Hydration is one of the most established, yet still one of the most strategically important, performance territories in skincare. Consumers immediately understand the promise of hydrated skin, but for brands, formulators and claim specialists, substantiating this benefit requires much more than showing a temporary increase in water content. Today, hydration evaluation has to connect several dimensions: the biological mechanism of action, the measurable effect on skin, the barrier function, the visible skin appearance, the sensory perception and, ultimately, the consumer experience.
This is why a robust hydration protocol should be designed as a multi-tool strategy rather than as a single instrumental measurement. The first question is not only “does the product increase hydration?”, but also “how does it contribute to skin hydration and how can this effect be demonstrated in a relevant, reproducible and claim-oriented way?”.
At Mérieux NutriSciences | Pharma & HealthCare, CosmeticLAB approaches hydration and nourishing claims by combining complementary methods, selected according to the product positioning, the expected mechanism of action and the final communication objective.
In vitro testing can help investigate the mechanism behind the performance. For example, the evaluation of Aquaporin 3, a membrane channel involved in water and glycerol transport, may be used to explore how an ingredient or finished formula supports the biological pathways associated with skin hydration. This mechanistic layer is particularly valuable when brands want to go beyond a generic moisturising claim and build a more science-based narrative around the product.
In parallel, in vivo measurements on volunteers remain essential to provide direct evidence of product performance under real conditions of use. The evaluation of stratum corneum water content, using instruments such as Corneometer or Moistumeter, is a key parameter to quantify the hydration effect at the skin surface. However, water content alone does not fully describe the quality of skin hydration. A formula may increase the water level temporarily without improving the skin’s ability to retain it. For this reason, trans-epidermal water loss, measured through TEWL, is an important complementary endpoint to assess the skin barrier and water loss. When hydration is interpreted together with barrier function, the result is a more complete picture of product efficacy.
Hydration is also closely linked to the physical properties of the skin. Well-hydrated skin is often perceived as more comfortable, smoother and more supple. Instrumental evaluation of skin viscoelasticity, using devices such as Cutometer or Elastimeter, can therefore complement hydration measurements by assessing parameters related to firmness, elasticity and laxity. This is particularly relevant for products positioned at the intersection between hydration, nourishing, well-ageing and skin comfort.
A further layer of evidence can be provided by 3D imaging and skin profilometry, which help document how hydration may translate into visible and measurable changes in skin appearance. Parameters such as micro-roughness, desquamation, skin texture and smoothness are highly relevant because they connect the biological and instrumental assessment with what consumers can actually see and feel. In this perspective, imaging is not only a visual support for communication, but also a technical tool to monitor the evolution of the skin surface before and after treatment.
Clinical evidence also plays a central role. Dermatological scoring, performed at defined time points, can support the interpretation of instrumental data by assessing the skin condition from a clinical perspective. This is especially valuable when hydration claims are associated with sensitive skin, dryness, tightness, roughness, flaking or discomfort. By combining instrumental measurements with clinical observation, the study can better capture both objective performance and the visible improvement of the skin.
Depending on the claim territory, hydration protocols may also be enriched with additional endpoints. When the formula targets sensitive or stressed skin, the evaluation of barrier response after mechanical insult and the dosage of inflammatory mediators such as IL-1α can help document a soothing or protective effect. When the product is intended for face, body, neck or décolleté, the protocol can be adapted to the specific application area, taking into account skin physiology, consumer expectations and usage conditions.
The strength of an integrated testing strategy lies in the ability to correlate different types of evidence. Instrumental measurements provide objective data; dermatological scoring and expert evaluation add clinical relevance; imaging can generate visual and quantitative support; clinical scoring and expert evaluation add dermatological observation; imaging can generate visual support; sensory and consumer science help understand how the product is perceived during and after application. This is particularly important because hydration is not only a biological parameter. It is also a sensorial experience: freshness, comfort, softness, reduced tightness, smoother skin and a pleasant after-feel all contribute to the way consumers recognise and value a moisturising product.
For brands, the challenge is therefore to transform technical data into meaningful, responsible and substantiated claims. A well-designed hydration study should start from the desired claim architecture and then translate it into a coherent protocol: mechanism of action, short-term and/or long-term performance, barrier support, skin appearance, clinical evidence, skin feel and consumer perception. The most relevant studies are those built around the product’s real promise, not around a standard list of tests.
As skincare continues to evolve toward more sophisticated, evidence-based and experience-driven products, hydration evaluation must evolve as well. The future of moisturising claims will not be based only on measuring water in the stratum corneum, but on demonstrating how a product supports the skin as a living, responsive and sensorial organ. In this context, combining in vitro, in vivo, instrumental, imaging and sensory approaches is not an additional complexity: it is the key to building credible, differentiated and consumer-relevant evidence.
CONTACT
Chiara Chiaratti
Cosmetics and Personal Care Project Manager
