Next-generation hydration: The science

Hydration has never been a minor cosmetic benefit. Fundamental to normal skin function, adequate hydration helps maintain the processes that keep skin comfortable and functioning effectively. When skin hydration falls, the skin becomes dehydrated, where reduced water content can contribute to tightness, flaking, uneven texture and a dull appearance. Dry skin can also be more prone to irritation, discomfort and visible redness.

Water influences corneocyte flexibility, desquamation, enzyme activity, barrier integrity, the appearance of the skin and ultimately, how comfortable skin feels in the environment it actually occupies.

Yet moisturising has historically been treated as one of formulation’s simpler briefs, reducing a surprisingly complex biological system to attract water with a humectant, slow its escape with an occlusive, demonstrate an increase in capacitance and claim prolonged hydration.

The commercial importance of the category makes that simplicity increasingly difficult to defend. Statista values the global skincare market at approximately US$204 billion in 2026, while McKinsey expects the wider global beauty market to reach US$590 billion by 2030. More significant than market size alone is the direction of consumer expectation.

Hydration remains one of skincare’s most established benefits, but the formulation brief around it is becoming considerably more sophisticated. Consumers are not simply looking for moisturised skin, but for products that support barrier function, perform across different environments and provide evidence proportionate to the claims being made.

For decades, the formulation logic was relatively predictable. Hygroscopic ingredients attracted or retained water within the stratum corneum, emollients improved flexibility and surface feel, and occlusive materials reduced evaporative loss. It works, which is precisely why these principles remain fundamental, but what is changing is our understanding of the system around them.

Skin moisturisation is not only a measure of how much water is present at the surface. It reflects natural moisturising factor (NMF), filaggrin processing, corneocyte maturation and cohesion, intercellular lipid composition and organisation, desquamatory enzyme activity and the movement of water through the epidermis (Verdier-Sévrain and Bonté, 2007).

These processes are interdependent and changes in one alter the performance of another. More research into stratum corneum biology increasingly supports the distinction between just increasing water content and improving the mechanisms that allow skin to manage water effectively.

That distinction gives formulators considerably more room to innovate.

The stratum corneum is the skin’s outermost barrier, but its function is considerably more dynamic than simply being a passive, waterproof layer of the epidermis.

It is a single variable inside an interconnected biological system. Tightly packed dead skin cells, known as corneocytes, sit within an organised extracellular lipid matrix dominated by ceramides, cholesterol and free fatty acids. While, NMF within those corneocytes bind water and help maintain the plasticity required for corneocyte maturation and shedding, also known as desquamation.

This is why water content and barrier function should not be treated as synonyms. Corneometry predominantly estimates hydration within the upper stratum corneum through its dielectric properties, whereas transepidermal water loss (TEWL) assesses water vapour flux from the skin surface. A formulation can increase measured hydration without producing an equivalent improvement in barrier function, just as lower TEWL does not tell us precisely where water is distributed within the tissue (Du Plessis et al., 2013).

For the formulator, the distinction is important because the most credible hydration systems increasingly work across several mechanisms such as attracting and binding water, supporting endogenous water management, maintaining lipid organisation and moderating water loss without compromising sensoriality.

Humectancy remains part of this architecture, but humectants do not behave the same simply because they share an ability to associate with water. Molecular size, hygroscopicity, concentration, interaction with other solutes and polymers and the water activity of the finished system all influence performance.

In the context of the skin, hygroscopic describes a substance’s ability to attract and hold water molecules from its surrounding environment. A highly hygroscopic formulation is not automatically a better moisturiser if the resulting film is tacky, unstable, poorly tolerated or unable to maintain useful water distribution once environmental conditions change.

Glycerin, for example, deserves more scientific respect than being known as an affordable ingredient. It is a highly effective humectant and a naturally occurring, endogenous component of the skin. Aquaporin-3, a specialised cellular channel expressed in epidermal keratinocytes, facilitates the transport of both water and glycerin within the skin, giving this familiar ingredient a role in epidermal hydration physiology beyond simply attracting water at the surface (Fluhr et al., 2008; Hara-Chikuma and Verkman, 2008).

This immediately changes how we formulate for hydration. A moisturiser can have the capabilities to address water acquisition and retention, barrier organisation and water-loss control processes, simultaneously.

Urea, on the other hand, does more than hold water. Research indicates that it can modulate epidermal gene expression, including pathways involved in barrier function and antimicrobial defence. It is transported into keratinocytes through specialised transport mechanisms and has been shown to increase the expression of genes associated with differentiation and lipid synthesis, in turn driving the skin to manufacture more of its own essential lipids and ceramides, preventing TEWL. This helps explain why its function extends beyond passive humectancy (Grether-Beck et al., 2012).

