Background/aims: The hydration state of stratum corneum can be measured with different instruments. In the present study, five instruments were compared under different experimental in vitro conditions: Corneometer CM 820 and CM 825, Skicon 200, Nova DPM and DermaLab. Methods: A sorption‐desorption test, measurements on different filters and with liquids with different dielectric constants, measurement‐depth analysis and measurements on different agar plates were performed. Results: Good correlation between the values of the five instruments and μl (sorption test: varying from r= 0.8249 to r= 0.9635) and time (desorption test: correlation varying from r= 0.7615 to r=0.9909) could be demonstrated. A high Spearman correlation coefficient (r) could be proven for dielectric constant (dc)/CM 820 (r=0.9333), dc/CM 825 (r=0.9833) and dc/Nova DPM (r=0.9048). A lower correlation or no correlation was found for dc/DermaLab (r=0.8469; P=0.023) and dc/Skicon 200 (r=0.9000; P=0.083). Conclusions: For each of the five instruments, the electrical field of measurement can be assumed to cover the following depths: CM 820, between 30 and 45 μm; CM 825, around or less than 15 μm; Skicon 200, less than 15 μm; Nova DPM, between 45 and 60 μm; DermaLab, around or less than 15 nm.

Different irritation patterns need different measurement modalities in order to give optimal discrimination over time.