Aspergillus versicolor is one of the most common species of indoor mold. Aspergillus versicolor is able to grow on very nutrient-poor materials such as concrete and plaster and is capable of growing at aw < 0.8 (seeming dry or damp condition with no free water). This mold has highly variable culture morphology, but produces a consistent chemical profile on laboratory substrates, usually generating high quantities of the carcinogenic mycotoxins. Aspergillus versicolor produces the mycotoxins versicolin and sterigmatocystin. On wallpaper paste, conidia of 50% of the isolates may contain sterigmatocystin. On water-saturated materials, A. versicolor produces 5-methoxy-sterigmatocystin and sterigmatocystin in quantities up to 7 and 20 µg/cm² respectively, which is up to 1% of its biomass. Exposure to sterigmatocystins might occur via micro-fragments derived from colonies, because very few spores are formed by this species. Interestingly, non-sporulating red-colored samples of contaminated materials contained the largest quantities of sterigmatocystins. Recently, sterigmatocystin was detected in 20% of household dust samples at levels up to 4 parts per billion.

 

Sterigmatocystin is not very cytotoxic by itself, but becomes carcinogenic after activation in the liver by the cytochrome P450 mono-oxidase. In addition to these toxic properties, sterigmatocystin also acts as a strong inhibitor of tracheal ciliary movement. Rats exposed to spores of A. versicolor originating from mold growth on the walls of their cages suffered severe lung damage and developed granulomatous lesions after a month of exposure; these symptoms are thought to have resulted from IL-1 immune system antibody production from activated macrophages. More recently, instillation of single doses of spores has been shown to produce similar effects in mice, with the recruitment of inflammatory cells in the lungs for at least one month. The inflammatory properties were also observed from A. versicolor spores from wet gypsum boards.