Electrical impedance index in human skin: measurements after occlusion, in 5 anatomical regions and in mild irritant contact dermatitis.

The electrical impedance in 23 healthy volunteers at 2-6 different skin sites was measured with a new impedance device, which makes possible non-invasive local measurements to a controlled depth. In 11 subjects, the test sites were occluded for 24 h using empty Finn Chambers and chambers with water, physiological saline, a paper disc or 0.002% sodium lauryl sulfate (SLS). In the normal skin of 10 subjects, the electrical impedance was measured from 5 different body areas for 5 consecutive days. In 3 subjects, daily measurements for 1 month were done, both from normal skin and from skin following the application of 2% SLS. The results show that the irritation index based on electrical skin impedance gives little day-to-day variation at one and the same test site, in comparison to the variations between different test sites on the same subject and the interindividual variations observed. Significant differences in impedance values between different anatomical regions of normal skin were found. Occlusion does not affect readings taken 24 h or later after removal, but increases variance for readings taken 1 h after removal. Effects on the skin of mild irritation and its recovery phase are easily monitored with the new device. Technology based on electrical impedance, in its newly presented form, with the advantages of improved geometrical definition and depth control, can be used as an objective tool to measure skin irritation. For detection of subclinical irritant contact dermatitis, repeated readings taken over several days may be needed.