Mould

Mould is a common fungus that grows in damp and moist environments.  Normally entering properties as spores which float in through open doors and windows.  If the environment is right it will germinate and grow creating branching, thread-like cells called hyphae, which weave together to create the feeding network known as mycelium,

Indoor air quality tests are all important in testing for mould, as you cannot rely on visual sightings.  Spores, the dangerous element is invisible to the eye being 1 to 3 micron.  Spores can remain airborne within a property indefinitely without detection, Due to their microscopic size, they are easily inhaled, causing a range of symptoms to exposed individuals.  

The problem will be moisture related with the most common being condensation forming on cooler surfaces due to excess humidity.  Many will sight lack of ventilation, but this will only apply if there is an imbalance  between indoor and outdoor moisture levels.  Most likely is wall moisture, leaks, inefficient air extraction from kitchen and bathrooms, external drainage or lateral / capillary damp.  Whatever is responsible must be found and corrected.

Fact.  You cannot eradicate mould by cleaning, as the main problem is the airborne spore as it is the seed it will simply reestablish itself.

BMT / pureAzone uses electronic sterilisation which byway of an accelerator that disrupt microbial DNA, therefore effectively killing pathogens that are airborne or embedded in fabrics. High heat pads reaching over 100c are used for solid objects to kill fungi roots. After which a complete air exchange with high powered commercial units to remove any dead airborne or surface fragments.