Sodium PCA and the natural moisturising factor
Skin makes its own humectant system. Sodium PCA and free amino acids are attempts to top it up rather than to add something foreign.
What NMF is
Natural moisturising factor is the collection of water-soluble compounds inside corneocytes that holds water in the stratum corneum. It is roughly 40% free amino acids, 12% pyrrolidone carboxylic acid (PCA), plus lactate, urea, sugars and inorganic ions. Most of it derives from enzymatic breakdown of filaggrin as corneocytes mature.
NMF is depleted by surfactants, low humidity, over-cleansing and ageing, and its loss is one of the mechanisms behind dry, tight-feeling skin. Filaggrin mutations, which impair NMF production, are associated with atopic dermatitis — evidence of how consequential this system is.
Sodium PCA
The sodium salt of pyrrolidone carboxylic acid, and one of the most hygroscopic humectants available. Because it is a native NMF component, applying it is replenishment rather than substitution. It is also non-irritating and pH-compatible with most formulations. Vegalab uses it in the Hydrating NanoSerum alongside ectoin and ceramides — a coherent trio addressing water binding, water organisation and barrier lipids respectively.
Amino acids and related components
Arginine, serine, glycine and alanine all appear as NMF constituents, and arginine in particular appears in the Youlief DIA serums at 1.3%, though partly as a pH adjuster. Betaine, trehalose and lactate contribute by related mechanisms — see the humectants page.
Why this framing is useful
It reframes hydration accurately. A moisturiser is not adding water to skin; it is either supplying humectants that hold water, occlusives that stop it leaving, or barrier lipids that restore the structure keeping it in. NMF-based ingredients are in the first category, and understanding that makes the layering logic obvious rather than ritualistic.
What does Sodium PCA and the natural moisturising factor not do?
Topical NMF components do not restore filaggrin function or correct the underlying cause of depletion. Humectants are paired with occlusives because evaporation, not the humectant itself, governs whether hydration is retained.
References
- The concentration of pyroglutamic acid in normal and psoriatic epidermis, determined on a microgram scale by gas chromatography
- Filaggrin breakdown to water binding compounds during development of the rat stratum corneum is controlled by the water activity of the environment
- Caspase-14 Is Required for Filaggrin Degradation to Natural Moisturizing Factors in the Skin
- Levels of filaggrin degradation products are influenced by both filaggrin genotype and atopic dermatitis severity
- Retaining Skin Barrier Function Properties of the Stratum Corneum with Components of the Natural Moisturizing Factor - A Randomized, Placebo-Controlled Double-Blind In Vivo Study