Keratinocytes biosynthesize glucosylceramides, acylglucosylceramides and sphingomyelins, which are potential precursors of ceramides in stratum corneum. Specificly, acylglucosylceramides are unique components comprised of both very long chain fatty acids as the amide-linked fatty acids and as esterified fatty acid linked through the ω-hydroxy group. The one found in the human epidermis consists of two acylglucosylceramide groups, one containing sphingenine and the other containing phytosphingosine with a single double bond. The linoleic acid content as ester-linked fatty acids is very high in human epidermis. We named these acylglucosylceramides contain linoleic acid “epidermosides”; they are key molecules of the epidermal permeability barrier. Epidermosides are the precursors of acylceramides and ω-hydroxy ceramides ; the latter are the major components of the corneocyte lipid envelope. Glucosylceramides and sphingomyelins have structural heterogeneities in the ceramide portion. All ceramide species are derived from glucosylceramides, while a fraction of Cer 2 and Cer 5 come from sphingomyelins.