Water stains under all light switches

From finehomebuilding.com:

"Assuming you run the AC most of the time, the condensation is from outside humidity, not room humidity. When the wind blows, air comes into the house through the outlet boxes. This is "normal" for a poorly-sealed house. If the inside temp is 76 and the dewpoint outside is above that, you will get condensation where the air blows in."

Have they been sprayed with Lysol or something like that recently? I noticed what I thought was water stains one time and opened the cover to find it bone dry. Then my wife remembered she had recently sprayed it with lysol.

My opinion is you have leaky ductwork. So your AC is pulling more air than is being returned creating a mild vacuum in your house which draws moist air in from outside. Outlets and switches are places where it can get in.