Mold (a type of fungi) is everywhere.  They are a normal important part of our natural environment.  They are nature's garbage collectors, very opportunistic, many of the building materials we use in our homes are a perfect food source for fungi.  Thus, to keep them from proliferating, moisture must be kept at low levels (35-45% relative humidity (RH)).  Fungi can proliferate in all of the following areas if they become wet or damp:

Latex paint	Office dividers	Drywall
Wood molding	Furnace filters	Carpet/Pad
Ceiling tiles	Material furnishings	Clothing/Shoes
Paper products	Resilient flooring backing	Insulation