Ceramides are lipids that are naturally found in the skin. They provide barrier functions to the skin. This means that they prevent moisture from leaving the skin. Therefore, the skin stays nicely moisturized. Additionally, they help prevent harmful environment pathogens from penetrating the skin.

There are other factors that contribute towards proper skin barrier functions such as cholesterol, free fatty acids and etc. They play an important role in proper skin function. 

There is a reason to believe that skin disorders which lean toward the drier side, have limited barrier functions. Therefore, adding ceramides to creams and lotions helps. However, not all ceramides work the same and not all ceramides are great for the skin barrier function. 

People with normal skin mostly have proper-functioning barrier properties. It is important to note, however, that there are a lot of factors that contribute towards healthy and beautiful skin.