Mould spores may enter your home through open doorways, windows, heating, ventilation, and air conditioning systems. Spores may also attach themselves to people, animals, toys, shoes, and carry bags bringing the mould indoors.

Many building materials provide nutrients that allow the mould to cultivate when exposed to moisture. Wet materials, including paper products, cardboard, ceiling tiles, and wood products, are primary sites for mould growth. Other materials such as dust, paints, wallpaper, insulation materials, drywall, carpet, and upholstery, also support the growth of mould.