Hydration measurements of the stratum corneum: comparison between the capacitance method (digital version of the Corneometer CM 825 ® ) and the impedance method (Skicon-200EX ® ) Peter Clarys 1 , Ron Clijsen 2 , Jan Taeymans 3 and Andre ´ O. Barel 1 1 Department of Human Biometry and Biomechanics, Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Brussels, Belgium, 2 University College Physiotherapy Thim van der Laan, Landquart, Switzerland and 3 Berner Fachhochschule, Bern, Switzerland Background: Measurement of stratum corneum (SC) hydra- tion often involves the use of commercial instruments. The aim of this study was to compare and validate two recent instru- ments: the Corneometer 825 ® (digital probe) and the Skicon- 200 EX ® . Methods: In vitro calibration was carried out on filter pads using different solvents, measurements over different layers of plastic foils, and evaluation of desorption kinetics. In vivo mea- surements were carried out on skin sites covering a range of very dry to well-hydrated skin areas. Results: Conductance measurements are influenced by elec- trolytes while capacitance measurements are not. Dielectric constant of the solvents influences the values of both instru- ments (r respectively 0.92 and 0.99). The capacitance method carries information from deeper layers (up to 45 lm) compared with the conductance instrument (up to 15 lm). Desorption experiments show a strong relation between the amount of water and respectively the capacitance and the conductance values. The in vivo experiments revealed a strong relation between the two methods (r = 0.97). Sensitivity of the capaci- tance method is limited for the highest hydration values. Conclusions: Both instruments allow a certain calibration and both give good estimates of the SC hydration. Key words: calibration – capacitance – conductance ª 2011 John Wiley & Sons A/S Accepted for publication 7 July 2011 T HE HYDRATION state of the stratum corneum (SC) is a valuable parameter in different dermato-cosmetic applications. Its determinan- tion is generally based on electrical measure- ments on the skin surface. Most instruments measure either the capacitance or the conduc- tance of the superficial skin layers. Technical aspects such as type of probe surface, direct galvanic contact with the skin or not, distance between the electrodes (mm or lm), and depth of measurement vary when comparing the dif- ferent technologies. The Corneometer CM 825 ® (Courage–Kha- zaka, Cologne, Germany) is based on the capac- itance method. It is a well-known and efficient instrument to measure the hydration of the SC (1–8). The measuring probe of the Corneometer which used an analog signal in the past has been updated to digital technology, resulting in higher stability and less interferences (9, 10). The Skicon instruments (I.B.S. Co., Hamama- tsu, Japan), based on the conductance method are also widely used (11–13). A modern version of the Skicon (Skicon-200EX ® ) has been devel- oped with a new concentric interdigital probe (14). There are several studies comparing the Skicon 100 and 200 with the older versions of the Corneometer (1–8, 11–13). Less data are available describing and comparing the latest model (Skicon-200EX ® ) and the more recent digital version of the Corneometer CM 825 ® (9, 10, 14). The purpose of this work was to compare the in vitro and in vivo performances of the capaci- tance method (analog and digital probes of the Corneometer CM 825 ® ) and the conductance method (Skicon-200EX ® ) on the following aspects: (i) units of measurements, accuracy and calibration, (ii) effect of external factors such as influence of electrolytes, (iii) depth of measure- 1 Skin Research and Technology 2011; 0:1–8 Printed in Singapore Á All rights reserved doi: 10.1111/j.1600-0846.2011.00573.x © 2011 John Wiley & Sons A / S Skin Research and Technology