PG is a colourless liquid which is slightly sweet to taste. It is a diol and not an oil. It is an humecant with hygroscopic properties and also has antimicrobial properties.
Time Magazine first reported on studies on PG in 1942, unfortunately paywalled now. It’s used in inhaled medications such as NRT, and is generally safe, although a small number of people may be sensitive to it. But the effects of inhaling it are very well understood. PG is non-toxic when ingested even in reasonably large amounts. PG is easily metabolised by the liver into the products of the citric acid metabolic cycle, which are completely non-toxic. Approximately 45 percent of any ingested PG is excreted directly from the body and never even comes into contact with the liver. The elimination half-life for propylene glycol is approximately four hours, and there is no build up over time. We have some pretty good studies into PG toxicity, although a lot of them are animal studies with the usual problems of correlation to humans from these studies. Read one for yourself that was published in 1947 here.
Quoting from the EPA (PDF)
“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.”
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.”
PG is found in a huge variety of products, from asthma inhalers to baby wipes. NRT products to shampoo and toothpaste. Cupcakes, muffins and even coffee syrups. It is pretty much a given that if you’re truly sensitive to it, you’d know already. If you can’t stay in a room where they’re using theatrical fog, then it might be the PG affecting you. If you can breathe without issues or later side effects, you’re probably fine. People who are sensitive to PG should use a high VG juice as standard. Make sure that your chosen ecig will wick a high VG juice though. The most common side effects of PG inhalation are dry mouth, mild sore throat and increased thirst.
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