Correlation of impedance response patterns to histological findings in irritant skin reactions induced by various surfactants.

We have explored the use of measurements of electrical impedance to discriminate between the effects of different irritant substances upon the skin, and have studied the relationships between impedance and histopathological change. Three compounds with different chemical profiles were tested on volunteers: sodium lauryl sulphate, benzalkonium chloride and nonanoic acid. The concentrations selected were such that each irritant produced responses of a similar order, as judged by visual scores. The magnitude and phase of electrical impedance were measured and, for comparison, also the transepidermal water loss. Four physically distinct aspects (indices) were devised from the impedance data, and the values obtained were statistically analysed. The three irritants produced different effects, giving distinctive impedance patterns. These were also found to be reflected by three different types of histopathological skin response. Our results suggest that the indices can be used to classify irritant contact reactions, which it is difficult or impossible to achieve by other non-invasive techniques.