Moulds are simple, microscopic organisms, present almost everywhere, indoors and outdoors. Moulds break down organic material and recycle nutrients in the environment. Mould needs a food source to grow, which can be any organic material, such as leaves, wood, paper, or dirt, plus oxygen — and moisture. Moulds digest organic material and gradually destroy whatever they grow on.

When damp conditions occur indoors, such as after a flood, roof leak, excessive condensation or any other reason, and wet conditions persist for more than 48-72 hours, mould growth begins and continues for as long as moist conditions are present.