By Ken Fry, Founder & CEO, Terps USA

SHORT ANSWER

Propylene glycol has a substantial toxicology and use history, but the strongest case for it is not a blanket statement that “FDA says inhaling PG is safe.” FDA GRAS status applies to specified food uses. Questions about inhalation need inhalation-specific evidence, and that evidence should be described with its actual limits.

GRAS is real — and often misused

Propylene glycol is used in foods and has GRAS status for specified uses. That is meaningful regulatory history, but exposure route matters in toxicology. Eating a substance and repeatedly inhaling an aerosol are not the same exposure. GRAS should therefore be part of the background, not the conclusion of an inhalation-safety argument.

What modern inhalation evidence adds

A 2024 study exposed rats nose-only to a 50:50 PG/VG aerosol at a target concentration of 3 mg/L for six hours per day over 28 days. The researchers reported minimal biological effects and no signs of toxicity in conventional clinical observations, blood analyses and histopathology. They also identified changes in molecular pathways through transcriptomic, proteomic and metabolomic analyses, including pathways related to inflammatory response and lung function.

Why that is more useful than a slogan

The study does not prove that all PG-containing vapor products are harmless. It does provide controlled inhalation data under a defined exposure. Device temperature, formulation, concentration, duration and co-ingredients can all change the exposure profile.

The evidence-based position

PG should neither be condemned by association with the 2019 EVALI outbreak nor declared universally safe because it has a long history of use. The better standard is exposure-specific evidence: what was inhaled, at what concentration, for how long, and what biological effects were measured?

FAQ

Does FDA GRAS status mean propylene glycol is approved as safe to inhale?

No. GRAS status concerns specified food uses and should not be presented as an FDA determination of inhalation safety. Inhalation questions need to be evaluated using inhalation-specific evidence.

What did the 2024 PG/VG inhalation study find?

In a 28-day rat nose-only exposure study of a 50:50 PG/VG aerosol, conventional clinical observations, blood analyses and histopathology found minimal biological effects and no signs of toxicity, while multi-omics analyses identified pathway changes that the authors described as early evidence relevant to potential respiratory effects.

Does the existing evidence prove long-term vaping with PG is risk-free?

No. The evidence can inform risk assessment, but a subacute animal study and historical uses do not establish that every formulation, device, dose or lifetime exposure is risk-free.

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. Chu, M., et al. (2024). Conventional and multi-omics assessments of subacute inhalation toxicity due to propylene glycol and vegetable glycerin aerosol produced by electronic cigarettes. Ecotoxicology and Environmental Safety, 271, 116002. DOI: 10.1016/j.ecoenv.2024.116002.

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.