Several fungi species produce unhealthy volatile metabolites

From the World Health Organization in its report WHO Guidelines for Indoor Air Quality: Dampness and Mould, published July 16, 2009

2.3.6 Microbial and other volatile organic compounds

Several fungi produce volatile metabolites, which are a mixture of compounds that can be common to many species, although some also produce compounds that are genera- or species-specific. Microbial volatile organic compounds are often similar to common industrial chemicals. To date, more than 200 of these compounds derived from different fungi have been identified (Wilkins, Larsen, Simkus, 2000, 2003), including various alcohols, aldehydes, ketones, terpenes, esters, aromatic compounds, amines and sulfur-containing compounds.

As few of those compounds are specific to fungi, measuring (microbial) volatile organic compounds is therefore of limited use in identifying indoor fungal growth. Detection of specific organic compounds does, however, permit a conclusion of fungal growth  (visible or hidden), even if the results are not quantitative (Moularat et al., 2008a,b). No larger field studies have been conducted to compare mouldy and control buildings, and microbial volatile organic compounds have been measured only rarely in health surveys. Data on airborne concentrations are therefore scarce.

Some exposures with adverse health effects associated with damp indoor environments include emissions of volatile organic compounds from damp and mouldy building materials (Claeson, Sandstrom, Sunesson, 2007). Emissions are a consequence of competition between moisture and some chemicals for adsorption sites. Volatile organic compounds can be similar to microbial ones, as both often occur in the same environment. The main difference is the source of emission, i.e. mould or building materials. Damp concrete floors have been shown to increase chemical degradation of the plasticizer in polyvinyl chloride floor coatings and glues, resulting in emissions of volatile organic compounds such as 2-ethyl-1-hexanol (Norback et al., 2000; Tuomainen, Seuri, Sieppi, 2004). Similarly, damp concrete floors may emit ammonia from the self-levelling flooring compound used in the late 1970s and early 1980s in Europe.

Furthermore, the offgassing of formaldehyde from composite wood products and the rate of formation of ozone increase with relative air humidity (Arundel et al., 1986; Godish, Rouch, 1986). Formaldehyde concentrations may also be elevated in damp indoor environments because moist air holds more formaldehyde. The levels of semi-volatile compounds, such as pentachlorophenol (a wood preservative) and other pesticides, may also be elevated in damp indoor environments. No studies have systematically addressed the link between levels of volatile organic compounds and dampness in indoor environments.