Effects of topical application of capsaicin to human skin: a comparison of effects evaluated by visual assessment, sensation registration, skin blood flow and cutaneous impedance measurements.

A new non-invasive device, which enables local measurements of electrical impedance, has been used to evaluate the degree of irritation in human skin. The results have been compared with visual scoring, sensations and laser Doppler flowmetry. Capsaicin (50 microliters 1% solution) and control solutions (50 microliters 50% ethanol) were applied in a chamber for 30 min on the volar forearm of 7 volunteers. Values were recorded before application and during the total test period of 4.5 h. Sensations like sting/prick, burn and pain were produced by this treatment, and the flare response was observed. Using the non-invasive laser Doppler flow technique to measure blood flow in human skin, we have shown that topical application of capsaicin abolishes the vasodilator response to local heat provocation (40 degrees C). There was close agreement among values obtained using visual assessments, sensations and laser Doppler flowmetry. Results obtained using electrical impedance measurements were not consistent with the other three methods.