A galvanic skin response (GSR) is a change in the electrical conductance of your skin caused by sweat gland activity. When you experience stress, excitement, fear, or any form of emotional arousal, your nervous system activates sweat glands, and even a tiny, imperceptible increase in moisture makes your skin conduct electricity more easily. That shift is measurable, and it gives researchers, clinicians, and even consumer devices a window into your body’s automatic stress reactions.
How Your Nervous System Controls It
Your central nervous system sends signals through the sympathetic nervous system, the branch responsible for your fight-or-flight response, to activate eccrine sweat glands across your body. During emotional sweating (as opposed to the kind that cools you down on a hot day), stress hormones like noradrenaline stimulate both eccrine and apocrine glands. Even if you don’t feel yourself sweating, these glands release enough moisture to change the electrical properties of your skin’s surface.
The key point is that this process is involuntary. You can’t consciously control it, which is exactly what makes GSR useful as a physiological marker. Your skin conductance rises whether you want it to or not, making it a relatively honest signal of what’s happening in your autonomic nervous system.
The Two Components of the Signal
GSR isn’t one flat measurement. It has two distinct layers that tell different stories.
The tonic component is your baseline skin conductance level (SCL), the slow-changing background reading that reflects your general state of arousal and thermoregulation. Think of it as the resting hum of your nervous system. It shifts gradually over minutes or hours and varies from person to person.
The phasic component is the sharp, event-driven spike called a skin conductance response (SCR). This is what happens when something specific triggers your sympathetic nervous system: a loud noise, an emotionally charged image, a stressful question. These responses are relatively slow compared to something like a heartbeat. After a triggering event, the conductance increase typically begins within 1 to 4 seconds and peaks around 3 to 6 seconds later. In certain testing scenarios, the response can start within 1 to 2 seconds and reach its maximum around 5 to 7 seconds.
How It’s Measured
GSR is measured by placing two small electrodes on the skin and passing a very weak electrical current between them. The device tracks how easily that current flows, which changes as sweat gland activity increases or decreases. Results are expressed in microsiemens (a unit of electrical conductance) or kiloohms (a unit of resistance). Higher conductance means more sweat gland activation and more arousal; higher resistance means more relaxation.
Electrode placement matters. The fingertips and the inner side of the foot consistently produce the strongest, most reliable readings across different people. Research comparing multiple body sites, including wrists, fingers, and feet, found that the fingers and feet are the most responsive to emotional stimuli. Wrist-based readings, common in consumer wearables, work but are generally less sensitive than finger or foot placements.
GSR vs. EDA: The Naming Shift
You’ll often see GSR referred to as electrodermal activity, or EDA. EDA is now the preferred scientific term for all changes in the skin’s electrical conductance resulting from sympathetic nervous system activity. “Galvanic skin response” is the older, more widely recognized name that specifically refers to the phasic spikes. In practice, most people use the terms interchangeably, but if you’re reading academic papers or product specs, EDA is the umbrella term you’ll encounter most.
Where GSR Is Used
GSR has a surprisingly wide range of applications, from clinical settings to the device on your wrist.
In psychological research, it’s a standard tool for studying emotional reactions. Researchers use it to measure how people respond to images, sounds, memories, or social situations without relying on self-reporting, which can be unreliable. It plays a role in lie detection (polygraph) testing, where the assumption is that deception triggers measurable sympathetic arousal, though this application remains controversial.
In psychiatry, GSR patterns differ across mental health conditions. People with depressive disorders often show lower baseline skin conductance levels. Those with bipolar disorder, particularly women, tend to have lower initial readings as well. Patients with schizophrenia in remission also show distinct patterns, with initial values that are typically lower or similar to their average response levels during activation. These differences aren’t used for diagnosis on their own, but they help researchers understand how different conditions affect the nervous system.
In biofeedback therapy, GSR gives people real-time information about their stress levels. A relaxation training session might display your skin resistance on a screen: rising resistance means you’re relaxing, while dropping resistance means tension is increasing. Over time, this feedback helps people learn to recognize and influence their own stress responses.
Consumer wearables have brought GSR into everyday life. Devices like the Fitbit use EDA sensors alongside heart rate variability and sleep data to generate stress management scores. Smartwatches that combine EDA with respiratory rate and temperature data are more accurate at detecting psychological stress than those relying on heart rate alone.
Limitations and Accuracy Challenges
GSR is not a perfect window into your emotional state. Several factors can muddy the signal. Movement creates artifacts that look like real responses in the data. Electrode shifts, environmental temperature changes, and baseline drift over time all introduce noise. Traditional analysis methods often struggle to separate meaningful physiological responses from these artifacts, which is a significant limitation for wearable devices worn during daily activity rather than in a controlled lab.
Individual differences also complicate interpretation. Baseline conductance levels vary widely between people, so a reading that signals high arousal in one person might be perfectly calm for another. Factors like skin hydration, ambient temperature, and even the thickness of your skin’s outer layer affect readings. This is why GSR works best when compared against your own baseline rather than measured against a universal standard.
Newer algorithms are improving accuracy by mathematically separating the slow tonic baseline from the fast phasic spikes and filtering out motion artifacts. These advances are making wearable GSR sensors more practical for real-world monitoring outside the lab, but the technology still works best when you’re relatively still and the electrodes have good skin contact.