Natural Moisturising Factor: Your Skin's Built-In Moisturiser (and How to Copy It)
Your skin had moisturiser long before humans invented jars. Inside the cells of the skin's outer layer is a mix of small, water-loving molecules called natural moisturising factor (NMF). It's a big reason healthy skin stays soft and flexible, and it's the blueprint for some of the gentlest, most effective hydrators you can formulate with.
What NMF is made of
NMF is a blend of small, water-soluble compounds made inside skin cells as a protein called filaggrin breaks down (Rawlings & Harding, Dermatologic Therapy, 2004). A widely cited breakdown of its composition looks roughly like this (Fowler, Practical Dermatology, 2012):
- Free amino acids: about 40%
- PCA (pyrrolidone carboxylic acid): about 12%
- Lactate: about 12%
- Urea: about 7%
- Plus sugars, minerals and other small molecules
Each of these holds water, and together they keep the outer layer of skin hydrated from the inside.
When NMF runs low
- Genetics: some people carry variants of the filaggrin gene that reduce NMF. A landmark study linked common filaggrin variants (carried by around 9% of people of European descent) to a much higher risk of atopic eczema (Palmer et al., Nature Genetics, 2006). The specific variants and how common they are differ between populations around the world.
- Season: research has found lower NMF levels in winter than in summer (Dermatology Times).
- Over-washing and harsh surfactants can rinse NMF out of the skin's surface. Another reason for a gentle cleanser.
Skin-identical humectants: copying the blueprint
The smart idea is to give skin back the same kinds of molecules it uses itself:
- PCA: Sodium PCA is the classic choice. Our dictionary entry lists 2–10%. The US Cosmetic Ingredient Review found PCA and sodium PCA safe as used in cosmetics, with the caveat that they shouldn't be combined with nitrosating agents (CIR, 1999).
- Lactate: Sodium Lactate is a strong humectant that also helps buffer pH.
- Urea: Urea at moisturising levels (our body care post explains how its job changes with concentration).
- Amino acids: Serine, Glycine, Alanine, Proline and Arginine, or a ready blend like Silk Amino Acids.
- Supporting hydrators: Glycerin (skin moves it through its own channels; see our glycerin post), Betaine and Trehalose.
An "NMF-style" hydrating serum blueprint
- Water phase with a mix of humectants: glycerin, sodium PCA, sodium lactate, a small amount of urea and an amino acid blend
- A light gel base (xanthan or a pre-neutralised carbomer)
- A touch of Panthenol for comfort
- pH about 5–5.5, plus a broad-spectrum preservative
- Follow with a moisturiser containing barrier lipids. Humectants pull water in, and lipids keep it there (see Ceramides 101).
Tip: a blend of several humectants at modest levels usually feels nicer (and less sticky) than one humectant at a high level, which is exactly how skin does it.
Explore NMF & Skin-Identical Actives, Humectants and Proteins & Amino Acids.
Eczema is a medical condition. If you have it, a dermatologist can help build the right routine.