Mild and below threshold skin responses to sodium lauryl sulphate assessed by depth controlled electrical impedance

There is a need for objective and noninvasive methods to quantify and classify weak reactions in the skin. We have explored the capacity of the electrical impedance technique to evaluate mild irritant skin reactions and responses below the clinical threshold by using low concentrations of sodium lauryl sulphate.

Twenty-one healthy subjects were patch tested with 0.004, 0.02, 0.1 and 0.5% sodium lauryl sulphate on both volar forearms. An unoccluded area was used as a reference site. Values were recorded before application and 24 h after removal of the chambers. The magnitude and phase of electrical impedance were measured in the frequency range 1 kHz to 1 MHz at five depth settings. Four indices were devised from the impedance data, and the values obtained were statistically analysed.

Between day 1 and day 3, statistically significant differences were found from the concentration of 0.02%, and the significance level increased from depth 1 to depth 5.

Our results confirm that the electrical impedance method is a sensitive technique for detection of macroscopically negative responses induced by sodium lauryl sulphate, and that depth selection can be used to optimise the signal-to-noise ratio.