While there remain many unresolved scientific questions, we do know that exposure to high level of molds causes some illnesses in susceptible people. Because molds can be harmful, it is important to maintain buildings, prevent water damage and mold growth, and clean up moldy materials.

Molds are ubiquitous in nature and grow almost anywhere indoors and outdoors. More than 1,000 different kinds of indoor molds have been found in U.S. homes. Molds spread and reproduce by making spores, which are very small and lightweight, able to travel through air, capable of resisting dry, adverse environmental conditions, and hence capable of surviving a long time. Molds need moisture and food to grow, and their growth is stimulated by warm, damp, and humid conditions.

We also know that molds can cause illness when people are exposed to extensive mold growth indoors. In its 1993 report "Indoor Allergens," the Institute of Medicine (IOM) concluded that airborne fungal allergens were most often associated with allergic diseases, such as allergic rhinitis/conjunctivitis, allergic asthma, and hypersensitivity pneumonitis. In its 2000 report "Clearing the Air: Asthma and Indoor Air Exposures," IOM concluded that there is sufficient evidence of an association between exposure to mold and exacerbations of asthma.