Anne Charpentier Founder & CEO Skinobs
Hydration is the one cosmetic benefit everyone wants, whatever the skin type, the region or the product category. What has changed is the burden of proof. Is a single capacitance reading still enough? Should an eye serum and a lip balm be tested the same way? How do you scientifically demonstrate that hydration lasts? Today, R&D specifications and marketing briefs, from brands and ingredient suppliers alike, call for deeper evidence, longer-lasting effects and real structural benefits. The methodological toolbox has risen to the challenge, with dozens of instruments now able to measure, quantify and visualize hydration from the skin surface down to the dermal matrix. Drawing on Skinobs data, this article explores where the market is heading, revisits the biology behind skin hydration, and shows how to match the right methods to the right claims.
Hydration Testing Goes Deeper
Search activity on the Skinobs platform between January and May 2026 offers a useful window into the industry’s current evidentiary priorities. Over these five months, 480 hydration-related queries were recorded, covering 85 distinct devices from 36 manufacturers and 208 testing providers in 45 countries. On the preclinical side, 19 additional searches targeted specific biomarkers, mainly hyaluronic acid, through proteomic, morphological and histochemical approaches.
The hydration testing market is moving beneath the surface. Brands increasingly favor multilayer evaluation, and infrared spectroscopy, fluorescence imaging, Raman spectroscopy and confocal microscopy are steadily overtaking conventional stratum corneum instruments, which remain in use but no longer set the standard. This shift goes hand in hand with a broader ambition: with the rise of anti-aging and longevity claims, a moisturizer is now expected to strengthen the skin over time. Ultrasound systems, spectrophotometric imaging and confocal microscopy, paired with density and elasticity endpoints, are therefore finding their place at the heart of hydration studies. Yet performance is never assessed in a vacuum. Expectations, consumer profiles and regulatory frameworks vary from one region to another, and a study designed for a European panel cannot simply be transposed to Asia or Latin America. In a testing landscape that is global in scope but concentrated in its expertise, access to reliable international partners running protocols adapted to each market has become a decisive advantage.
Skin Hydration Evaluation: Both Basic and Complex
Skin hydration is not a single parameter, but the result of interconnected mechanisms operating across the different layers of the skin, with varying degrees of complexity and speed. It rests on several structural levels. At the surface, the hydrolipidic film and the resident microbiota maintain the acidic pH required for ceramide synthesis and barrier organization; its disruption triggers a cycle of dryness in sensitive skin. In the stratum corneum, often described as a brick wall cemented by ceramides, fatty acids and cholesterol, this architecture limits transepidermal water loss; its disruption is the hallmark of dry or flaking skin. NMF, derived from filaggrin degradation, retains water within corneocytes but declines with age and frequent washing. In the viable epidermis, aquaporin-3 channels ensure the transport of water and glycerol; their expression decreases with UV exposure and aging, making them a mechanistically relevant criterion in vitro and ex vivo. Finally, the dermal matrix, through hyaluronic acid associated with collagen and elastin, acts as a structural reservoir whose decline after age forty explains the loss of firmness and justifies measurements targeting the dermis.
Three additional dimensions must now be taken into account when designing these studies, and not merely out of academic interest. The first is the exposome, a generic term encompassing UV radiation, particulate matter, ozone and stress. It is known to degrade barrier lipids and accelerate water loss through oxidative and inflammatory mechanisms, and it underlies new categories of claims such as pollution-protective or climate-adapted hydration. The second is peri- and post-menopausal skin, whose distinct physiological profile makes it a specific development axis for hydration claims. Declining estrogen levels simultaneously reduce NMF content, alter lipid organization, decrease dermal hyaluronic acid synthesis and downregulate aquaporin expression, leaving the skin measurably drier and slower to recover. Finally, the skin microbiome, and the biofilm it forms on the skin surface and within its appendages, now constitutes an innovative research field combining classical biometrology with multi-omics methods based on in situ skin sampling.
