An interesting Case Study by Xenios Zonias & Marioxuana on Vaping incredients.

1 What is propylene glycol?

Propylene glycol is a synthetic liquid substance that absorbs water. Propylene glycol is also used to make polyester compounds, and as a base for deicing solutions. Propylene glycol is used by the chemical, food, and pharmaceutical industries as an antifreeze when leakage might lead to contact with food. The Food and Drug Administration (FDA) has classified propylene glycol as an additive that is "generally recognized as safe" for use in food. 

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It is used to absorb extra water and maintain moisture in certain medicines, cosmetics, or food products. It is a solvent for food colors and flavors, and in the paint and plastics industries. Propylene glycol is also used to create artificial smoke or fog used in fire-fighting training and in theatrical productions. Other names for propylene glycol are 1,2-dihydroxypropane, 1,2-propanediol, methyl glycol, and trimethyl glycol.

Source:
https://www.atsdr.cdc.gov/phs/phs.asp?id=1120&tid=240#:~:text=Propylene%20glycol%20is%20a%20synthetic,lead%20to%20contact%20with%20food.
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ATSDR - Public Health Statement: Propylene Glycol
Propylene glycol is a synthetic liquid substance that absorbs water. Propylene glycol is also used to make polyester compounds, and as a base for deicing solutions. Propylene glycol is used by the chemical, food, and pharmaceutical industries as an antifreeze when leakage might lead to contact with food.
www.atsdr.cdc.gov

Is propylene glycol bad for lungs?
In addition to the problem of vaping leading to smoking, the Pediatrics study found that the volatile chemicals in e-cigarettes, like propylene glycol and glycerol, can form carcinogenic compounds when heated, and that those compounds were found in the urine of the 16 year olds who were tested.
High doses of propylene glycol (six grams per kilogram or more) have been found to cause kidney damage in many species and physical deformities in baby chickens. But the FDA believes it's safe at the levels being used.

Legality in Europe ?
Turns out, propylene glycol is illegal in Europe, but perfectly okay in the United States. The makers of Fireball now have two versions they sell, one containing this ingredient that gets sent out to the United States, and another without that goes to Europe

A few months ago, the makers of Fireball suffered a controversy when some European countries began recalling the drink for including propylene glycol, an ingredient found in antifreeze. Turns out, propylene glycol is illegal in Europe, but perfectly okay in the United States.
The makers of Fireball now have two versions they sell, one containing this ingredient that gets sent out to the United States, and another without that goes to Europe. You may be scratching your head thinking "Huh?" Why would they send people in the U.S. a different product?
Despite efforts to regulate food safety, the FDA allows many ingredients in the U.S. that have been banned in other countries. Although these ingredients have been deemed safe or are said to need further testing, you may want to consider eliminating them from your diet, as there usually good reasons these other places have made them illegal.
Next time you're purchasing a food product, look out for these potentially dangerous ingredients that have been banned in other countries.

SOURCE:
​https://www.bustle.com/articles/55096-7-ingredients-banned-in-other-countries-that-are-legal-in-the-us

These are the notorious "E'" numbers in food additives, cosmetics and Pharmacology that imply you are about to ingest Propylene Glycerol:
Propylene glycol (IUPAC name: propane-1,2-diol), according to the National Library of Medicine and Agency for Toxic Substances and Disease Registry, is a synthetic liquid substance that absorbs water.[4] It is labelled an organic compound in chemistry due to its carbon attributes (Which is a lie as it is man made). Its chemical formula is CH3CH(OH)CH2OH. It is a viscous, colourless liquid, which is nearly odourless but possesses a faintly sweet taste. Containing two alcohol groups, it is classed as a diol. It is miscible with a broad range of solvents, including water, acetone, and chloroform. In general, glycols are non-irritating and have very low volatility.[5]
It is produced on a large scale primarily for the production of polymers. In the European Union, it has the E-number E1520 for food applications. For cosmetics and pharmacology, the number is E490. Propylene glycol is also present in propylene glycol alginate, which is known as E405. Propylene glycol is a compound which is generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) under 21 CFR x184.1666 and is also approved by FDA for certain uses as an indirect food additive. Propylene glycol is approved and used as a vehicle for topical, oral and some intravenous pharmaceutical preparations in U.S. and in Europe.
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