What are skin conductance and skin resistance?

The term skin conductance or skin resistance refers to measurable changes in the electrical properties of the skin. The skin conductance is usually measured in µSiemens. For this purpose, two electrodes are often placed on the index and middle finger.

The skin conductance is the reciprocal of the skin resistance, both are measured quantities of the electric current. More commonly used is resistance, with skin resistance you are dealing with orders of magnitude in the mega and giga ohm range. To illustrate this, it helps to imagine a river. If you stand on the bank of a wide river (smaller resistance), significantly more water can flow past with the same gradient than with a narrow river (higher resistance). It is the same with a river with many obstacles compared to one with few. With the skin, these things are similar, but on a microscopic level, because the moving particles (electrons), i.e. “the water”, are very, very small.

Influence on skin conductance and skin resistance

The change in skin conductance is a good indicator of internal tension, as this is influenced by factors that are subordinate to the sympathetic nervous system. The skin conductance, unlike temperature or breathing rate, is not directly influenced by the body with the aim of changing it. Its change is only a by-product of other regulatory mechanisms.

This explains why both psychological and physical factors have an influence on the skin conductance. Skin resistance as an absolute value says little, but its relative change over time is very significant. Here you can even see how certain influences or thoughts change it.

A low, completely harmless voltage is applied to the skin via the two electrodes of e.g. the eSense Skin Response, over which a very low current flows. The more tense or stressed you are, the moister the skin becomes and the better the current is conducted, so the skin conductance increases as a result. The skin resistance decreases.

Significance of skin conductance in biofeedback training

In the professional, therapeutic field, skin conductance training is the preferred biofeedback training for anxiety, panic and for learning relaxation.

The sweat glands are controlled by the autonomic nervous system (sympathetic nervous system) and react directly to the smallest emotional, physical and mental changes. The increase in skin conductance is clearly visible when exposed to a stress stimulus. This stimulus can be, for example, mental activity, emotional arousal, deep breathing or even a fright.

Even the smallest changes become visible with the help of biofeedback software and can be used for biofeedback training to reduce stress. Further general information on biofeedback can be found here.

Skin conductance in interaction with the psyche

A lowering of the skin conductance (i.e. an increase in skin resistance) is an indication of reduced sympathetic activity and thus also an indication of relaxation of the autonomic nervous system. (There is also an interesting thesis on this here, in German.) The skin conductance is therefore an almost direct indicator of the stress level. Psychological stress sooner or later leads to physical stress. In biofeedback, direct feedback is used; the device detects an increase or decrease in skin conductance and reacts by sending audio-visual or haptic feedback. This signals directly whether the change of state is positive or negative. Through the stimuli thus generated, the body begins to influence the causes.

Of course, these are only ever the causes of physical stress. Even if difficult mental states result in less physical stress through biofeedback than before, one should always go to the deep causes. Poorly functioning relationships, difficulties at work or stress due to overstimulation should always be resolved as well. However, trying to increase stress tolerance enormously, which is possible through biofeedback, is the wrong way in the long run.

How does the measurement and biofeedback training work?

In general, biofeedback works with direct feedback. In this case, the device detects the rising or falling skin conductance and reacts by sending audio-visual or haptic feedback. This signals whether the change of state is positive or negative and through the stimuli thus produced, the body begins to influence the causes.

The measurement is made by passing a minimal current through the skin and measuring the voltage drop, alternatively a voltage is applied and the flowing current is measured, the exact method depends on the particular device.

The eSense Skin Response uses the microphone input of a smartphone, so any voltages and currents that occur are very low, completely harmless and inoffensive in any situation. The use of the eSense Skin Response is as follows:

• Fix the two enclosed Velcro electrodes to your index and middle finger.
• Connect the eSense Skin Response to the microphone input of your device and to the Velcro electrodes.
• Start the app and click on “Start”, this will start the measurement.
• Read the detailed instructions within the app to perform good biofeedback training.

What are the limitations of the training?

Mobility during training

The sensors are attached to the hand, accordingly a cable leads from your hand to the smartphone or tablet. You are minimally restricted in your movement by both the cable and the sensors on your hand. Otherwise, you can move freely, use your body well during training.

Concentration during training

Depending on the training method, you will need to apply a different level of concentration. This is definitely the biggest limitation, due to the constant feedback, training will always slip to the forefront, so dedicated training times where you do nothing or hardly anything else are recommended. However, many simple activities that are rather quiet are excellent for biofeedback training. A good example is travelling by bus and train, one of the perfect opportunities to squeeze in a training session.

Costs

The cost of skin conductance feedback varies depending on the device. As an example, the eSense Skin Response is an affordable single investment.