Electrodermal activity (EDA) is a physiological measurement reflecting the continuous change in the electrical properties of the skin. This measurement is often used by researchers and increasingly by consumer wearable technology to gain insight into a person’s level of psychological or physiological arousal. When the body experiences internal or external stimuli, the skin’s ability to conduct a small electrical current changes, providing an objective index of the body’s real-time response. This metric is valuable in monitoring stress, attention, and emotional engagement because it is largely outside of conscious control.
The Science Behind Electrodermal Activity
The foundation of EDA measurement lies in the activity of eccrine sweat glands, which are highly concentrated on the palms and soles of the feet. These glands are directly controlled by the sympathetic nervous system, the branch of the autonomic nervous system responsible for the “fight or flight” response. When a person experiences an emotionally arousing event, the sympathetic nervous system activates these glands, causing them to secrete a small amount of sweat.
The sweat contains water and electrolytes, and its presence increases the electrical conductivity of the skin. This change is detectable before any visible perspiration occurs, making EDA a sensitive and immediate indicator of sympathetic activation. The eccrine glands measured in EDA primarily respond to psychological and emotional stimuli rather than temperature regulation.
Standard Measurements and Units of EDA
Electrodermal activity is quantified using the standard unit of electrical conductance, the micro-Siemens (\(\mu S\)). The measurement is broken down into two components reflecting different aspects of nervous system function. The first component is the Skin Conductance Level (SCL), or Tonic EDA, which represents the slow-changing, baseline level of skin conductivity. SCL reflects a person’s general state of arousal or alertness over a longer period.
The second component is the Skin Conductance Response (SCR), or Phasic EDA, consists of rapid, short-lived spikes in conductivity. These quick peaks occur in direct response to a specific stimulus, such as a sudden sound or thought. The entire EDA signal combines this constantly fluctuating baseline (SCL) punctuated by these sharp, transient responses (SCRs).
Interpreting the “Good” EDA Score
The concept of a “good” EDA score is highly dependent on context and the individual, as there is no universal optimal number. For Skin Conductance Level (SCL), a healthy range in a relaxed state often falls between approximately 2 and 16 \(\mu S\), though individual baselines vary widely. A stable, moderate SCL during rest is generally considered “good,” indicating a calm but receptive nervous system. Conversely, a consistently high SCL, perhaps over 20 \(\mu S\), suggests chronic stress or hyperarousal.
A truly healthy pattern involves autonomic flexibility, which is best reflected in the Skin Conductance Response (SCR) component. This means the nervous system should be appropriately responsive to stimuli and able to recover quickly afterward. A “good” Phasic EDA involves a clear, measurable spike in response to a stimulus, followed by a fast return to the original baseline. The recovery time measures how efficiently the body can activate and then deactivate its stress response, demonstrating resilience.
Scores indicating a potential issue include an SCL that is too low, suggesting fatigue or a blunted emotional response, or an SCL that is too high, signaling chronic sympathetic activation. For the Phasic response, a healthy individual should show a response latency of about one to three seconds from the stimulus onset. The ability to return quickly to baseline after this peak is often a better indicator of nervous system health than the raw amplitude of the spike itself.
Factors That Influence EDA Readings
A number of non-emotional, physical variables can significantly impact EDA readings, making controlled measurement conditions important for accurate interpretation. Ambient temperature is a major factor, as increased warmth can directly elevate the Tonic EDA (SCL) by triggering sweat glands for thermoregulation. However, the Phasic EDA (SCR) component is generally more robust and less affected by small changes in environmental temperature.
Movement and physical activity are also known to introduce artifacts into the signal, often appearing as sharp, non-emotional spikes in the data. Researchers often place electrodes on the non-dominant hand to minimize movement-related disturbances during tasks. Hydration status and the physical condition of the skin, such as dryness or oiliness, can also affect the baseline conductivity. Certain medications, particularly those with anticholinergic effects, can suppress sweat gland activity and artificially lower EDA scores.