Mould spores (like “seeds”) are found, literally, everywhere, including in our homes. In our homes, there are ample amounts of organic material, “food” for mould, such as wood, paper, cardboard, cotton, wool, linen, and many, many things that are organic. “Dirt” contains particles of organic material and dirt is a common food source for many moulds. Many moulds thrive in the temperature range of 20C-30C, and our homes are typically kept inside of that range. The only thing missing for mould to thrive is “water!” If there is a leak or broken hose or pipe, or even high humidity (over 60%RH) then mould has enough moisture to begin to grow.