Pressure of an electric contact and resistance
Simple answer

Pressure increase contact surface area and reduces micro gap of insulation.

Salt (skin) affects conductance or inverse of resistance and pressure increases contact area to reduce resistance. Alcohol cleansed skin can raise R by 1 or 2 orders of magnitude whereas sweaty palms and fingers reduces it.
Moisture affects dielectric (up to 80x) capacitance with again squeezing out the air gaps in fingerprints to increase capacitance where water is 80x more than air but dry skin is more like 10x.
Pressure affects increases both conductance and capacitance. such that RC=T product is pretty constant.
Touch Capacitance sensors are more consistent among humans unless extreme dry skin but resistance is more sensitive but wider variance.  Both need calibration.

Medical patch electrodes use a low galvanic response insulation dielectric jelly with silver particle conductor in the adhesive to improve signal to noise ratio of heart or brain wave electrodes.