Hydration test: objective measurement of a cosmetic product's moisturizing capacity
The hydration test is the scientific benchmark for quantifying a formula's ability to increase and maintain water levels in the skin's surface layer, the stratum corneum. The instrument used, the corneometer, measures the electrical conductance of the scalp; the higher the conductance, the greater the water content of the stratum corneum. This method, recognized by the Swiss (OCos/OSAV) and European (EC 1223/2009) authorities, provides objective data that is essential for supporting hydration claims.
The protocol begins with the selection of a panel of volunteers representative of the target audience (age, skin type, sensitivity). Each participant receives precise instructions: clean the study area, avoid any competing products for 24 hours, then apply a defined amount of cream or serum to a 2 cm² area. Before application, the corneometer records the baseline value (initial hydration). Immediately after application, a second measurement is taken to assess the instantaneous effect. Additional measurements are taken at 30 minutes, 2 hours, 6 hours, then 24 hours and, if necessary, 48 hours.
Each measurement is compared to a control area left untreated, allowing the hydration gain attributable solely to the product to be calculated. Longitudinal monitoring shows not only the peak hydration level, but also the length of time during which the water level remains higher than in the control area. A product that maintains a gain of at least 15% for 24 hours can legitimately claim «prolonged hydration,» while a gain of 30% at 30 minutes sustained for several hours justifies the claim «immediate moisturizing effect.».
The results are presented in the form of graphs showing variation over time and descriptive statistics (mean, standard deviation). All parameters are recorded in the Product Information File (PIF), ensuring traceability and compliance with regulatory requirements. This robust documentation reassures authorities, distributors, and consumers about the veracity of hydration claims.
By combining the rigor of the corneometer with a realistic application protocol, the hydration test provides reliable scientific evidence, which is essential for positioning a skincare product on the Swiss, European, and UK markets.