Naturally occurring, long chains of skin lipids (fats) that are major structural components of the skin’s outer layers. Skin as a barrier system inhibits water movement via its extracellular matrix, which has a unique composition of 50% ceramides, 25% cholesterol, and 15% free fatty acids. Together, these lipids form what researchers refer to as "crystalline lamellar structures" (Sources: Journal of Lipid Research, September 2007; Journal of Investigative Dermatology, November 2001, pages 1126–1136; and Experimental Dermatology, October 2005, pages 719–726). Ceramides are necessary for the skin’s water-retention capacity as well as for barrier repair and cell regulation. Adding ceramides to skin-care products can help to restore the skin’s barrier system (Sources: American Journal of Clinical Dermatology, June 2005, pages 215–223; Journal of Dermatological Science, September 2006, pages 159–169; Skin Pharmacology and Applied Skin Physiology, September–October 2001, pages 261–271; and Cutis, December 2005, Supplemental, pages 7–12).
Nine different ceramides have been identified in skin, some of which are used in skin care. On a skin-care product ingredient label, you'll see those listed as ceramide AP, ceramide EOP, ceramide NS, ceramide NP, ceramide NG, phytosphingosine (which can produce numerous ceramides in skin), and sphingosine. The ceramides used in skin care are typically derived from plants or are synthetic, and there is no research showing either form is preferred over the other. However, the chain length of synthetic ceramides can be controlled, while chain length of plant or of animal-derived ceramides cannot be. The benefit of controlling the chain length is a "better fit" when the ceramide chain is applied to skin cells in need of help (Source: Biochmica et biphysica acta, October 2014, pages 2,473-2,483; and Experimental Dermatology, January 2014, pages 45-52).