And, NMF-mimetic systems can complement endogenous hygroscopic components by supplying amino acids, PCA and related components involved in stratum-corneum water binding. Where, fermentation-derived polysaccharides can create highly hydrated surface networks and controlled-release systems can alter how quickly hygroscopic materials become available instead of delivering the entire humectant load immediately.

The most interesting innovation is not always found in discovering another molecule, sometimes it is found in formulating a familiar one with greater biological precision.

Hyaluronic acid (HA) demonstrates this particularly well. It is now so established in moisturising products that innovation has frequently become a numbers exercise of several molecular weights, several derivatives and increasingly ambitious hydration language.

There is legitimate science behind molecular-weight differentiation. Raman micro-imaging has demonstrated that HA distribution within skin differs according to molecular size, with lower-molecular-weight fractions penetrating further into the skin than larger polymers, while high-molecular-weight HA is predominantly retained towards the surface, where it contributes film formation and water retention (Essendoubi et al., 2016).

That opens a more sophisticated formulation opportunity.

Different molecular-weight fractions can create different hydration profiles, with larger polymers contributing surface water retention and film properties while carefully selected lower-molecular-weight fractions distribute at different stratum corneum depths. Crosslinked, modified or delivery-supported forms can extend residence time or alter release.

None of this means that combining five forms of HA into one INCI list automatically creates a superior moisturiser. Concentration, polymer interaction, electrolyte tolerance, rheology, film behaviour, tack and the surrounding humectant system determine whether the theoretical advantage survives inside the finished product.

Ceramides face a similar challenge. They are scientifically fashionable because they are biologically important. Together with cholesterol and free fatty acids, ceramides form the highly organised intercellular lipid structures responsible for restricting excessive water evaporation through the stratum corneum (Coderch et al., 2003).

Water retention cannot be separated from the lipid structures regulating its escape. But adding ‘ceramide’ does not automatically recreate a physiological barrier.

Ceramide type, solubilisation, processing temperature, lipid ratio and the organisation formed inside the emulsion matter. Recent work has shown that formulation and incorporation of ceramides influence the barrier-supporting performance expected from the finished product (Schild et al., 2024).

This is where next-generation hydration becomes formulation architecture rather than ingredient decoration. And this is where emulsion science becomes particularly interesting.

Lamellar and liquid-crystalline emulsions can be designed to arrange water and lipids in structures that more closely resemble the lamellar organisation present within the stratum corneum than conventional emulsions designed predominantly around viscosity and appearance. Their effect still depends on the complete formulation, but this architecture can influence hydration, lipid deposition and occlusive behaviour.

The vehicle becomes part of the mechanism. Rather than functioning simply as a carrier for a moisturising active, it can influence lipid deposition, water distribution, release and the behaviour of the film left behind after application.

Occlusion remains one of the most reliable ways to reduce water loss. Petrolatum is exceptionally effective because it creates a highly resistant hydrophobic film across the surface. There is nothing scientifically outdated about that mechanism; its limitation, however, is often sensorial rather than biological.

Particularly in warm climates, a formulation can be technically excellent at preventing TEWL and still fail commercially because the user experiences heaviness, shine, tack, sweat accumulation or poor compatibility with sunscreen and make-up.

The modern challenge is therefore not simply greater occlusion, but controlled water-vapour resistance. Flexible polymeric films, structured lipid phases and skin-affine emollient systems create opportunities for semi-occlusive films that slow excessive water evaporation while retaining acceptable sensory behaviour.

From a formulation perspective, ‘breathable’ can be translated into measurable physical properties such as water-vapour permeability and occlusive behaviour; sufficient resistance to water-vapour transport to reduce excessive TEWL while maintaining acceptable heat, sweat and sensorial behaviour. That is a far more interesting formulation target than simply maximising occlusion.

The balance will differ by product. An overnight balm, facial moisturiser, barrier serum and moisturising SPF do not require identical water-vapour behaviour, even if all four make hydration claims. This is why next-generation hydration should be formulated as a system rather than an ingredient category.

Environmental conditions further complicate that system. A formulation evaluated at approximately 21°C and moderate relative humidity is not experiencing the same thermodynamic conditions as the same product worn outdoors in Dubai, through a Seoul winter, during a humid Bangkok summer or during a global heatwave.

Hot, humid environments introduce a different interaction. Perspiration increases surface water temporarily, while heat can alter TEWL, sebum secretion and perceived greasiness. The presence of water on the surface therefore does not necessarily indicate effective hydration beneath it.

