CeramidesvsGlycerin

Ceramides are sphingolipids comprising a sphingoid base (sphingosine or phytosphingosine) amide-linked to a fatty acid—comprising ~50% of stratum corneum lipids. They integrate into the intercellular lipid matrix between corneocytes, forming the lamellar bilayer structure with cholesterol and free fatty acids that limits transepidermal water loss (TEWL). Optimal molar ratio is ~3:1:1 (ceramides:cholesterol:fatty acids). Topical ceramides (NP/3, AP/6-II, EOP/1) fill gaps from barrier damage by surfactants, retinoids, or inflammation. Cholesterol enables lamellar phase formation; fatty acids provide acidic pH for ceramide packing. Products restoring the complete ratio upregulate barrier repair genes (involucrin, filaggrin, transglutaminase) more effectively. Synthesis occurs via serine palmitoyltransferase and ceramide synthase in keratinocytes.

Glycerin (glycerol) is a small three-carbon polyol (92 Da) that penetrates the stratum corneum via intercellular lipid and transcellular routes. It acts as a humectant through osmotic mechanisms—creating a concentration gradient that draws water from the atmosphere (when humidity >65%) and from deeper epidermal layers. Glycerin upregulates aquaporin-3 (AQP3), a glycerol-permeable water channel in keratinocyte membranes that facilitates water and glycerol transport. It supports the natural moisturizing factor (NMF)—amino acids, lactate, and urea that maintain stratum corneum water-holding capacity. Glycerin modulates keratinocyte differentiation and may enhance lipid lamellae organization. Mild antimicrobial activity occurs through osmotic stress. Clinical studies demonstrate hydration efficacy comparable to or exceeding hyaluronic acid.