Indoor mould development and dispersal.

Indoor mould development can occur following the accumulation of free water associated with a susceptible building material. Upon entry of viable fungal propagules from outdoors, the fungus becomes attached to a susceptible substrate. Vegetative growth begins if the appropriate environmental conditions exist, the primary ones being ample free water and a susceptible substrate that can provide the necessary nutrients for fungal growth. Extracellular fungal enzymes are released into the immediate environment surrounding the fungus from which nutrients are absorbed resulting in biodeterioration of building materials. As the fungal vegetative growth expands, fungal reproductive propagules such as conidia, ascospores, basidiospores, and viable hyphal units develop that are typically carried by air currents to new sites within the indoor environment. The indoor fungal ecologic niche is a complex ecosystem where different fungal species interact among themselves and with bacteria, insects, and mites.