Propylene glycol - a harmless substance
Propylene glycol is harmless when taken internally; its oxidation
yields pyruvic and acetic acids.
Propylene glycol is used as emulsifier in foods and as humectant and
solvent in pharmaceuticals.
The Merck Index, 12-th edition, 1996.
Pyruvic and acetic acid are natural intermediates in human metabolism:
pyruvic acid - in sugar metabolism
acetic acid (common name: vinegar) - in fatty acid and carbohydrate
metabolism