What Are Natural Moisturising Factors (NMF) — and How Do They Keep the Stratum Corneum Hydrated?

The small water-binding molecules inside corneocytes that help the outer skin stay hydrated, flexible and functional.

In this guide

• 1. What does NMF actually mean?
• 2. Where is NMF located?
• 3. What is NMF made of?
• 4. How does skin make NMF from filaggrin?
• 5. What does NMF do for the stratum corneum?
• 6. Is NMF the same as the skin barrier?
• 7. NMF vs humectants vs hyaluronic acid vs ceramides
• 8. What can change NMF levels?
• 9. How do scientists measure NMF?
• 10. What does this mean for your routine?
• 11. What this does not mean
• 12. Myths about NMF
• 13. Frequently asked questions

What does NMF actually mean?

Natural Moisturising Factor, usually shortened to NMF, is the collective name for a mixture of small, water-soluble compounds in the stratum corneum - the outermost layer of the epidermis. Many of these molecules are hygroscopic, meaning they interact strongly with water. Their job is not to form an oily seal. Their main contribution is to help corneocytes hold enough water to remain flexible and function normally.

Scientific papers often use the singular phrase “natural moisturizing factor,” even though the mixture contains many compounds. Consumer and product language sometimes says “natural moisturizing factors.” Both usually refer to the same biological pool.

Where is NMF located?

The useful detail is location: classical NMF is concentrated mainly inside corneocytes, the flattened cells of the stratum corneum. The organised lipid matrix - rich in ceramides, cholesterol and free fatty acids - sits primarily between those cells. These two systems work together, but they are not the same thing.

This is why the familiar “bricks and mortar” model needs one extra layer of explanation. Corneocytes are the bricks, extracellular lipids are the mortar, and NMF is part of the water-binding chemistry inside the bricks.

What is NMF made of?

NMF is not one ingredient and it does not have one fixed universal recipe. Classical descriptions include free amino acids and amino-acid derivatives, pyrrolidone carboxylic acid (PCA), urocanic acid (UCA), lactate, urea, inorganic ions/electrolytes, sugars and other small polar compounds.

Older reference tables sometimes assign precise percentages to these groups. Those numbers are useful historically, but they should not be treated as a universal composition for every person, body site or depth of the stratum corneum. Modern analytical work shows site- and depth-related variation.

How does skin make NMF from filaggrin?

A major part of the NMF story begins with profilaggrin, a large protein stored in keratohyalin granules in the granular layer of the epidermis. During terminal differentiation, profilaggrin is processed into filaggrin monomers. Filaggrin first helps organise keratin filaments as cells flatten into corneocytes.

Higher in the stratum corneum, filaggrin is further modified and broken down into free amino acids. Some of those amino acids are converted into derivatives such as PCA and UCA. Classic biochemical studies found that most of the stratum-corneum free amino-acid pool is derived from histidine-rich filaggrin-related protein.

One nuance matters: it is too broad to say that every molecule classed as NMF comes directly from filaggrin. Filaggrin is the dominant source for many amino acids and key derivatives, while lactate, urea, electrolytes and other constituents can have additional origins.

What does NMF do for the stratum corneum?

1. It supports water binding. NMF molecules interact with water and help maintain hydration inside corneocytes. This is especially important because the stratum corneum sits at the dry interface between the body and the environment.
2. It helps keep the outer layer flexible. Adequately hydrated keratin is less brittle and better able to tolerate normal mechanical stress. NMF therefore contributes to the physical “plasticity” of the stratum corneum.
3. It supports orderly desquamation. Enzymes involved in the controlled shedding of corneocytes require an appropriate aqueous environment. Very dry stratum corneum can disturb this process and contribute to visible scaling.
4. It contributes to the chemical environment of the outer skin. Filaggrin-derived acids, including UCA and PCA-related chemistry, are part of the acidic environment of the stratum corneum. However, skin-surface pH is controlled by multiple pathways, so NMF should not be presented as the sole determinant.

Is NMF the same as the skin barrier?

No. NMF is one component of stratum-corneum function, not the entire barrier. A useful separation is: NMF binds water inside corneocytes; intercellular lipids regulate diffusion through the spaces between cells; corneocyte envelopes and cell-cell structures provide mechanical organisation; the acidic surface environment, enzymes and immune/microbial systems add further layers of defence.

That distinction also explains why low hydration and high transepidermal water loss (TEWL) are not interchangeable findings. Hydration measurements ask how much water is present in the stratum corneum. TEWL measures water-vapour flux leaving the skin. One cannot substitute for the other.

NMF vs humectants vs hyaluronic acid vs ceramides

NMF and “humectant” are related but not identical terms. NMF is a biological pool in the stratum corneum. A humectant is a functional description for a material that helps attract or retain water. Many NMF components are humectants; many cosmetic humectants are not classical NMF components.

