Types of Mould

Mould is a type of fungi that can be present indoors and outdoors. Mould is ubiquitous and can grow anywhere there is moisture and dust (source of food). As part of their reproduction, the mould produces spores, which are tiny particles or cells that become airborne. In addition, mould produces mycotoxins, toxic compounds that have harmful or toxic effects on another organism. It is believed that mycotoxins are produced as a strategy to reduce competition from other organisms. (Rudert and Portnoy, 2017).

 A water-damaged building with sufficient moisture in the environment creates an ideal condition for microbial growth – bacteria, fungi, and their by-products (Biljsma 2018). Dampness and mould exposures in buildings are common, with estimates ranging from 18% to 50% of buildings (Gunnbjörnsdóttir et al., 2006; Mudarri and Fisk 2007).

There are approximately 6000 to 10,000 genes identified in fungi. Most fungi do not affect human health. However, there are at least 189 types that have been identified as fungal allergens and a few genera such as Aspergillus, Penicillium, and Cladosporium have been well-characterized. (Rudert and Portnoy, 2017).

The following is the most common mould found in water-damaged buildings:

1. Aspergillus

Aspergillus prefers a warmer climate, making it a common indoor mould type and it is a primary coloniser, that spreads within 48 to 72 hours. The dry spores (mould particles) can exist in large amounts, easily airborne and inhaled. With over 100 different species, Aspergillus can be found in walls, ceilings, subflooring, and HVAC systems.

2. Penicillium

Like other common indoor moulds, Penicillium threatens those with weak or compromised immune systems, causing allergic reactions or infections. It is a primary coloniser, that spreads within 48 to 72 hours. The dry spores (mould particles) can exist in large amounts, easily airborne and inhaled. Penicillium often starts in white colour and then becomes multi-coloured depending on the substrate it is growing on. In addition, some species can cause measurable organ damage. It's most commonly found on soil, decaying vegetation, and compost.

3. Cladosporium

Many species of Cladosporium are commonly found on living and dead plant material. The dry spores (mould particles) can exist in large amounts, easily airborne and inhaled. Cladosporium has a small spore size that is easy to disperse and commonly found in air samples and damp building materials (wallpaper, plaster and timber) It can cause allergies and asthma in some people. In sporadic cases, it can cause infections.

4. Stachybotrys

Often referred to as "black mould" or "toxic mould," A common indoor & outdoor mould type.⁣ They have the ability to produce mycotoxins which may cause a burning sensation in the mouth, throat, and nasal passages. Usually, it's not the fastest type to grow. Instead, it waits to see if there's a significant source of water damage.