Electrical impedance and other physical parameters as related to lipid content of human stratum corneum

In previous studies we have shown that variations in the properties of the stratum corneum are reflected by alterations in electrical impedance. The aim of this study was to explore the ability of the electrical impedance technique to detect changes in the lipid content of the stratum corneum, and to compare It with the other non-invasive methods, measurement of transepidermal water loss and of skin moisture.

Twenty-two healthy test subjects were recruited. Transepidermal water loss was measured at standard sites on the forearms and wrists, followed by skin moisture estimation by electrical capacitance, and finally by the recording of electrical impedance spectra in the frequency range 1 kHz to 1 MHz. Readings by all three methods were taken before the start of each series of test procedures, as well as after cyclohexane swabbing, a skin stripping procedure and lipid extraction, and also during the recovery process. A mixture of hexane:isopro-panol was used for lipid extraction of the skin, and the extracts were evaluated using HPLC/LSD and GC/MS/FID analysis. Biopsy samples for light and electron microscopy were obtained after lipid extraction.

Electrical impedance results showed greater changes after lipid extraction than either transepidermal water loss or skin moisture content. Baseline values varied from the cubital fossa to the wrist, both for the non-invasive methods and for lipid composition.

The electrial impedance is dependent on the lipid content of the stratum corneum, as studied by lipid extraction experiments.