Dermatological applications of skin potential level measurements.

Decreasing of the negativity of skin potential level (SPL) on the palmar surface of healthy subjects associated with the process of falling asleep, with a return to increased negativity on awakening, was reported by Nishimura and Nagumo (Ergonomics 1985;28(6):905-913). To clarify the dermatological significance of SPL measurements, the SPL of normal skin at various paired sites in the right upper limb, right lower limb and trunk in healthy volunteers and also at the sites of lesions in patients with psoriasis, herpes zoster and nummular eczema were measured. Fitting curves for the decreasing showed exponential characteristics on the palm and the heel where many sweat glands are involved. SPL differences on other sites did not show the exponential decreasing, but kept almost constant values. The values are negative on normal skin, but positive on lesions sites. We also studied the effects of water content in the horny layer on SPL differences and the biorhythmical changes of SPL differences. We discussed the reasons why these results were obtained. The present study provides the promise of an objective, noninvasive and easy method of testing dermatological conditions.