Natural Moisturizing Factor (NMF)
Natural Moisturizing Factor (NMF) — a group of water-soluble compounds within the outer skin cells that attract and hold moisture, keeping the surface hydrated and supple. It includes amino acids, urea, lactic acid, and other humectant molecules derived largely from the breakdown of the protein filaggrin.
Key points
- NMF is composed of humectant substances such as amino acids, urea, lactic acid, PCA, and various salts.
- Much of NMF is produced as the protein filaggrin is broken down during skin cell maturation.
- It helps the stratum corneum retain water, keeping skin flexible and smooth.
- Low NMF levels are associated with dryness, tightness, and rough texture.
- Some skincare ingredients mimic or replenish NMF components to support hydration.
What is in the mixture
| Component | Approximate share | What it does |
|---|---|---|
| Free amino acids | Around 40% | The bulk of the humectant load; serine and glycine dominate |
| PCA (pyrrolidone carboxylic acid) | Roughly 12% | Made from glutamine; among the strongest water-binders present |
| Lactate | Roughly 12% | Binds water and adds to surface acidity |
| Inorganic salts | Close to 18% combined | Sodium, potassium, chloride, calcium; hold water osmotically |
| Urea | Around 7% | Humectant; at higher levels also softens keratin |
| Sugars and organic acids | Roughly 8% | Glucose, citrate, uric acid — minor but persistent |
| Urocanic acid and traces | A few per cent | Absorbs some UV; adds buffering |
Shares are approximate and differ between published measurements, body sites and individuals.
Where it comes from
NMF is largely a recycling product. As a keratinocyte enters the granular layer it fills with granules of profilaggrin, which is cut into filaggrin units that briefly bundle keratin filaments while the cell flattens into a corneocyte. Once that job is done, a sequence of enzymes dismantles filaggrin into its constituent amino acids, which stay inside the cell.
Those amino acids are then modified: glutamine cyclises to PCA and histidine is converted to urocanic acid. The pool is topped up from elsewhere, with lactate and urea arriving in sweat. The finished mixture sits dissolved in the corneocyte at high concentration, holding water inside the cell so the outer layer stays pliable rather than brittle.
Why humidity changes how much is made
Filaggrin breakdown is not a fixed-rate process. The enzymes responsible respond to the water content of the stratum corneum, degrading filaggrin more actively when the outer layer is relatively dry and slowing when it is not. Skin held in humid air therefore generates less NMF, and skin in dry air more — a loop that partly compensates for the environment.
The compensation has limits. Very dry, cold air removes water faster than the loop can answer, and it cannot run at all if the raw material is missing. Washing is a second constraint: NMF is water-soluble, so it leaches out and must be regenerated by cells already at the end of their working life.
When there is less of it
The clearest case is genetic. Loss-of-function variants in the filaggrin gene reduce or remove the precursor protein, so less NMF is produced from the outset. They are associated with ichthyosis vulgaris and with a raised likelihood of atopic dermatitis, and such skin measures lower in NMF even when it looks unremarkable. Diagnosis belongs with a clinician.
NMF also falls for ordinary reasons: it declines with age as maturation slows, drops in winter, and is depleted by surfactants, solvents and prolonged water contact. Ultraviolet exposure and inflammation interfere with filaggrin processing as well. The result is consistent whatever the cause — a stiffer, duller surface that feels tight soon after washing.
Frequently asked
What happens when NMF levels are low?
Reduced NMF can leave the outer skin layer less able to hold water, contributing to dryness, tightness, and a rough or flaky surface.
Can skincare replenish NMF?
Ingredients like amino acids, urea, glycerin, and lactic acid can supplement NMF components and help the skin retain moisture.
Is NMF the same thing as a humectant?
Not quite. Humectant describes a property that many ingredients share. NMF is a specific mixture the skin makes for itself and keeps inside its own cells; glycerin is a humectant but is not part of it.
Can NMF be washed away?
Yes. Its components are water-soluble, so some is lost with every wash and more when surfactants or hot water are involved. Healthy skin regenerates it over the following hours.
Is the urea in skincare the same urea skin makes?
Chemically, yes — urea is a single small molecule. What differs is concentration: at low percentages it acts mainly as a humectant, and at higher percentages it also softens keratin and loosens scale.
Does everyone produce the same amount of NMF?
No. Levels vary with genetics, age, body site, season and washing habits. Filaggrin variants are common in some populations and reduce production considerably, which is why two people with the same routine can differ markedly in dryness.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
