Human exposure to airborne fungal spores, hyphal fragments or metabolites can result in a variety of adverse health effects (Pasanen, 2001). Reactions to exposure include allergic and irritant responses (Gravesen, 1979); infectious disease such as histoplasmosis, blastomycosis, and aspergillosis (de Hoog et al., 2000); a variety of respiratory diseases (Godish et al., 1996a) including asthma (Downs et al., 2001) allergic rhinitis, hypersensitivity pneumonitis (Samson, 1985; Stetzenbach, 1997) and bronchial hyperactivity (Dharmage et al., 2001); acute toxicosis (Samson, 1985; Stetzenbach, 1997); SBS symptoms (Szponar & Larsson, 2000); and cancer from exposure to mycotoxins (Levetin, 1995). Exposure to fungal spores has been identified as statistically significant risk factors for respiratory health in children (Garret et al., 1998a, b). The inhalation of fungal material, which is often small enough to penetrate deep into the lungs, may pose an even greater health risk than ingestion or dermal contact (Johanning, 1994; Stetzenbach, 1997). However, the role of fungi in the development of disease and illness is not clear (Szponar & Larsson, 2000).

Normally, fungal exposure is mostly associated with hay fever, asthma (Levetin, 1995; Stetzenbach, 1997) and allergies (Gravesen, 2000). Spores or fragments of hyphae reach the respiratory tract and lungs, generating allergic responses (Jennings & Lysek, 1999) and up to 15% of the general population have been measured to be allergic to “fungi” (Miller, 1992). The components of most fungi can be antigenic, and fungal spores are well known carriers of aeroallergens (Levetin, 1995). This is due to the fact that the walls of all fungi contain proteins which are potential inducers of IgE-mediated allergy in atopic persons (Gravesen, 2000).

However, the literature on fungal allergens is confusing. Some studies suggest no relationship between fungi and allergy despite the general understanding to the contrary (Tarlo et al., 1988). This may be due to the fact that exposure to fungi does not always cause allergy, as allergy only develops in a sensitised individual (Miller, 1992).

Fungal allergens identified to date are glycoproteins (Levetin, 1995) and a single species of fungi can produce dozens of allergens (Drouhet, 1988). Individual species such as Alternaria species are suggested as the major allergen source associated with the development of childhood asthma (Downs et al., 2001).

Only a small group of fungi are considered human pathogens and very few species are considered primary systemic human pathogens (Levetin, 1995; Stetzenbach, 1997). Most of the fungi that infect humans are opportunistic parasites, which grow more commonly as saprotrophs in soils, composts, bird excreta etc., but can infect through wounds or when airborne spores enter the lungs (Deacon, 1997). Fortunately, fungal pathogens are rarely reported to be present in indoor air (Flannigan, 1994a).

There is also persuasive evidence that exposure to fungi at work is responsible for many cases of illness (Rom, 1983). Mycotoxins, unlike fungal allergens, cause a wide range of chronic systemic effects in humans (Tuomi et al., 2000; Pieckova & Kunova, 2002) and will elicit toxic responses from virtually all individuals who are exposed (Jarvis, 1994). Exposure to mycotoxins in the indoor air is almost exclusively through inhalation of spores containing the toxins and gaseous forms released during metabolism (Tuomi et al., 2000). These toxins attack the bronchial and lung tissues, which are particularly sensitive to chemical insult, and the mucosa lining exhibits strong responses to fungal immuno-active agents (Jarvis, 1994). There are over 400 known mycotoxins (Tuomi et al., 2000) and many fungal species that are common to indoor air produce such toxins, which could be responsible for a variety of health effects (Levetin, 1995). However, few studies have established a causal relationship between mycotoxin exposure and building related illness (Tuomi et al., 2000).

Other metabolites that are volatile can cause unpleasant odours, such as the characteristic mouldy smell in damp basements (Levetin, 1995). Some of these VOCs are short chain alcohols or aldehydes (Samson, 1985) or organic acids (Ström et al., 1994), which may be responsible for symptoms such as headaches, dizziness, and eye and mucous membrane irritation resulting from exposure to fungi in contaminated buildings (Samson, 1985; Burge, 1990; Pasanen, 2001).