Scientific Description of Mold
Molds are composed of linear chains of cells (hyphae) that branch and intertwine to form the fungus body (mycelium). All fungal cell walls contain (1-3)-beta-D-glucan, a medically significant glucose polymer that has immunosuppressive, misogynic (i.e. causing mitosis or cell transformation) and inflammatory properties. This mold cell wall component also appears to act synergistically with bacterial endotoxins to produce airway inflammation following inhalation exposure in guinea pigs (Fogelmark et al., 1994).
Under certain metabolic conditions, many fungi produce mycotoxins, natural organic compounds that initiate a toxic response in vertebrates. While some mycotoxins have been found to be associated with hyphae, the primary mode of human exposure to mycotoxins, is inhalation of spores and mold-contaminated material.
Molds that are significant potential producers of toxins indoors are certain species of Fusarium, Penicillium, and Aspergillus. In water-damaged buildings, Stachybotrys chartarum (a.k.a. atra) and Aspergillus versicolor may also produce toxic metabolites. A large body of information is available on the human and animal health effects from ingestion of certain mycotoxins (Beasley, 1994; Sorenson, 1989; Smith and Henderson,1991), but investigators have only recently begun to explore the health implications of inhalation exposure to these substances.
Two classes of mycotoxins have been isolated from house dust samples: aflatoxins from some strains of Aspergillus flavus and trichothecenes from some species and strains of Fusarium, Cephalosporium, Stachybotrys and Trichoderma. In laboratory animals, inhalation of trichothecene mycotoxins causes severe inhibition of protein synthesis and immune-suppression (Beasley, 1994).
Several case reports have associated overgrowths of trichothecene-producing fungi with human health effects such as cold and flu-like symptoms, sore throats, headache and general malaise (Croft et al., 1986; Johanning et al., 1993; Nikulin et al., 1994). Failure to produce toxins in vitro does not mean that a mold known to be toxigenic will not produce toxins in a field situation.
Molds also produce a large number of microbial volatile organic compounds (mVOCs). These chemicals are responsible for the musty odors produced by growing molds. There is little evidence that fungal mVOCs cause specific human health effects (Batterman, 1995), but the most common VOC, ethanol, is a potent synergy of many fungal toxins.