Moisture problems are worse where ductwork insulation is on the inside as opposed to the outside of the duct. The insulation's porous surface collects dust and moisture. Mold and mildew may also grow on dirty furnace and air conditioning filters. Plumbing leaks and dampness in attics, basements, and crawl spaces can increase humidity inside your home and promote the growth of agents that will be released as bioaerosols. Bathrooms without outside-vented exhaust fans, combustion appliances like kerosene space heaters, drying laundry indoors, and venting clothes dryers to attics or crawl spaces can also increase the humidity levels in your home.
Dust mites and their waste products are the most common allergens in indoor air.
Dust mites live in rugs and carpets, sheets, mattresses and pillows, and upholstered furniture. Ten to 15 percent of people are allergic to dust mites. First, lower the relative humidity in your home, basement or crawl space, and attic. Relative humidity is the amount of moisture in the air at a given temperature. You may want to see Identifying and Correcting Moisture Problems in Homes.