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As with other non-invasive techniques, baseline characteristics differ from place to place over the body surface, and age is another important determining factor.

A new, non-invasive device, which enables local measurements of electrical impedance to a controlled depth, has been used to evaluate the degree of irritation in human skin. The results have been compared with those obtained using other non-invasive techniques, i.e. with transepidermal water loss (TEWL), electrical capacitance moist measurement (ECM), laser-Doppler flowmetry (LDF), and visual scoring. Sodium lauryl sulphate solutions (0.1-5.0%), and a blank, were applied in Finn Chambers for 24 h on the volar forearm of 10 healthy volunteers. Values were recorded before application of the test chambers, and at 1 h, 24 h, 1 week and 2 weeks after removal. Thus, both the degree of initial damage and the healing process were monitored. There was close agreement among values obtained using electrical impedance, TEWL and visual readings. Results obtained using ECM and LDF were not consistent with the other three methods. In evaluating irritation of the skin, the practical situation may influence the choice of bioengineering tools. In most circumstances, a combination of methods would be preferable.

Urea has long been used to treat dry skin. In the present report, we compared two creams, identical with the exception that one contained both urea and sodium chloride and the other urea alone, in 22 patients with atopic dermatitis. Following a 2-week wash-out period, their clinically non-eczematous, rough or normal-appearing skin on the forearms was treated twice daily in a double-blind and randomised manner. We examined the treated areas by measuring transepidermal water loss, capacitance and electrical impedance. Our findings suggest that a moisturiser containing both urea and sodium chloride seems somewhat more effective than the same moisturiser without sodium chloride, at least concerning the ability to reverse impedance indices of atopic skin towards normal, an effect ascribed mainly to changes in hydration of the stratum corneum. However, the clinical significance of our impedance measurements is somewhat premature to decide.

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