Electrodermal Activity (EDA) is a non-invasive method for measuring continuous changes in the electrical properties of a person’s skin. This measurement reflects the body’s physiological arousal, providing an objective window into internal state changes. EDA is often used in research and monitoring contexts to quantify subconscious responses to various stimuli. This technique is also widely known as Galvanic Skin Response (GSR).
The Core Mechanism of Electrodermal Activity
The physical changes measured by EDA are directly controlled by the sympathetic branch of the autonomic nervous system. This system is responsible for involuntary functions and governs the body’s “fight-or-flight” response to perceived challenges. An increase in psychological or emotional arousal triggers this system into action.
Sympathetic activation stimulates the eccrine sweat glands, which are primarily concentrated on the palms of the hands and the soles of the feet. These glands are almost exclusively regulated by the sympathetic nervous system. When the glands begin to secrete tiny amounts of sweat, the skin’s electrical conductivity changes.
Sweat is composed mainly of water and electrolytes, which act as electrical conductors. As sweat glands become active and fill with this conductive solution, the skin’s overall electrical resistance decreases, meaning its conductance increases. The device detects this slight increase in skin conductance as a measure of inner excitement or cognitive demand.
How the Measurement Device Works
To capture this biological activity, the device uses two electrodes, or sensors, typically placed on the fingers or the palm of the hand. These electrodes are often made from silver-chloride and are highly sensitive to the skin’s ionic changes. The device applies a small, constant, and imperceptible electrical voltage across the two electrode points.
The current that flows between the electrodes is measured, providing a measure of skin conductance. This measurement is expressed in microsiemens, which is the standard unit for electrical conductance. A typical range for human skin conductance falls between one and twenty microsiemens.
The device continuously monitors this measurement over time, recording subtle fluctuations in the current flow. An increase in the microsiemens reading signifies a decrease in skin resistance, indicating a rise in sympathetic nervous system activity. This recorded data reflects real-time, moment-to-moment changes in physiological arousal.
Common Applications of EDA Monitoring
EDA monitoring has widespread utility across various fields due to its objectivity as a measure of physiological arousal. In psychological research, it is frequently used to study emotional processing, attention, and cognitive load. Researchers pair specific stimuli with the resulting EDA changes to understand how people react subconsciously.
Clinically, EDA serves as a component of biofeedback training, assisting individuals with anxiety and stress management. Patients observe their physiological state, represented by the EDA signal, and practice relaxation techniques to consciously lower arousal levels. This technique helps them gain voluntary control over involuntary nervous system responses.
The technology has moved into consumer health, with many smartwatches and fitness trackers now incorporating EDA sensors. These devices track a user’s skin conductance throughout the day, providing an index of their overall stress level. EDA measurement also remains one of the physiological variables recorded in forensic applications, such as polygraph testing.
Interpreting the Results
An EDA signal is composed of two distinct components: tonic and phasic activity. Tonic activity, or the Skin Conductance Level (SCL), represents the slower, underlying baseline of skin conductance that changes over minutes. This baseline reflects a person’s general state of alertness, overall stress level, and environmental factors.
Phasic activity, known as the Skin Conductance Response (SCR), consists of rapid, short-lived spikes in conductance that occur within seconds. These swift changes are the body’s direct response to a specific, identifiable stimulus, such as a surprising sound or an emotionally charged image. The amplitude of these phasic responses indicates the intensity of the body’s reaction.
EDA measures the intensity of arousal, but it cannot reliably distinguish between different types of emotion. For example, a high-amplitude spike could be triggered by fear or excitement, as both are states of high arousal. Therefore, responsible interpretation of EDA data requires combining it with other measures, such as heart rate, facial expressions, or situational context.