Information in full and reduced data sets of electrical impedance spectra from various skin conditions, compared...

Information relating to patho-physiological events in living tissues, including skin, should be found in the beta-dispersion frequency range of the electrical impedance. For intact skin, the alpha-dispersion is strongly influenced by the condition of the stratum corneum, particularly its hydration. For intact skin, these dispersions are not well separated: in a Nyquist plot, most of the relatively small beta-dispersion will be hidden behind the upper-frequency end of the alpha-dispersion arc. In the study, information obtained with a set of four indices, claimed to extract most of the information in the pertinent frequency interval, is compared with the full information measured at 31 frequencies, between 1 kHz and 1 MHz, for irritant and allergic contact reactions and nodular basal cell carcinomas, using a holographic neural network that appears to be useful for model-independent evaluation of the consequences of data-reduction procedures. Cole parameters should be avoided in the beta-range for intact skin. The indices are well supported, as long as differences from a reference site are used, and it seems that they can serve as the basis for differential diagnostics even as absolute values, although more information may be extracted from the complete spectrum.