Sweat ducts make skin a memristor: The researchers attribute skin's memristor behaviour to sweat pores. Sweat contains positively charged ions such as sodium. When skin is exposed to a negative potential, the fluid at the bottom of the sweat pores is drawn upward. Although a thin layer of fluid always coats the inside of the cylindrical pore, this layer thickens as the sweat rises. As sweat is highly conductive, extra fluid rising to the surface increases skin's surface conductivity and thereby lowers its resistance if a subsequent potential is applied.
The longer skin is exposed to a negative potential, the lower the subsequent resistance, until it maxes out when sweat fills the pore. Conversely, a positive potential pushes the ions back, thinning the layer of sweat lining the pore walls and increasing the skin's resistance to current.