Glycerin

Glycerin is a simple alcohol that the body makes on its own and that sits at the center of every fat and oil. It works by pulling in water, which is why it shows up in moisturizers, toothpaste, and foods that need to stay soft. On its own it is about as well-established as an ingredient gets: the FDA lists it as generally recognized as safe and as an over-the-counter skin protectant, Europe's food authority re-cleared it, and the cosmetic review panel found it nontoxic and non-irritating. The real-world catch is not glycerin itself but what can be sold in its place. Because a cheap industrial solvent, diethylene glycol, looks and pours like glycerin, it has been illegally substituted into medicines several times over the last century, from a 1937 disaster in the United States to cough syrups that killed children in The Gambia and Indonesia in 2022. That is adulteration with a different, toxic chemical, which is why drug standards cap diethylene glycol at a trace level and why testing the raw material matters. Pure glycerin, the kind in a regulated product, is not the concern. One minor note for skin: at very high strength in very dry air it can pull moisture the wrong way, so it is normally paired with an oil or emollient.