Contributing to limitations in the understanding of the relationship between mold and a number of adverse health effects is the variety of potential disease-causing agents-including many species of mold and other biological agents, such as bacteria or dust mites-that are likely to be present in damp indoor environments.
The number of such agents makes it difficult to know which ones are specifically responsible for the adverse health effects attributed to these environments.
For example, of the approximately 1 million species of mold, there are about 200 species of mold to which humans are routinely exposed, although not all of these are commonly identified in indoor environments, and not all types pose the same hazards to human health.
The mold genus Alternaria, for instance, which has been found in moldy building materials, has been linked to severe asthma. Furthermore, several different components or products of mold, such as mycotoxins, may function as disease-causing agents in indoor environments. The release of these mold components or products varies with environmental and other factors, and the individual roles they may play in adverse health effects are not fully understood.
People are also exposed to mold in outdoor environments, where the concentrations, while they vary considerably, are usually higher than those found indoors. While the specific species of mold that grow indoors may differ from those found outdoors, the potential for outdoor exposure further complicates efforts to determine the relationship between adverse health effects and indoor exposure to mold.
In addition to mold, damp indoor areas can support other biological agents that may result in adverse health effects, including bacteria, dust mites, cockroaches, and rodents. Dust mites, for example, are known to cause the development of asthma. Damp conditions may also lead to potentially harmful chemical emissions from building materials and furnishings. For example, excessive indoor humidity may increase the release of formaldehyde, a probable human carcinogen, from building materials such as particle board. Exposure to formaldehyde has been linked to some of the same health effects that have been attributed to indoor mold, such as wheezing, coughing, and exacerbation of asthma symptoms, as well as more severe effects.
Indoor Mold: Better Coordination of Research on Health Effects and More Consistent Guidance Would Improve Federal Efforts
United States Government Accountability Office