Ceramides are important for keeping a healthy skin barrier and provide hydration (it prevents water from evaporating from the skin). Ceramides applied to the face can work to some extent if we put it on our faces and can hydrate the skin.

The science: ceramides are waxy lipids found in the outer layer of the skin. Ceramides make up about 30-40% of this outer skin layer. There are many types of ceramides but the base molecular structure is the connection of a fatty acid and a sphingoid base

There are many different versions of ceramides and those vary based on the form of the spingoid base and the fatty acid. 

Here are a few: 

Ceramide 1(EOP; P=phytosphinogosine, EO=fatty acid, in this case its linoleic): used as a binding role in the extracellular matrix. Also plays a vital role in epidermal integrity and storage for linoleic acid. 

Ceramide 3(NP)

Ceramide 6(AP)

Also want to include here sphingoid bases (or sphingosines) which are related to ceramides

A sphingoid base can be found in the skin. There is research that shows it has antimicrobial properties and helps with skin-defense. It could also work against acne-causing bacteria and even could work as an active ingredient in acne-prone skin.