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E-Cigarettes - No Toxic Effects from Inhaled Propylene Glycol Aerosol

Posted Aug 24 2011 6:09pm
One of the key ingredients in many e-cigarette liquids is propylene glycol (PG), described by Wikipedia ( here ) as a “colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste…” The entry also explains that PG is used “as a moisturizer in medicines, cosmetics, food, toothpaste, shampoo, mouth wash, hair care and tobacco products…, in smoke machines to make artificial smoke for use in firefighters' training and theatrical productions” and “as a moisture stabilizer (humectant) for snus” among many other applications.

A new study provides valuable information about the toxicological profile of inhaled PG aerosols in laboratory animals; it also provides an excellent general review of the agent. The authors are Michael Werley, a scientist at Altria, and colleagues from Charles River Laboratories (Scotland), WIL Research Laboratories, Battelle Memorial Institute and Virginia Commonwealth University. It was published in the journal Toxicology (abstract here ).

The investigators exposed rats and dogs to high concentrations of PG aerosol for up to 28 days, followed by comprehensive systemic evaluations, especially involving the respiratory system.

They report, “In general, these studies confirmed the relatively low toxic potential of [aerosol] PG, administered by various dose routes, including the inhalation route…in the dog, no histopathological effects on the [larynx, trachea and lung] tissues were observed.” The investigators noted decreases in some assessments of red blood cells in dogs treated for 28 days, but “these effects were not clinically significant in the dog and had no effect upon their activity of health”, and “the values still within the normal historical ranges for dogs of this age, strain and sex.”

Werley and colleagues added that, “overall, PG inhalation exposure in rats and dogs produced quite limited toxicological findings, and allowed us to conclude that [aerosol] PG exposures could be conducted safely in man by the inhalation route…”

This study assessed the effects of short-term exposure to PG vapor, but the effects of long-term (months or years) exposure are unknown and unknowable. However, it provides valuable information for e-cigarette users and policy makers. First, even high concentrations of PG vapor don’t have any measurable harmful effects, which is fully consistent with its designation by the FDA as “generally recognized as safe” as a food additive for all food categories up to 2% ( here ). Just as important, there will be no impact on bystanders from “second-hand” exposure to e-cigarette vapor, if it occurs at all.

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