Epidermal hydration of psoriasis plaques and the relation to scaling. Measurement of electrical conductance and transepidermal water loss.

Seventy-seven plaques of ten patients with psoriasis vulgaris were studied with measurement of electrical conductance (3.5 MHz), measurement of transepidermal water loss (TEWL), and clinical scoring of erythema, induration and scaling. Uninvolved skin of the same body region served as control. Findings were very distinct with decreased conductance and increased TEWL. Plaques with no or mild scaling did not differ from grossly scaly plaques. Scales of psoriasis do not seem to exert any major occlusive effect on the water evaporation. The inverse relation between conductance and TEWL indicates reduced water-holding capacity of psoriatic epidermis, being a very common feature.