The skin is an amazing and versatile organ. It’s not only smooth and often nice to look at, but also helps to regulate many functions of the body. It acts as a barrier against environmental threats, contains nerve cells that detect changes such as temperature and pressure, can heal itself, and (ideally) keeps your body at a steady 98.6 degrees.
Yet another great thing about the skin is that it responds to changes, or stimuli, in a way that can be accurately measured via galvanic skin response. The term may sound a little geeky, but we think it’s pretty exciting, especially when we consider the amazing amount of information it can reveal about an individual.
Your skin is electric
Your skin, and much of the rest of your body for that matter, conducts electricity. If your body didn’t conduct electricity, touching a high-voltage fence or sticking a knife in an electric socket would have no effect on you. We wouldn’t be alive without electricity because body functions are controlled by electrical signals.
The skin in particular is a good conductor of electricity, so even a weak electrical signal introduced to the skin can be measured. By applying a constant, unperceived level of voltage to the skin, we can get a baseline reading of the skin’s conductance. Skin conductance (SC) is a term that’s often used interchangeably with electrodermal activity (EDA) or galvanic skin response (GSR).1
A measurable reaction
The baseline reading of skin conductance is referred to as tonic conductance. This conductance level is different for everyone, but it usually ranges from 10 to 50 very small units of conductance called microsiemens. Tonic skin conductance levels also vary based on the person’s psychological state and autonomic regulation at the time the measurement is taken.
While tonic skin conductance is a baseline measurement, phasic conductance changes are the result of the body responding to external stimuli. This increase in conductance compared to the baseline can be observed shortly after a subtle stimulus such as a smell, a sound, an image, or a question is introduced.
Phasic changes can be observed when the skin’s sweat ducts fill in response to a stimulus. After the sweat is deposited or absorbed by the skin, conductance returns to tonic levels. According to Edelberg’s widely accepted sweat circuit model, the extent of this increase can be measured by the amount of sweat and number of sweat glands activated.