Glycerin, Vegetable Glycerin
Glycerin is is a component of the skin's own moisturizing system and well tolerated by the skin. It is a byproduct of oleochemistry e.g. by separating plant and animal fat in glycerin and amino acids, propyl can be extracted, which is a byproduct of biodiesel.
In cosmetics, glycerin has strong moisture binding properties, while protecting and regenerating the skin's own barrier function. As such, the skin's elasticity is increased. In addition to surfactant substances (e.g included in some cleansing products), glycerin soothes and reduces skin irritations and skin damage. Glycerin is suitable for dry skin as well as dry hair because it has moisturizing and irritation-alleviating ingredients.
see Heike Käser 2010, "Naturkosmetische Rohstoffe", Linz, Verlag Freya, 3. Edition 2012