*Adapted with permission from a presentation given during the 2020 Anti-ageing Conference.

Skin lipids, including those of both sebaceous and keratinocyte origin, cover the surface of skin. Their apparent composition varies and is subject to the chosen method of sampling.

Lipids produced by the epidermal cells are a mixture of long chain ceramides, free fatty acids and cholesterol. They represent a minor fraction of the total extractable surface lipids on areas rich in sebaceous glands. Lipids of epidermal origin seal the stratified corneocytes on the stratum corneum in a relationship similarly to the “mortar” in the brick-and-mortar skin structure model.

Sebaceous lipids, on the other hand, are mainly non-polar triglyce­rides, wax esters and squalene. They are secreted as sebum due to the holocrine activity of the sebaceous gland and eventually released to the top of the skin, where they coat the surface, as well as hair shafts. The composition of sebaceous lipids is exceptional—e.​g., sapienic acid and its metabolites plus the wax esters—and rather intriguing because they are not found anywhere else in the human body. Furthermore, elevated sebum excretion is a major factor involved in the pathophy­siology of acne.

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By Apostolos Pappas, Ph.D., Rutgers University, New Brunswick, NJ USA and Nogra Pharm, Dublin – April 30, 2021