If you have central air conditioning, it’s likely that sweat ducts are present. The duct system is made of tiny passageways called pores that carry humidified air to the inner surfaces of your home. As you spend time in these spaces, sweat evaporates from your skin and then accumulates on the inner wall surfaces of the pore structure. Sweat can also accumulate on cold surfaces if they are not warmed up enough by the radiant heat coming off them. If this happens, more moisture will be drawn into those pores which leads to an increase in humidity within these areas or along with increased ambient temperatures inside your home.
Porous Outdoor Air Duct System Ventilation