"An exhaustive review of the scientific literature made it clear to us that it can be very hard to tease apart the health effects of exposure to mold from all the other factors that may be influencing health in the typical indoor environment," said committee chair Noreen Clark, dean, School of Public Health, University of Michigan, Ann Arbor. "That said, we were able to find sufficient evidence that certain respiratory problems, including symptoms in asthmatics who are sensitive to mold, are associated with exposure to mold and damp conditions. Even though the available evidence does not link mold or other factors associated with building moisture to all the serious health problems that some attribute to them, excessive indoor dampness is a widespread problem that warrants action at the local, state, and national levels."

Excessive dampness influences whether mold as well as bacteria, dust mites, and other such agents are present and thrive indoors. Moreover, wetness may cause chemicals and particles to be released from building materials. Many studies of health effects possibly related to indoor dampness do not distinguish the specific health effects of different biological or chemical agents.

Through its careful review of the available scientific studies, the committee found sufficient evidence to conclude that mold and damp conditions are associated with asthma symptoms in asthmatics who are sensitive to mold, and to coughing, wheezing, and upper respiratory tract symptoms in otherwise healthy people. However, the evidence did not meet the strict scientific standards needed to establish a clear, causal relationship. An uncommon ailment known as hypersensitivity pneumonitis also is associated with indoor mold exposure in genetically susceptible people. Damp conditions and all they entail may be associated with the onset of asthma, as well as shortness of breath and lower respiratory illness in otherwise healthy children, although the evidence is less certain in these circumstances. Likewise, the presence of visible mold indoors may be linked to lower respiratory tract illness in children, but the evidence is not as strong in this case.

The committee found very few studies that have examined whether mold or other factors associated with indoor dampness are linked to fatigue, neuropsychiatric disorders, or other health problems that some people have attributed to fungal infestations of buildings. The little evidence that is available does not support an association, but because of the dearth of well-conducted studies and reliable data, the committee could not rule out the possibility.

Studies on animals and cell cultures in labs have found toxic effects from various microbial agents, raising concerns about whether these same agents growing in buildings can cause illness in people. Molds that are capable of producing toxins do grow indoors, and toxic and inflammatory effects also can be caused by bacteria that flourish in damp conditions, the report noted. Little information exists on the toxic potential of chemicals or particles that may be released when building materials, furniture, and other items degrade because of wetness. The committee recommended that current animal studies of short-term, high-level inhalation exposures to microbial toxins be supplemented with new research that evaluates the effects of long-term exposures at lower concentrations.

Moisture and mold problems stem from building designs, construction and maintenance practices, and building materials in which wetness lingers. Technical information describing how to control dampness already exists, but architects, engineers, building contractors, facility managers, and maintenance staff do not always apply this knowledge, the report says. Training curricula on why dampness problems occur and how to prevent them should be produced and disseminated. Guidelines for preventing indoor dampness also should be developed at the national level to promote widespread adoption and to avoid the potential for conflicting advice from different quarters. In addition, building codes and regulations should be reviewed and modified as necessary to reduce moisture problems.

Research on various means to prevent or eliminate excessive dampness -- including educational initiatives and building renovations or design changes -- should be undertaken to find out which are effective. While there is universal agreement that promptly fixing leaks and cleaning up spills or standing water substantially reduces the potential for mold growth, there is little evidence that shows which forms of moisture control or prevention work best at reducing health problems associated with dampness, the report notes. In addition, materials designed to educate the public about the actual health risks associated with indoor dampness should be developed and evaluated. The effectiveness of economic and other incentives to spur adherence to moisture prevention practices -- such as bonuses for facility managers who meet defined goals for preventing or reducing problems, or fines for failure to correct problems by a specified deadline -- should be evaluated, and successful strategies should be implemented.

The committee had insufficient information to recommend either an appropriate level of dampness reduction, or a safe level of exposure to organisms and chemicals linked to dampness. Better standardized methods for assessing human exposure to these agents are greatly needed, the report says. It calls for studies that compare various ways to limit moisture or eliminate mold and to evaluate whether the interventions improve occupants' health.

The study was sponsored by the Centers for Disease Control and Prevention. The Institute of Medicine is a private, nonprofit institution that provides health policy advice under a congressional charter granted to the National Academy of Sciences. A committee roster follows.