Creative Touch Permanent Makeup and Aesthetics

Natural moisturising factor (NMF) is a collection of small, water-soluble, hygroscopic compounds held within the corneocytes of the stratum corneum. Its primary function is to bind water from within the skin cell itself – approximately one third of stratum corneum water is bound to NMF molecules rather than held by the surrounding lipid matrix. NMF is predominantly generated by the enzymatic degradation of filaggrin as corneocytes migrate toward the skin surface, releasing free amino acids and their derivatives including pyrrolidone carboxylic acid (PCA), trans-urocanic acid (UCA), and a broad spectrum of free amino acids. Beyond hydration, PCA and UCA contribute directly to skin surface acidification, supporting the acid mantle on which ceramide-processing enzymes depend. NMF is depleted by surfactant exposure, repeated water contact, inflammation, and filaggrin deficiency – whether genetic or acquired. When NMF is low, the dryness that results does not fully resolve with topical occlusion alone, because the water-binding capacity itself has been lost.

Natural moisturising factor (NMF) is the collective term for a group of small, water-soluble compounds concentrated inside the corneocytes of the stratum corneum. Unlike the extracellular lipid matrix – ceramides, cholesterol, and free fatty acids – which slows water loss by limiting permeability between cells, NMF works from within the cell, binding water molecules and preventing them from leaving the corneocyte even against the osmotic gradient that would otherwise drive them out. Approximately one third of all water present in the stratum corneum is bound to NMF components rather than to keratin or held within the extracellular space. This makes NMF the primary determinant of corneocyte hydration – and corneocyte hydration, in turn, governs the skin’s plasticity, its ability to desquamate normally, and its resistance to mechanical cracking. ^[6]

What NMF Is Made Of

NMF is not a single molecule. It is a mixture of compounds generated through several converging pathways, of which filaggrin degradation is by far the most significant. As corneocytes migrate toward the surface of the stratum corneum, filaggrin undergoes progressive enzymatic proteolysis by caspase-14, calpain-1, and bleomycin hydrolase, releasing its constituent amino acids and metabolic derivatives. These filaggrin-derived products account for 70–100% of the free amino acids present in the stratum corneum and represent the dominant fraction of NMF by volume.

The principal NMF components and their origins are:

Research directly measuring NMF component levels against skin hydration in 196 female volunteers of varied ages found that six specific free amino acids – alanine, arginine, asparagine, glutamine, glycine, and histidine – showed the strongest significant associations with skin hydration values. PCA and UCA, despite being major NMF components by volume, did not show independent hydration correlations in the same analysis, suggesting that the free amino acid fraction is more directly responsible for water binding than commonly appreciated. ^[5]

How NMF Hydrates the Skin

NMF components are intensely hygroscopic: they attract and hold water molecules through hydrogen bonding, drawing moisture from the surrounding environment as well as retaining water already present in the tissue. The water absorption is so efficient that NMF essentially dissolves within the water it has absorbed, forming a gel-like intracellular environment that maintains corneocyte flexibility. Hydrated NMF – particularly the neutral and basic amino acids – forms ionic interactions with keratin fibres within the corneocyte, reducing the intermolecular forces between keratin chains and increasing the stratum corneum’s elasticity and resistance to physical stress.

In vivo confocal Raman microscopy has mapped the depth-dependent relationship between NMF concentration, keratin conformation, and water within the stratum corneum. NMF concentration is highest at the outermost layers (the upper 30% of stratum corneum depth), precisely where keratin is most folded and therefore has fewest available water-binding sites. In these surface layers, NMF effectively compensates for keratin’s reduced hydration capacity – without it, the outermost stratum corneum would lose water-retaining function almost entirely. In the deeper layers, where keratin is more unfolded and has more binding sites, NMF concentration is lower and keratin itself contributes more to water retention. The two systems are therefore complementary and depth-distributed, not redundant. ^[1]