In a study by Kim et al. (2019), hot outdoor exposure increased hydration, sebum secretion, TEWL and greasiness before subsequent sweat evaporation altered hydration again. The skin can therefore have increased surface moisture while simultaneously experiencing increased water loss.

The formulation challenge is not simply atmospheric water. It is perspiration, pollution adhesion, repeated cleansing, high UV load and the user simply not enjoying an unpleasant product with an occlusive film. Consumers can experience surface oiliness and impaired barrier function simultaneously. In arid markets, steeper water gradients can accelerate evaporation, particularly with wind, heat and frequent washing (Engebretsen et al., 2016).

In the Gulf, the defining stress is neither; it is transition. A consumer moves between 45°C outdoors and heavily air-conditioned interiors several times a day. The skin and the product repeatedly encounter changes in temperature, relative humidity, perspiration and evaporation rather than one stable climatic state. The formulation must also survive the journey, not just the climate.

Osmolytes become particularly interesting when hydration is considered through climate. Extremophilic and salt-adapted microorganisms synthesise compatible solutes to maintain cellular water balance and protect macromolecular structures under severe osmotic stress, with some species also increasing their production in response to extreme temperatures (Czech et al., 2018).

Their mechanism differs from conventional humectancy. Osmolytes act partly through preferential exclusion, where they are excluded from the immediate hydration layer surrounding proteins and membranes. This promotes preferential hydration of those structures and modifies local water–water and water–solute interactions, helping stabilise biological structures when environmental conditions become hostile (Yu, Jindo and Nagaoka, 2007; Czech et al., 2018).

For hydration formulation, that mechanism is particularly relevant because osmolytes are also strongly hydrated themselves and have demonstrated prolonged moisturising and barrier-supporting effects following topical application (Graf et al., 2008).

Rather than simply attracting water at the surface, compatible osmolytes offer a way of thinking about hydration as protection of the local water environment around biological structures. In climates characterised by heat, low humidity or repeated movement between outdoor heat and air-conditioned interiors, this creates an interesting route for climate-adaptive hydration.

Domestic water quality adds another variable. Hard water should not simply be described as dehydrating, but research has shown that washing with harder water can increase surfactant deposition on the skin and has been associated experimentally with increased TEWL and irritation (Danby et al., 2018).

For formulators, this makes cleanser mildness, surfactant deposition and the hydration system used after cleansing particularly relevant in regions where water hardness varies considerably.

This changes the formulation brief. A climate-adaptive moisturiser needs to consider humectant water activity, evaporation rate, film flexibility, sweat compatibility, sebum interaction, lipid deposition, dry-down, SPF layering and stability after repeated heat cycling. ‘Lightweight moisturiser for summer’ suddenly sounds rather unsophisticated.

More sophisticated formulation requires equally sophisticated substantiation.

Corneometry remains an established method for assessing changes in stratum-corneum hydration, but formulation composition can influence the measurement itself. Electrolytes, product residue, anatomical site and ambient conditions affect electrical methods, which means a higher reading does not automatically describe a deeper or more durable biological change (Berardesca, 1997; Du Plessis et al., 2013).

TEWL answers a different question of how readily water is moving through and away from the barrier. The most compelling studies therefore increasingly combine methods. Confocal Raman spectroscopy can resolve water and molecular concentration profiles through depth, helping distinguish transient surface hydration from changes in vertical distribution (Caspers et al., 2001).

Lipid analysis can determine whether a barrier-support formulation genuinely changes ceramide or fatty-acid composition. Tape stripping can examine NMF and biochemical markers, while imaging and established electrical measurements can provide complementary structural and functional endpoints.

The value lies not in producing the longest possible clinical report, but in selecting the measurement that corresponds to the mechanism. A 48-hour hydration claim requires evidence at 48 hours. A barrier claim requires an appropriate measure of barrier function, while a claim to restore skin lipids requires evidence that the relevant lipids changed.

Otherwise, we are measuring what is convenient rather than what we are claiming.

Within the EU, cosmetic claims must comply with Commission Regulation (EU) No 655/2013. For hydration claims, the important distinction is between cosmetic and medicinal positioning.

Claims such as ‘hydrates for 48 hours’, ‘supports the skin barrier’ or ‘helps reduce transepidermal water loss’ must be supported by appropriate evidence, while language such as ‘treats eczema’, ‘heals damaged skin’ or unqualified biological ‘repair’ can move a product towards medicinal positioning and should be avoided unless the product is regulated accordingly.

