Electrodermal activity (EDA) captures changes in the electrical properties of the skin. An EDA scan, historically known as a galvanic skin response (GSR) test, monitors the skin’s ability to conduct a small electrical current. This measurement serves as a direct indicator of physiological arousal, reflecting the intensity of a person’s emotional or cognitive state. Tracking these subtle electrical shifts, an EDA scan offers objective, continuous data about the body’s real-time response to stimuli.
The Science Behind Skin Conductance
The mechanism underpinning electrodermal activity is linked to the sympathetic nervous system, which governs the involuntary “fight or flight” response. This branch of the autonomic nervous system is the sole driver of the EDA signal, making it a pure index of sympathetic arousal. When a person experiences emotional or cognitive activation, the sympathetic nervous system signals the eccrine sweat glands to become active.
These eccrine glands are densely concentrated on the palms of the hands and the soles of the feet, which are the primary sites for EDA measurement. The activation causes the glands to fill with sweat, which is mainly water and electrolytes. Since water and salt are good electrical conductors, the presence of this moisture within the skin’s stratum corneum layer significantly increases the skin’s electrical conductivity.
This process momentarily lowers the electrical resistance of the skin, allowing an applied current to pass through more easily. The electrical change is not related to thermoregulation, but rather a byproduct of emotional or mental activity. Therefore, the measurement of skin conductance acts as a window into the dynamic, moment-to-moment changes in sympathetic nervous system output.
How EDA Scans Are Measured
An EDA scan is performed using a specialized device that includes two electrodes placed on the skin, typically on the fingers or the palm of the hand. These electrodes apply a constant, very small electrical voltage that is imperceptible to the person being tested. The device then measures how easily the current passes between the two electrode sites.
The resulting measurement is expressed in microsiemens (uS), the standard unit of electrical conductance. The data collected consists of two main components: tonic and phasic activity. Tonic electrodermal activity, or Skin Conductance Level (SCL), represents the slower, baseline level of arousal over a longer period, such as a person’s general relaxation or stress level.
Phasic electrodermal activity, known as the Skin Conductance Response (SCR), captures the rapid, transient spikes in conductance that occur in direct response to a specific stimulus, like a sudden noise or a presented image. Modern technology has incorporated miniaturized EDA sensors into wearable devices, such as smartwatches and fitness trackers. These wearables use the same principle of contact electrodes to provide continuous, real-time monitoring of sympathetic activity during daily life and sleep.
Common Uses of Electrodermal Activity
EDA’s ability to objectively quantify physiological arousal has made it a valuable tool across scientific and commercial applications. In clinical and psychological research, EDA is frequently used to measure emotional regulation, anxiety, and stress levels. Researchers observe skin conductance responses to specific stimuli to better understand the psychophysiological markers of conditions like phobias or generalized anxiety disorder.
Wearable technology utilizes EDA to track stress and monitor sleep quality in consumer health and wellness. By detecting elevated skin conductance levels throughout the day and night, these devices offer users an objective metric for their autonomic nervous system activity. This data can inform biofeedback programs, which teach individuals techniques to consciously manage their physiological responses to stress.
Historically, electrodermal activity has been employed in forensic and investigative settings, most notably in polygraph testing. While the polygraph measures multiple physiological signals, the EDA component tracks heightened arousal during questioning. It is important to note that the polygraph measures the intensity of arousal or emotional salience, not whether a person is being truthful or deceptive.
Understanding Your EDA Results
Interpreting the data from an EDA scan involves analyzing the magnitude and frequency of the skin conductance measurements. Generally, a higher skin conductance level or a greater number of skin conductance responses indicates a state of higher physiological arousal. This elevated activity suggests the sympathetic nervous system is highly engaged, which can be linked to focused attention, excitement, or feelings of anxiety and stress.
Conversely, a lower skin conductance level and infrequent, smaller responses typically suggest a state of deep relaxation, calm, or sleep. The absolute EDA measurement itself does not reveal the specific emotion a person is experiencing. Since both positive emotions (like joy) and negative emotions (like fear) cause an increase in arousal, EDA measures the intensity of the emotional response, not the quality.
For accurate interpretation, EDA results must be considered within the context of established baselines and the specific situation a person is in. An individual’s baseline SCL, or tonic activity, can vary significantly, meaning a high reading for one person might be normal for another. Understanding these individual differences and the circumstances of data collection is essential for drawing meaningful conclusions.