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Research Results From Studies on Propylene Glycol

The main component of e-liquid used in e-cigarettes is Propylene Glycol (PG). There is much research on inhalation of vaporized PG.

There are studies on PG dating back to the 1940's. In fact, it has been used extensively in situations where it would be inhaled in the US since the 1950’s. It has been used in medical devices such as asthma inhalers, as an air disinfectant in places like hospitals and restaurants, and even in hundreds of thousands of entertainment venues such as bars and theaters, since it is the substance used to create fog in fog machines.

Below are the studies on propylene glycol with explanations as to what the study is about along with some quotes from the articles and a link directly to each article in case you would like to read the entire article.

What is Propylene Glycol?

Here are a few quotes from the 2007 EPA re-registration decision approving the use of propylene glycol in places like hospitals and food establishments:

"Propylene glycol is used in air sanitization and hard surface disinfection and dipropylene glycol is used in air sanitization."

"Propylene glycol and dipropylene glycol were first registered in 1950 and 1959, respectively, by the FDA for use in hospitals as air disinfectants."

"Indoor Non-Food: Propylene glycol is used on the following use sites: air treatment (eating establishments, hospital, commercial, institutional, household, bathroom, transportational facilities); medical premises and equipment, commercial, institutional and industrial premises and equipment; laundry equipment; hard non-porous surface treatments (bathroom facilities); automobiles; air conditioning filters; pet treatment, including cats, dogs, and caged birds; environmental inanimate hard surfaces; garbage containers/storage."

"Target Pests: Odor-causing bacteria, Fleas, Mites, Red lice, Animal pathogenic bacteria (G- and G+ vegetative), Shigella bacteria, Pasteurella bacteria, Listeria bacteria, Herpes Simplex I and II, Animal viruses, Influenza Virus A2, Aspergillus Niger Fungus, Mold/Mildew, Pseudomonas SPP., Shigella Flexneri, Shigella Sonnei."

"General Toxicity Observations
Upon reviewing the available toxicity information, the Agency has concluded that there are no endpoints of concern for oral, dermal, or inhalation exposure to propylene glycol and dipropylene glycol. This conclusion is based on the results of toxicity testing of propylene glycol and dipropylene glycol in which dose levels near or above testing limits (as established in the OPPTS 870 series harmonized test guidelines) were employed in experimental animal studies and no significant toxicity observed."

"Carcinogenicity Classification
A review of the available data has shown propylene glycol and dipropylene glycol to be negative for carcinogenicity in studies conducted up to the testing limit doses established by the Agency; therefore, no further carcinogenic analysis is required."

And there is much more information in the full document linked below: http://www.epa.gov/oppsrrd1/reregistration/REDs/propylene_glycol_red.pdf

Here is a link to a Time article about propylene glycol’s germicidal properties when inhaled, published in 1942.

They determined that inhaling Propylene Glycol in levels which were significantly higher than would be common under any circumstances did not have any ill effects on the monkeys used for the study. The only significant effect they noted was weight gain.

http://www.time.com/time/magazine/article/0,9171,932876,00.html

This article is about a study done (in the 1940's since it is obviously unethical to do before they were aware of the potential results!) where PG vapors were emmitted into a children's convalescent home.

Quote fron this article:
"The report of the 3 years' study of the clinical application of the disinfection of air by glycol vapors in a children's convalescent home showed a marked reduction in the number of acute respiratory infections occurring in the wards treated with both propylene and triethylene glycols. Whereas in the control wards 132 infections occurred during the course of the three winters, there were only 13 such instances in the glycol wards during the same period."

http://www.ajph.org/cgi/reprint/36/4/390.pdf

Here is an incredibly long list of air sanitizing products in current commerce based on propylene glycol, many used in hospitals as approved by the EPA in the above PDF:

http://www.scorecard.org/chemical-profiles/pesticides.tcl?edf_substance_id=57-55-6

Here is an article about long-term exposure of significantly high levels of PG vapor in monkeys and rats.

"With a view to determining the safety of employing the vapors of propylene glycol and triethylene glycol in atmospheres inhabited by human beings, monkeys and rats were exposed continuously to high concentrations of these vapors for periods of 12 to 18 months. Equal numbers of control animals were maintained under physically similar conditions. Long term tests of the effects on ingesting triethylene glycol were also carried out. The doses administered represented 50 to 700 times the amount of glycol the animal could absorb by breathing air saturated with the glycol.

