What is Propylene Glycol?

The opinions in this post, while scientifically informed, are not making claims about safety and health. This is not intended to be medical advice.

Now that that's out of the way.

As a juicetender, you hear a lot about what the people in the street are concerned with regarding safety in vaping. As someone who studied Biochemistry and also works in a field tangential to it, I feel as if I have a unique perspective to offer. One thing I often hear customers express concerns about is the use of PG, a.k.a. Propylene glycol.

Things I hear:

  • It's in antifreeze!
  • It sounds scary and synthetic.
  • It just ain't natural.

I think these claims deserve a bit more examination. Let's start with the name.
Propylene glycol is a common name (a nerdy version of slang) for the chemical Propane-1,2-diol. The Propane-1,2-diol name is the recognized IUPAC (team of nerds who are the authority for naming chemicals) for propylene glycol. While the common name is clearly influenced by the IUPAC name, let's look at a list of IUPAC names for some "all-natural" stuff.

What we call it Common Name  IUPAC Name
Sugar Glucose (2R,3S,4R,5R)-2,3,4,5,6-Pentahydroxyhexanal
Vanilla Extract Vanillin 4-Hydroxy-3-methoxybenzaldehyde
Vitamin C Ascorbic Acid

(R)-3,4-dihydroxy-5-((S)- 1,2-dihydroxyethyl)furan-2(5H)-one


As you can see, a lot of normal, every-day use items have scary looking common names and IUPAC names.

Before we can move past that and move toward examining propylene glycol itself, we should ask ourselves a question.

Why is propylene glycol used in vape juice in the first place?

Well, this is a semi-complicated question to answer without boring you to death, but the gist of it is this: PG is hygroscopic, meaning water molecules cling to it. It has a high combustion point, so rather than burning or combusting it, it is vaporized at higher temperatures. It also acts as a vehicle that carries the flavor and nicotine in vape juice with it when it vaporizes.


Ok, now onto propylene glycol itself. I know what you're going to ask. Is it used in anti-freeze? The answer is yes, propylene glycol is used in NON-TOXIC, ENVIRONMENTALLY FRIENDLY, anti-freeze that is intended to be safe if a child or animal accidentally slurps it up. It is used in this way because of the properties we discussed earlier. It is not the same as traditional anti-freeze which is it's evil cousin ethylene glycol. You eat salt right? Sodium chloride? Well if you ate just pure sodium (without the chloride) you'd be pretty unhappy. A single change in the composition or even the structure of a molecule can drastically change how it behaves.

See textbook example: https://en.wikipedia.org/wiki/Thalidomide

Ethylene glycol is bad for the environment and bad for pretty much every living thing because of it's effects on metabolic processes. (Fun fact: it acts on the same pathway as alcohol, sometimes it is treated with an alcohol IV drip).

Now propylene glycol, propylene glycol is pretty awesome. It is GRAS (Generally recognized as safe) by the FDA as a food additive. Here's a small list of foods containing PG. If you've ever eaten these from a store, you've eaten propylene glycol.

  • Cake Mix
  • Ice Cream
  • Salad Dressing

It's also used as a vehicle for medications in inhalers and about a billion other things.

What do you guys think? Leave a comment below and I'll get back to ya.

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