NMF and the Acid Mantle

NMF’s contribution extends beyond hydration. PCA and UCA are among the primary proton donors responsible for the stratum corneum’s acidic surface pH of approximately 4.5–5.5. Research directly measuring PCA’s effect on acid mantle pH and Staphylococcus aureus growth found that PCA shows stronger proton donation ability than UCA at equivalent concentrations – 10mM PCA reduces medium pH to 4.50, compared with 5.48 for UCA – and that both PCA and UCA demonstrated measurable antibacterial activity against S. aureus at clinically relevant concentrations. ^[4]

This acid mantle contribution creates a clinically important feedback loop. The pH 4.5–5.5 environment generated partly by NMF components is the same environment that activates the ceramide-processing enzymes (acidic sphingomyelinase and beta-glucocerebrosidase) responsible for converting ceramide precursors to functional barrier lipids. NMF depletion therefore impairs acid mantle maintenance, which impairs ceramide processing, which weakens the extracellular lipid barrier – meaning that NMF loss has consequences beyond the intracellular hydration deficit it directly creates.

Clinical Pearl The dryness that follows NMF depletion is mechanistically distinct from the dryness caused by lipid barrier disruption. Topical occlusives and ceramide formulations address the lipid barrier gap but do not restore the corneocyte’s internal water-binding capacity. Full recovery requires NMF regeneration – which depends on filaggrin expression, adequate protein availability, and resolution of any inflammatory environment suppressing filaggrin.

What Depletes NMF

Several common exposures reduce NMF, through different mechanisms:

Surfactant exposure is the most well-documented acute depletion route. A controlled patch study using 1% sodium lauryl sulphate ( SLS) demonstrated measurable reduction in most NMF components immediately following 24-hour exposure. Critically, NMF components derived from filaggrin and S-100 protein degradation – primarily the free amino acids and PCA – took the longest to recover, remaining reduced for several days post-exposure, whilst sweat-derived components (urea, lactate) normalised within one day. Full NMF equivalence to untreated skin was reached within 10 days in this controlled study, but this timeline assumes intact filaggrin expression and normal barrier function. ^[2]

Repeated water contact also leaches water-soluble NMF components from the stratum corneum. Because NMF is water-soluble by nature – it must be to function as a humectant – routine bathing gradually depletes it from the upper stratum corneum layers. This is self-limiting in healthy skin with intact filaggrin expression, where ongoing degradation replenishes the supply, but it becomes clinically significant when filaggrin production is compromised. ^[7]

Filaggrin deficiency – whether from FLG loss-of-function mutation or from inflammatory suppression by IL-4 and IL-13 – reduces the supply of NMF precursors at source. Carriers of FLG loss-of-function mutations have measurably reduced PCA and UCA concentrations in tape-stripped stratum corneum compared to wild-type individuals, confirming that NMF levels directly reflect filaggrin status and that NMF components can serve as biomarkers for FLG genotype and barrier compromise. ^[3]

Age-related decline in NMF is an area of active research, with some conflicting findings. The Miyamoto et al. 2024 study in 196 female volunteers found that the relationship between specific NMF components and age varied by component – not all NMF fractions decline uniformly, and the relationship between NMF levels and skin ageing markers is not as straightforward as typically presented in consumer content. The general principle that NMF availability decreases with age is clinically supported, but it is better understood as a downstream consequence of declining filaggrin expression, slower keratinocyte turnover, and reduced total protein availability than as a primary age-related change in its own right. ^[5]

Topical NMF: What Formulations Can and Cannot Do

Topical formulations can supply NMF components directly – PCA, urocanic acid, free amino acids, urea, lactic acid, and glycerol are all used in skincare formulations as humectants. Applied to the skin surface, these compounds provide immediate hygroscopic activity, drawing water into the outer stratum corneum and temporarily improving measured skin hydration. The practical limitation is that water-soluble NMF components applied topically are subject to the same leaching that depletes endogenous NMF – they are washed away, evaporate with water, or are not retained in the corneocyte in the same way that filaggrin-derived NMF is. Topical NMF supply therefore functions as a temporary external support rather than a restoration of the skin’s own water-binding capacity. For clients with chronically low NMF driven by filaggrin deficiency or sustained inflammation, topical humectant application manages the surface presentation without resolving the underlying production deficit.