The more mechanistic the claim, the more precisely the finished formulation must substantiate it.

Hydration innovation is moving away from simply increasing the number of water-binding ingredients in a formulation and towards the controlled management of water across a biological interface.

That means understanding molecular size and distribution rather than using multiple molecular weights for label theatre. It means considering ceramides as part of an organised lipid system rather than a solitary active. Engineering emulsion structure and film permeability alongside humectancy, and testing whether that architecture remains sensorially acceptable when exposed to sweat, heat, low humidity, air conditioning and the other products applied around it.

Most importantly, it means recognising that hydration is not one measurement and not one mechanism. The next generation will be defined by coherence between skin biology, water behaviour, formulation architecture, climate and the evidence used to substantiate performance.

References

• Berardesca, E. (1997) ‘EEMCO guidance for the assessment of stratum corneum hydration: electrical methods’, Skin Research and Technology, 3(2), pp. 126–132.
• Caspers, P.J., Lucassen, G.W., Carter, E.A., Bruining, H.A. and Puppels, G.J. (2001) ‘In vivo confocal Raman microspectroscopy of the skin: non-invasive determination of molecular concentration profiles’, Journal of Investigative Dermatology, 116(3), pp. 434–442.
• Coderch, L. et al. (2003) ‘Ceramides and skin function’, American Journal of Clinical Dermatology, 4(2), pp. 107–129.
• Czech, L. et al. (2018) ‘Role of the extremolytes ectoine and hydroxyectoine as stress protectants and nutrients: genetics, phylogenomics, biochemistry, and structural analysis’, Genes, 9(4), 177.
• Danby, S.G., Brown, K., Wigley, A.M., Chittock, J., Pyae, P.K., Flohr, C. and Cork, M.J. (2018) ‘The effect of water hardness on surfactant deposition after washing and subsequent skin irritation in atopic dermatitis patients and healthy control subjects’, Journal of Investigative Dermatology, 138(1), pp. 68–77.
• Du Plessis, J. et al. (2013) ‘International guidelines for the in vivo assessment of skin properties in non-clinical settings: Part 2. Transepidermal water loss and skin hydration’, Skin Research and Technology, 19(3), pp. 265–278.
• Engebretsen, K.A. et al. (2016) ‘The effect of environmental humidity and temperature on skin barrier function and dermatitis’, Journal of the European Academy of Dermatology and Venereology, 30(2), pp. 223–249.
• Essendoubi, M. et al. (2016) ‘Human skin penetration of hyaluronic acid of different molecular weights as probed by Raman spectroscopy’, Skin Research and Technology, 22(1), pp. 55–62.
• European Union (2013) Commission Regulation (EU) No 655/2013 of 10 July 2013 laying down common criteria for the justification of claims used in relation to cosmetic products, Official Journal of the European Union, L190, pp. 31–34.
• Fluhr, J.W., Darlenski, R. and Surber, C. (2008) ‘Glycerol and the skin: holistic approach to its origin and functions’, British Journal of Dermatology, 159(1), pp. 23–34.
• Graf, R. et al. (2008) ‘The multifunctional role of ectoine as a natural cell protectant’, Clinics in Dermatology, 26(4), pp. 326–333.
• Grether-Beck, S. et al. (2012) ‘Urea uptake enhances barrier function and antimicrobial defence in humans by regulating epidermal gene expression’, Journal of Investigative Dermatology, 132(6), pp. 1561–1572.
• Hara-Chikuma, M. and Verkman, A.S. (2008) ‘Roles of aquaporin-3 in the epidermis’, Journal of Investigative Dermatology, 128(9), pp. 2145–2151.
• Kim, S. et al. (2019) ‘Influence of exposure to summer environments on skin properties’, Journal of the European Academy of Dermatology and Venereology.
• McKinsey & Company (2025) A close look at the global beauty industry in 2025.
• Schild, J. et al. (2024) ‘The role of ceramides in skin barrier function and the importance of their correct formulation for skincare applications’, International Journal of Cosmetic Science, 46(4), pp. 526–543.
• Statista (2026) Skin Care – Worldwide Market Forecast.
• Verdier-Sévrain, S. and Bonté, F. (2007) ‘Skin hydration: a review on its molecular mechanisms’, Journal of Cosmetic Dermatology, 6(2), pp. 75–82.
• Yu, I., Jindo, Y. and Nagaoka, M. (2007) ‘Microscopic understanding of preferential exclusion of compatible solute ectoine: direct interaction and hydration alteration’, Journal of Physical Chemistry B, 111(34), pp. 10231–10238.

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