Choosing the Right Methods
Few measuring devices can simultaneously quantify and visualize a hydrating effect while characterizing the complexity of hydration mechanisms within the skin. This is why evaluation protocols for this claim often begin with in vitro or ex vivo assays to better understand the mechanisms of action of products, ingredients and actives. Results are then validated in vivo, most often using several analytical methods. The era of multimodality is here, and so is the era of agile cross-over between in vitro and in vivo. Skin hydration properties can be evaluated on a variety of substrates: 2D cell lines, iPSC-derived keratinocytes, 3D spheroids or reconstructed skin models, bioprinted or not. On these models, dehydration can be simulated by adding salts or removing the culture medium, and several biomarkers allow the associated biological mechanisms to be tracked. Hyaluronic acid, a key glycosaminoglycan of the extracellular matrix, retains water and interacts with its membrane receptor CD44. Natural moisturizing factor (NMF), derived from filaggrin degradation through caspase-14 activity, maintains skin suppleness and supports desquamation. Aquaporins, channels facilitating water transport across cell membranes, decrease with age and contribute to progressive dehydration. Glycosaminoglycans and ceramides or phospholipids contribute respectively to matrix water retention and to the lipid organization of the stratum corneum, while matrix metalloproteinases (MMPs) regulate the remodeling of the dermal extracellular matrix. These biomarkers are quantified through gene expression, histology, imaging or protein assays (ELISA, Western blot). Overall, the hydrating efficacy of an active ingredient can be reflected in an increased density of the dermal extracellular matrix, a structural network essential for water retention and the biochemical support of skin cells.
Corneometry remains the international reference for immediate surface hydration, valued for its speed and reproducibility, although it probes only the outermost micrometers of the stratum corneum. The measurement is easy, widely recognized, and can be performed in contrasting climates and across diverse ethnic groups. Results are expressed in arbitrary units. The moisturizing effect can be quantified in the short term (30 minutes to 1 hour), over a day (6 to 24 hours) or in the long term (7 to 28 days). Products rich in electrolytes such as salts, small proteins or organic acids increase conductivity and may lead to overestimated hydration values, while formulations high in lipophilic or nonpolar components may lead to underestimated values.
The second recognized method is the indirect measurement of transepidermal water loss (TEWL). Well suited to oily formulations that are difficult to assess with electrical methods, it also provides an overall evaluation of skin barrier function: a reduction in TEWL reflects barrier reinforcement, particularly relevant for sensitive or reactive skin. Based on the diffusion principle, TEWL devices use a sensor-equipped cylinder to measure the humidity gradient between the skin and the top of an open or closed chamber. Subjects must first acclimatize in a room with controlled temperature and humidity.
Impedance spectroscopy extends evaluation to the viable epidermis and dermis, depending on the depth targeted. Infrared and Raman technologies quantify the distribution of water and NMF non-invasively, confocal Raman spectroscopy being the reference method for profiling these components in situ, by depth, without biopsy. Ultrasound and spectrophotometric imaging access the dermis directly to document density and collagen organization, data essential to structural claims. Finally, confocal microscopy, complemented by LC-OCT and multiphoton tomography, offers real-time cellular visualization of the different skin layers.
The choice of method depends on the claim: corneometry for immediate surface hydration, TEWL for barrier repair, impedance for deep hydration, and ultrasound, confocal microscopy or LC-OCT for structural and well-aging claims. But the protocol often matters more than the device: poorly targeted panels, environmental drift or unsuitable measurement time points account for most inconclusive results. It is therefore necessary to precisely define the claim, the population and the measurement time points, with a panel calibrated on baseline corneometry and age, a sample size calculated by a biostatistician, a washout period of one to two weeks and stable laboratory conditions.
Nomadic Diagnostic Tools, a Genuine Trend
Hydration measurement under nomadic conditions, via connected tools and smartphones, has so far relied on the same parameters as in laboratory settings, but could evolve toward more “medical” or “social” criteria, in line with trends driven by influencers. Laboratories will remain the guarantors of objective, large-scale scientific evaluation, while AI, essential to data processing, must remain explainable rather than confined to a black box. Self-assessment questionnaires associated with these diagnostics remain difficult to validate individually, and the management of sensitive skin health data raises major regulatory concerns, with the GDPR providing a strict framework in Europe without equivalent guarantees outside the EU. Captured raw images also often remain the property of application developers. Two development pathways are emerging: the adaptation of spectroscopy to smartphones, and sensors or patches measuring impedance and biomarkers through omics approaches, with CROs playing a key validation role to prevent these tools from remaining mere gadgets.
Conclusion
Designing a hydration study protocol, whether in vitro or in vivo, requires spending sufficient time with CROs to precisely define every parameter: time spent in dialogue is never time wasted. Although hydrating performance is among the fundamental claims of personal care products and its validation may seem straightforward, protocol options are numerous and the range of methods is wide. These choices must be rigorously justified and documented to ensure the scientific soundness and credibility of the results.
