The resistance value of skin typically ranges from 1,000 to 100,000 ohms (Ω), but this value is highly variable and depends on several factors.
Factors Affecting Skin Resistance
Skin resistance is not a fixed value and can fluctuate significantly based on the following conditions:
- Contact Area: Larger contact areas generally result in lower resistance.
- Moisture: Increased moisture (e.g., sweat) dramatically reduces skin resistance. Dry skin has a much higher resistance.
- Skin Condition: Damaged or broken skin offers much lower resistance compared to healthy, intact skin. Calloused skin tends to have higher resistance.
- Pressure: Higher pressure applied to the skin can decrease resistance.
- Voltage: Higher voltages can break down the skin's resistance, although this is dangerous and can cause injury.
- Individual Variation: Differences in skin thickness, hydration levels, and other physiological factors can influence skin resistance between individuals.
- Frequency: The resistance can vary depending on the frequency of the applied voltage/current.
Implications of Skin Resistance
Understanding skin resistance is important in various contexts:
- Electrical Safety: Skin resistance is a primary factor determining the severity of electrical shock. Lower resistance significantly increases the risk of injury.
- Medical Procedures: Procedures like electrocardiograms (ECGs) and electroencephalograms (EEGs) require good skin contact to obtain accurate readings. Skin preparation often involves cleaning and sometimes abrading the skin to reduce resistance.
- Bioimpedance Analysis: This technique measures body composition by passing a small electrical current through the body and measuring the impedance, which is influenced by skin resistance.
- Galvanic Skin Response (GSR): Also known as electrodermal activity (EDA), GSR measures changes in skin resistance related to sweat gland activity, which is often used in lie detection and stress monitoring.
Importance of Considering Internal Body Resistance
It's crucial to differentiate skin resistance from internal body resistance. While skin resistance can be quite high and variable, the resistance of the internal body tissues is relatively low, around 300 ohms. Therefore, once electricity penetrates the skin, it encounters much less resistance, making internal organs vulnerable.
