What Does Skin Conductance Level Measure?

Skin conductance level measures the electrical properties of the skin, offering a window into the body’s psychological and physiological states. This measurement is part of a broader category known as electrodermal activity (EDA), which tracks how the skin’s electrical characteristics change in response to stimuli. Because these changes are tied to subconscious processes, they provide an objective way to track shifts in a person’s internal state. This information is used across many scientific fields to explore human behavior.

The Physiological Basis of Skin Conductance

Changes in skin conductance are directly linked to the activity of the eccrine sweat glands. These glands are distributed across the body but are most concentrated in areas like the palms of the hands and the soles of the feet. The primary function of these glands is to regulate body temperature through perspiration. They are also activated by psychological or emotional stimuli, a process controlled by the sympathetic nervous system (SNS), which governs the body’s “fight-or-flight” responses and arousal levels.

When the sympathetic nervous system becomes more active, it signals the eccrine glands to secrete sweat. This sweat is an electrolyte solution containing electrically charged ions. As the sweat ducts fill, they create a more conductive pathway for electricity. The more sweat present on the skin’s surface, the more easily the skin conducts electricity, linking nervous system arousal to a measurable electrical property.

Understanding Skin Conductance Level

The signal of electrodermal activity is composed of two main parts, and Skin Conductance Level (SCL) is one. SCL represents the tonic component, which is the slow-moving, background level of skin conductance. This measure captures the baseline state of arousal over longer periods, ranging from seconds to minutes. It reflects a person’s general physiological condition rather than a reaction to a specific, momentary event.

SCL must be distinguished from the other component of EDA, the Skin Conductance Response (SCR). SCRs are phasic, meaning they are rapid, short-lived peaks in conductance that occur in direct reaction to a stimulus, such as a sudden noise. These responses are superimposed on the slower-drifting SCL. While an SCR indicates a brief reaction, the SCL provides the context by showing the underlying level of arousal from which that reaction emerged.

How Skin Conductance Level is Measured

Measuring skin conductance level is a non-invasive process where a device passes a small, imperceptible electrical current through the skin. This is accomplished by placing at least two electrodes on the skin’s surface. These electrodes are placed on the fingers, palms, or soles of the feet, where the high density of eccrine sweat glands makes the signal reliable. The measurement device, an EDA meter, records how easily the current travels between the electrodes.

The most common electrodes used are made of a silver/silver-chloride (Ag/AgCl) compound for stable readings. The data collected reflects the skin’s conductance, which is the reciprocal of resistance, and is reported in units called microsiemens (µS). A normal resting range for SCL is between 2 and 16 µS, although this varies significantly between individuals.

Interpreting Skin Conductance Level

An increase in skin conductance level is interpreted as a sign of heightened sympathetic nervous system arousal. This arousal is not specific to any single emotion; it can be triggered by states like stress, excitement, anxiety, fear, or intense focus. For example, a person engaged in a demanding cognitive task would likely show an elevated SCL. The measurement reflects the intensity of the physiological state but does not reveal the specific emotion behind it.

Conversely, a decrease in SCL points to a reduction in arousal, such as a state of relaxation or calmness. SCL is influenced by individual differences, as some people have more variable signals than others. External factors, like room temperature, can also affect the measurement by altering sweat levels independently of psychological state.

Applications of Skin Conductance Level

SCL’s ability to track subconscious arousal makes it a valuable tool in many fields. In psychology research, it is used to study emotional responses, cognitive effort, and attention. Researchers might monitor SCL to gauge how individuals react to stimuli or to understand the cognitive load associated with complex tasks. This provides objective data that can complement self-report measures.

Beyond academic research, SCL has practical applications in clinical settings for biofeedback therapy to manage anxiety and stress. By seeing their SCL in real-time, individuals can learn to consciously influence their arousal levels. In human factors and ergonomics, SCL helps assess the mental workload of operators performing tasks like driving. Neuromarketing also uses these measurements to gauge consumer engagement with advertisements and products.