It may be worth clarifying what most people mean by condensation in a clothing system. It's fairly obvious when you see it because you will find very small droplets of moisture, often forming on loose fibres that aren't in contact with other layers. It is moisture that was in the air and has condensed again.
Sweat may be a cause of condensation as it evaporates and passes through your clothing system, condensing on an outer layer.
We are losing moisture through our sweat glands all the time. This is called insensible sweat. When we are hot the skin can be wet with sweat which is much more obvious.