Any rain or melting snow, followed by a humid summer gives you perfect conditions for mold and mildew growth. Adams says the causes of most mildew problems are not difficult to understand or to solve. Air can absorb moisture.
Warm air can hold more water vapor than cold air.
When the temperature of the air drops, its ability to hold moisture is lessened until the air reaches the dew point. Droplets of water will form on any surface that is at or colder than the dew point of the surrounding air. Adams says mold spores grow especially well on a dirty surface. The first reflex when people smell mold is to throw open the windows, which is exactly the wrong thing to do. Schadler warns that most dehumidifiers have water pans that hold far less than the machine can extract from the air.