Fungi include moulds and yeasts and are ubiquitous in nature – that is they occur everywhere. Every environment has its normally occurring fungi. They serve as natural “recyclers” – helping to break down waste and refuge so that the natural cycle of life can revolve. Without fungi, the world would not be as we know it – forests would die, crops would not mature, flowers would not bloom.

There are many fungi - they are named as different genera (family name) or species (given name) – just like us except the genera (family) name is usually given first.


Normally, our everyday low level indoor and outdoor exposure to surface and airborne mould present little or no health risk. However, if buildings (or our homes) become “wet/elevated moisture” and have allowed un-healthy fungi to dominate, this can create an environment with the potential to greatly affect human health. This is the case when the levels discovered in our environment are found to be high and when specific genera are found to be predominant.

The major factors which determine if mould will grow are temperature and moisture. When it is allowed to grow, reproduction of most moulds is in the form of spores which are spread via airborne dispersal or through insects. Mould growth can rapidly occur due to the presence of moisture (e.g. when the relative humidity is 60% or higher or the surface of the timber, plasterboard, concrete – floor/ceiling or contents including carpet have elevated

What is mould?

Mould is a type of fungus. It grows on surfaces in masses of branching threads which resemble dense cobwebs. The fertile threads, those which have spores, often stand up from the surface into the air to release their spores. Spores are carried by air currents and consequently can spread quickly throughout a book collection.

Where does it come from?

The spores of fungi that become mould or mildew are always present in the air and on objects. When the temperature and moisture in a book collection environment are suitable for germination, the fungus spore bursts and grows into a thread-like filament called a hyphae. The organic material of books is its food source and within a short period it begins to produce spores thereby spreading fungi throughout a book collection.  

Environment which favours growth of mould!

The most important environmental factor to control is the amount of moisture in the air and consequently in books and paper. Books and paper naturally contain an amount of water. They are hygroscopic, so that when the relative humidity (RH) goes up, they absorb water to achieve equilibrium. At 50% RH, the moisture content of paper is approximately 7%; at 70% RH, it is approximately 10%. Moisture enables mould to absorb nutrients from books and paper substrates, so the more moisture a book contains, the greater are the chances for fungus spores to germinate at room temperature. The potential for mould development on wet books is one important reason why books need to be dried immediately or preserve in a freezer.

Most mould thrives in warm temperatures. When combined with high levels of humidity, temperatures of 21 to 24 degrees Celsius can cause mould to develop. Temperatures below freezing will not kill mould, but they do make it dormant.

What to do when you have a mould outbreak

In buildings that house book collections, customer comfort (normal air conditioner systems range between 21-24 degrees Celsius) in times of high RH (60% upwards) creates ideal environments for mould to germinate. If you encounter active mould (normally visible on the spine of books first), isolation of affected material is suggested. If a small quantity of books is mouldy (10 or less), seal them in an air-tight plastic bag.

If the infestation is larger, quarantine the area. Isolating mouldy books and papers serves two purposes: it minimizes the spread of mould, and it protects those persons who may have allergies or respiratory problems from harm. Then contact a qualified mould remediation company ASAP.