Modelling the effect of hydration on skin conductivity.

BACKGROUND: Electrical signals are recorded from and sent into the body via the skin in a number of applications. In practice, skin is often hydrated with liquids having different conductivities so a model was produced in order to determine the relationship between skin impedance and conductivity.

METHODS: A model representing the skin was subjected to a variety of electrical signals. The parts of the model representing the stratum corneum were given different conductivities to represent different levels of hydration.

RESULTS: The overall impedance and conductivity of the cells did not vary at frequencies below 40 kHz. Above 40 kHz, levels of increased conductivity caused the overall impedance to decrease.

CONCLUSION: The variation in impedance with conductivity between 5 and 50 mSm-1 can be modelled quadratically while variation in impedance with conductivity between 5 and 5000 mSm-1 can be modelled with a double exponential decay.