Measuring depth depends on frequency in electrical skin impedance measurements

Backgroundaims: Multi-frequency electrical measurements in vivo on stratum corneum are frequently reported in the literature. It is well known that the measured volume of skin is dependent on measuring frequency, and we wanted to investigate to what extent viable skin influences the measured impedance as a function of frequency. Methods: Finite element modelling (FEM) was used to investigate the current and potential distribution in the skin when measuring impedance with two concentric surface electrodes. Results: The study showed that the impedance measured reflects mainly the stratum corneum at low frequencies, in this case below 1 kHz, and that the viable skin dominates at higher frequencies. Conclusion: It is concluded that a multi-frequency measurement on isolated stratum corneum is not possible in vivo with conventional techniques, except within a very narrow and low frequency range.