Transcutaneous electrical nerve stimulation is a noninvasive pain-relief method whose efficacy depends on several application parameters. Skin-related factors may influence stimulation efficacy. The aim of this study was to determine the influence of selected physicochemical properties of the skin on the perception threshold of electrical stimuli. The superficial sensory threshold was measured on the forearm in 71 female students aged 19-25 years (Fitzpatrick skin phototypes I-III). Skin thickness and density, epidermal thickness, stratum corneum hydration, melanin and hemoglobin content, skin elasticity, and skin reflectance were assessed. Skin thickness, density, and epidermal thickness were not associated with electrical sensory threshold (EST). A higher melanin content in the skin was associated with a higher EST (R = 0.28, p < 0.05). Higher values of the R6 parameter in cutometric measurements were associated with lower sensory EST (R=-0.31, p < 0.01). No other cutometric parameters were associated with EST. Greater reflectance of electromagnetic radiation in the wavelength ranges of 700-1100 nm (R = 0.37, p < 0.01) and 1000-1700 nm (R = 0.37, p < 0.05) was associated with a higher EST. Dermal hydration is the primary determinant of the electrical sensory threshold. High reflectance in the wavelength ranges of 700-1100 nm and 1000-1700 nm indicates low dermal hydration, which reduces electrical conductivity and leads to an increased sensory threshold. A higher sensory threshold was associated with darker skin pigmentation.
Witkoś et al. (Tue,) studied this question.