Moulds are simple, microscopic organisms that can grow virtually anywhere, both in homes and outdoors. Along with mushrooms, yeasts, and mildew, moulds are classified as fungi.

Moulds typically consist of a network of threadlike filaments that infiltrate the surface on which the mold is growing. Moulds reproduce by releasing spores, which are lightweight and small enough to travel through the air.

Spores can resist dry, adverse environmental conditions, allowing them to outlive the mold that produced them.

Moulds according a report by Alliance for healthy Homes play an important ecological role in breaking down dead organic matter and returning nutrients to the environment.

They require moisture and food to grow, and they typically thrive in warm, moist environments. Moisture is the key factor determining mold growth in the home, influencing both the types of mould present and the extent of mould colonization.

A variety of materials found in the home, including insulation, wallpaper, glues used to affix carpet, backing paper on drywall, dust, and dirt, can serve as a food source for mould. Mould colonies can go dormant under adverse conditions and revive when favorable conditions return.

Mould growth often appears as green, gray, black, brown, or other discoloration. Eventually, mould growth results in the breakdown of the substrate.

People are exposed to mould on a daily basis. Most exposures in the home occur when occupants inhale spores or mould fragments, which are components of household dust. They also may be exposed when their skin comes into contact with mould-contaminated materials.

Most people according to the Alliance in its website http://www.afhh.org, are unaffected by exposure to moderate amounts of mould. However, mould exposure can cause allergic reactions in some people.

Approximately 6-10 percent of the general population, and 15-50 percent of persons who are genetically prone to develop allergies (atopic individuals), are allergic to mould, according to the US National Academy of Sciences.

The most common symptoms include runny nose, eye irritation, coughing, congestion, and exacerbation of asthma in persons who have the disease. At this point, it is unclear whether mould can cause individuals to become asthmatic.