Triglyceride

A triglyceride has a simple architecture: a three-armed glycerol core with a fatty acid attached to each arm. Nearly everything sold as an oil or a butter is a mixture of these, and so is much of what skin produces on its own.

The shape is why oils behave as a family. The core is identical in all of them; only the arms change, and they decide melting point, thickness, how quickly the material stops being noticeable and how prone it is to going off. That is how one material is liquid at room temperature and another a solid butter, with no difference in the class of molecule.

It explains some labels too. Caprylic/capric triglyceride is not a plant — it is a triglyceride built from selected short arms because a formulator wanted a light, stable, predictable oil rather than a botanical one. Hardening an oil into a solid also works on the arms rather than the backbone. And a few materials sold as oils are not triglycerides at all: jojoba is a liquid wax, which is why it behaves unlike what it sits beside on a shelf.

Two consequences worth carrying. Skin does not read the plant on the bottle; it meets a set of fatty acids, and unrelated plants with similar arms behave similarly. And a triglyceride is large by skincare standards, part of why oils work on and in the outermost layer rather than far below it.