Skin conductance (SC) measures the skin’s ability to conduct a small electrical current. This measurement reflects changes in the skin’s moisture level, which is closely tied to psychological and physiological arousal. SC is a common tool for objectively assessing a person’s level of engagement or stress. It functions as a reliable, involuntary indicator of how activated an individual’s system is in response to their environment or internal thoughts.
The Biological Basis of Skin Conductance
The mechanism behind skin conductance is rooted in the body’s involuntary preparation for action. This process is managed by the sympathetic branch of the autonomic nervous system, which prepares the body for “fight or flight” responses. Since eccrine sweat glands lack parasympathetic innervation, skin conductance reflects activity only within the sympathetic nervous system.
The change in electrical conductivity is directly linked to the activity of eccrine sweat glands, the primary sweat glands in the human body. These glands are highly concentrated on the palms of the hands and soles of the feet. When the sympathetic nervous system is activated, it signals these glands to produce minute amounts of sweat.
Sweat is an electrolyte solution containing water and salts, which significantly increases the skin’s electrical conductivity. The moistening of the skin surface by this secretion lowers the skin’s electrical resistance. This involuntary physiological response is registered as an increase in skin conductance, providing a quantifiable measure of sympathetic activation.
Triggers for Changes in Skin Conductance
Changes in skin conductance are triggered by any stimulus that causes an increase in sympathetic nervous system activity, reflecting a state of general activation. This includes psychological arousal, which can stem from intense emotions like fear, excitement, anxiety, or strong positive feelings. While SC measures arousal, a core dimension of emotional response, it cannot differentiate between specific emotions like happiness or fear on its own.
Cognitive processes serve as potent triggers, with tasks requiring high attention or mental workload leading to measurable increases in conductance. Solving complex problems or focusing intently on a task can cause the signal to rise as the brain demands more physiological resources. Internal stimuli, such as simply holding one’s breath or engaging in exciting or embarrassing thoughts, can provoke a response.
Environmental and external factors, such as a sudden loud noise, a startling event, or even temperature changes, can activate the response. While eccrine glands primarily function in thermoregulation, the palms and soles are particularly sensitive to emotional stress. This sensitivity causes sweat secretion independent of overall body temperature.
Measuring Electrodermal Activity
The measurement of skin conductance is often referred to by the broader term, Electrodermal Activity (EDA), or the older term, Galvanic Skin Response (GSR). This measurement is accomplished using two electrodes, typically placed on the fingers or the palm, areas with a high density of eccrine sweat glands. A small, constant, and imperceptible voltage is passed between the electrodes, and the device measures the resulting change in electrical conductivity, which is reported in units of microsiemens (\(\mu\)S).
EDA signals are analyzed by separating them into two main components: tonic and phasic activity. The tonic component, known as the Skin Conductance Level (SCL), represents the slower, baseline level of skin conductivity over time. SCL is thought to reflect a person’s general, sustained level of autonomic arousal, changing gradually over a period of minutes.
The phasic component is the Skin Conductance Response (SCR), which appears as rapid, transient spikes in the signal. An SCR is a momentary increase in conductivity that typically occurs in direct response to a distinct stimulus or event, reflecting a sudden burst of arousal or attention. Researchers often analyze the amplitude and frequency of these SCR peaks to quantify the strength and number of momentary arousal responses.
Practical Applications of Skin Conductance Monitoring
Skin conductance monitoring provides objective data on arousal, making it a valuable tool across several real-world applications. In psychological research, it is used to measure the intensity of a participant’s emotional reaction to various stimuli, such as images, sounds, or tasks. This helps researchers quantify the attention-grabbing or emotionally potent nature of different experimental conditions.
In the field of health and wellness, skin conductance is a component of biofeedback training, where individuals learn to consciously regulate their physiological responses. By seeing their real-time skin conductance data, people can practice relaxation techniques to lower their SCL, aiding in stress management and anxiety reduction. Wearable devices increasingly integrate EDA sensors to monitor and track stress levels during daily life and sleep.
Consumer neuroscience and marketing studies utilize skin conductance to gauge a person’s subconscious engagement with products, advertisements, or user interfaces. By monitoring SCRs, researchers can identify which specific moments or elements capture a person’s attention or generate an emotional response.
In clinical settings, skin conductance is used in pain research as a measure of physiological arousal in non-communicative individuals. This includes patients such as infants or those under general anesthesia.