Human eccrine sweat glands, present on the palmar surfaces of the hands and bottoms of the feet, are innervated by the sympathetic branch of the autonomic nervous system (ANS). These glands respond readily to a person’s mental and emotional state are are often more responsive than other variables such as skin temperature.
The human eccrine glands act as variable resistors. When the eccrine glands fill with fluid, the skin resistance decreases and the conductance increase. Consequently, it is possible to measure skin conductance by placing two electrodes on the fingers of human subjects. The measured parameter, know as skin conductance, is expressed in microsiemens (µS). Microsiemens are a common unit of conductance.