene Glycol and Polyethylene Glycol in Vaping Applications.” Terps USA Research. DOI: 10.5281/zenodo.21005414

2. Baer, F. A., et al. (1989). Two-week aerosol inhalation study on polyethylene glycol (PEG) 3350 in F-344 rats. Fundamental and Applied Toxicology, 12(2), 258–263. PMID: 2714207.

This article is for informational and industry education purposes only. Terps USA products do not contain THC or CBD. These statements have not been evaluated by the FDA. Readers are encouraged to consult the cited primary sources directly.