Comparative observations on the growth rates, blood counts, urine examinations, kidney function tests, fertility and general condition of the test and control groups, exhibited no essential differences between them with the exception that the rats in the glycol atmospheres exhibited consistently higher weight gains."

http://jpet.aspetjournals.org/cgi/content/abstract/91/1/52

Article on the repeated exposure of rats to PG suggesting low priority for further study due to lack of ill effects.

The first few lines of this study say:
"Propylene glycol (PG) is not acutely toxic. The lowest oral LD50 values range between 18 and 23.9 grams (5 different species) and the reported dermal LD50 is 20.8 grams. PG is essentially nonirritating to the skin and mildly irritating to the eyes."

http://www.inchem.org/documents/sids/sids/57-55-6.pdf

Here is a link to a study showing the safety of propylene glycol as the carrier for inhaled Cyclosporine, for lung transplant patients. Propylene Glycol is used as a drug delivery system, even for patients who have pulmonary complications and whose lungs are compromised specifically because of the germicidal and virucidal properties of the substance.

"There were no respiratory or systemic effects of high doses of propylene glycol relative to air controls. These preclinical studies demonstrate the safety of aerosolized cyclosporine in propylene glycol and support its continued clinical investigation in patients undergoing allogeneic lung transplantation."

http://www.liebertonline.com/doi/abs/10.1089/jam.2007.0626

This article explains that the Entertainment and Services Technology Association hired two independent companies to test the toxicology of propylene glycol in vaporized form in a work environment.

http://www.esta.org/tsp/
working_groups/ FS/cihintro.htm

"The Cohen Group report and the HSE Consulting report are not identical documents, but are substantially congruent in their findings. Both reports state that all of the chemicals they studied (glycerin and five dihydric alcohols) are of low toxicity. Some of the chemicals are of such low toxicity that no maximum allowable concentrations have ever been established, even though they are used in a wide variety of industrial applications. A few of the chemicals have permissible exposure limits defined by a variety of governmental bodies in the US, UK and Germany, but these exposure limits are believed to be higher than the levels needed to produce a heavily fogged theatrical environment. Neither report gives any indication that performance environments should be evaluated in a manner different than that used for other industrial work sites. "

Below are links to the independent studies completed for the ESTA.

http://www.esta.org/tsp/working_groups/FS/docs/cohen.pdf
Statement from the Cohen Study:
"Prolonged and repeated inhalation of triethylene glycol and propylene glycol concentrations well above those present in high-density fog theatrical productions has been repeatedly demonstrated to not pose a health hazard to human subjects. Both glycols have generally been found to be not irritating to the eyes and skin, although splashing the pure compound into the eye may produce transient irritation."

http://www.esta.org/tsp/working_groups/FS/docs/HSE.pdf
Statement from HSE study in which PG referes to Propylene Glycol:
"PG, G, and TEG’s toxicity data appears to be well studied and demonstrates low occupational hazards."

In reference to fog machines, mild throat and eye irritation were only observable symptoms.

"After exposure to PG mist for 1 minute tear film stability decreased, ocular and throat symptoms increased, forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) was slightly reduced, and self rated severity of dyspnoea was slightly increased. No effect was found for nasal patency, vital capacity (VC), FVC, nasal symptoms, dermal symptoms, smell of solvent, or any systemic symptoms. "

http://oem.bmj.com/content/58/10/649.abstract

CDC Toxicity of Propylene Glycol

"In contrast to ethylene glycol, a potent cause of acute toxicity in humans, propylene glycol is a “generally recognized as safe” (GRAS) additive for foods and medications. Propylene glycol rarely causes toxic effects, and then only under very unusual circumstances."

http://www.atsdr.cdc.gov/csem/csem.asp?csem=12&po=14

Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants

"PG is commonly used as an additive in cosmetics and in medicinal agents. It is thought to have low toxicity and is used as a vehicle for intravenous (IV) medications, topical medications, and cosmetics. The Food and Drug Administration considers it safe for use in medication and cosmetics. It is also antibacterial, which makes it useful as a preservative and disinfectant. PG is the principal component of aircraft deicing and anti-icing fluids and of motor vehicle antifreeze."

http://books.nap.edu/openbook.php?record_id=12529&page=314

Product Safety Assessment (PSA): Propylene Glycol

"Inhalation of the PG vapors appears to present no significant hazard in ordinary applications. "

"PG does not cause sensitization and shows no evidence of being a carcinogen or of being genotoxic"

http://www.dow.com/productsafety/finder/prog.htm