Ceramides are a family of lipids that consist of two long chain fatty acids linked to one another by an amide group.
Ceramides are one of the 3 key classes of lipids that form the lamellar membranes coating the external surfaces of the cells of the outermost layer of skin, the stratum corneum. Normally, each of these 3 key lipids is present in equal proportions (‘equimolar’). A deficiency of any one of the 3 key lipids results in a leaky skin barrier.
Ceramides in the stratum corneum derive from 2 sources; 1) the breakdown of a phospholipid called sphingomyelin, which is present in the plasma membrane of cells of the underlying epidermis; and 2) the breakdown of sugar-containing lipids called glycosphingolipids. The generation of ceramides from these precursor lipids takes place in the stratum corneum through the action of the enzymes, sphingomyelinase and beta-glucocerebrosidase, respectively.
The common skin disease, atopic dermatitis or eczema, exhibits a deficiency of ceramides and a poor permeability barrier. A much rarer condition called Type 2 Gaucher disease (due to an inherited, very severe deficiency of the enzyme beta-glucocerebrosidase) results in a barrier defect and a scaling disorder, in other words, a form of ichthyosis.