Effects of Temperature and Humidity on Skin Resistance, Capacitance, and Threshold Current in Electrotactile Stimulation

Background: Transcutaneous electrical stimulation has been extensively studied and applied due to its numerous advantages. However, individuals exhibit varying skin impedance and threshold current under different ambient temperature and humidity conditions, which prevents the stable operation of electric tactile devices in all environments. Therefore, investigating the variations in threshold current among individuals under different temperature and humidity conditions holds significant value. Methods: A comprehensive experimental system was established based on a skin-electrode impedance model for measuring the electrotactile perception threshold current, skin moisture, resistance, and capacitance under different ambient temperature and humidity conditions. The subjects were classified according to BMI index and gender, and subsequently, the corresponding relationships were statistically analyzed. Results: Results indicate that increases in both localized ambient temperatures and relative humidities can cause an increase in the threshold current, with the magnitude of the increase significantly influenced by gender and BMI. A similar trend was observed for changes in skin surface moisture with temperature and humidity. The findings suggest a strong correlation between changes in skin surface moisture and variations in threshold current, skin resistance, and capacitance under the same conditions. Conclusions: Ambient temperature and humidity obviously affect the threshold current due to changes in skin resistance and capacitance, possibly through variations of the degree of skin hydration. These findings can offer critical quantitative data for the precise operation control of electrical stimulation devices.