Sources: These organisms can grow almost anywhere, and their spores are nearly everywhere. Moisture is an essential ingredient for the growth of mold, mildew, etc. Organisms will also grow in stagnant water. Growth of these microorganisms is mainly a nuisance, in terms of unpleasant odors and destruction of materials. Sometimes problems can be more serious, involving health problems and structural damage to buildings (rotting wood).
Health Effects: These usually become important when molds or by-products are dispersed so that they are inhaled by people (mold growth in duct work, drip trays under air conditioning units or refrigerators). Some humidifiers can disperse large amounts of mold growth via droplets of water.
Solutions: Solve building moisture problems to decrease humidity. Make sure drip trays are emptied regularly or drain properly. Clean humidifiers regularly; add fresh water daily.