Hyaluronic acid is a naturally occurring glycosaminoglycan and a widely used topical humectant, but it is not usually included in the classic NMF definition used in older stratum-corneum literature. Ceramides are different again: they are major components of the extracellular lipid matrix, not NMF.

This is why a moisturiser may combine NMF-like materials (for example amino acids, PCA or urea) with glycerin, hyaluronic acid, emollients and occlusives. Those materials can complement each other without being biologically identical.

What can change NMF levels?

NMF varies naturally with body site and depth within the stratum corneum.[5] Filaggrin genetics also matter: human studies have found lower NMF in carriers of loss-of-function FLG variants.

Inflammatory skin disease can alter filaggrin expression and NMF, but NMF measurements are not a self-diagnostic test for eczema or “barrier damage.” Clinical context still matters.

Water exposure can remove water-soluble material from the superficial stratum corneum. Controlled soaking studies show that prolonged soaking, particularly when combined with lipid extraction, can increase NMF loss. That does not mean every normal wash measurably “strips all NMF”; a 2019 Raman study of short-term repeated hand washing found several skin-component changes but no significant NMF change under its tested conditions. The practical message is to avoid making an absolute claim from one cleansing event.

Humidity can influence filaggrin processing and stratum-corneum adaptation, but the biology is regulated rather than a simple “dry air instantly destroys NMF” pathway. Age effects are also not one-directional across human studies, so “NMF always declines with age” is too absolute.

How do scientists measure NMF?

Two common research approaches are tape stripping followed by chemical analysis and in-vivo Raman microspectroscopy. Tape stripping removes very thin layers of stratum corneum that can be analysed by HPLC or related methods for amino acids and derivatives. Confocal Raman spectroscopy estimates NMF non-invasively from molecular spectral signatures at different depths.

These methods can show depth profiles and group differences. They are research measurements, not consumer home tests. A sensation such as tightness, or a photograph of flaky skin, cannot directly tell you the NMF concentration.

What does this mean for your routine?

You do not need to “boost NMF” as a separate daily target. A better goal is to support a hydrated, comfortable stratum corneum through the complete routine.

Use cleansing that removes what needs to be removed without repeatedly pursuing a stripped or squeaky after-feel. Keep bathing and washing conditions reasonable when dryness is a problem. Use a moisturiser whose complete formula fits your skin state and climate; humectants can increase water availability, while emollients and occlusives can improve softness and reduce excessive evaporation.

Products containing amino acids, PCA, urea or lactate can provide NMF-like humectant chemistry on the skin. That is different from proving that the product increases your endogenous filaggrin-derived NMF production. Judge the claim at the finished-formula level.

What this does not mean

• NMF is not an oily film and it is not the same thing as sebum.
• NMF is not the same as ceramides or the extracellular lipid matrix.
• Hyaluronic acid is not a synonym for NMF.
• Low NMF is not something you can diagnose from tightness, flaking or a “pinch test.”
• A product containing NMF-like ingredients is not automatically a complete moisturiser.
• More water exposure is not always more hydrating; prolonged soaking can temporarily change water handling and extract water-soluble components from the superficial stratum corneum.

Myths about NMF

Frequently asked questions

Is NMF one ingredient?

No. NMF is a mixture of small, water-soluble compounds in the stratum corneum, including free amino acids and derivatives, PCA/UCA, lactate, urea, ions and other polar molecules.

Is NMF the same as hyaluronic acid?

No. Hyaluronic acid is an important skin molecule and cosmetic humectant, but it is not the same as the classic NMF pool.

Is NMF part of the skin barrier?

Yes, as one component. NMF supports water binding inside corneocytes, while extracellular lipids and other structures perform different barrier functions.

Can oily skin still have low stratum-corneum hydration?

Yes. Sebum production and stratum-corneum water content are different variables. Oily skin can still feel tight or show lower hydration.

Can cleansing remove NMF?

Water-soluble NMF components can be extracted from superficial stratum corneum, especially with prolonged soaking or repeated stressful exposure. But the effect depends on conditions; one wash does not prove clinically meaningful NMF depletion.

Can skincare replenish NMF?

Skincare can supply NMF-like humectants such as amino acids, PCA, urea or lactate and can improve hydration. That is not automatically the same as increasing the skin’s endogenous filaggrin-derived NMF production.

Does low NMF mean my barrier is damaged?

Not by itself. NMF is one biomarker of stratum-corneum biology. Barrier function also involves lipids, TEWL, hydration, cohesion, inflammation and clinical context.

How is NMF measured?

Research commonly uses confocal Raman microspectroscopy or tape stripping followed by chromatographic analysis such as HPLC. There is no validated consumer home test for NMF.

Does drinking more water directly increase NMF?

There is no simple evidence-based rule that drinking extra water directly raises NMF in otherwise well-hydrated people. NMF production depends on epidermal differentiation and filaggrin processing, not only beverage intake.