Science:

A well understood substance

Chemically, propylene glycol has a very simple structure:

The two parts of the molecule, the alcohol groups ("OH", likes water) and the hydrocarbon backbone ("CH", likes oil), represent fundamental chemical characteristics. Their behaviour both in industrial processes, as well as in the human body or in the environment, is well understood.

In the human body, propylene glycol is quickly metabolised and excreted. Its metabolic pathway is comparable to that of sugar: propylene glycol is rapidly converted into lactic acid, in a similar manner to what happens with sugar (energy) in the muscles during sports. It is the lactic acid in your muscles which makes them ache following intensive exercise. Lactic acid, the metabolite of propylene glycol, therefore, is also naturally present in our bodies. It is excreted via urine.

In the environment, tests have shown that propylene glycol is readily biodegradable.

Studies show that propylene glycol has a very low degree of toxicity. From a toxicological point of view, alcohol is more toxic than the same amount of propylene glycol.