Mould is a type of fungi that has over several hundred thousand species. While many of the species are harmless, there are about 15 different species which are considered to be toxic by releasing mycotoxins, which are harmless to both humans and animals.

How mould develops

Moulds start growing by tiny mould spores floating through the air (they’re literally everywhere- indoors and outdoors) and making contact with damp or wet surfaces (most moulds only require suitable surfaces to be damp/wet for 24 hours before they can grow). If a spore lands on a suitable material and other environmental conditions are suitable then the spore can germinate and begin a new mould colony. Mould requires moisture, oxygen, warmth and food to grow, and they can grow on all surface types, including carpet, paper, clothes, leather, walls, wood, insulation and food.

The spores are invisible to the naked eye; they continually float through the air and it is impossible to eliminate them all from inside your home. However, the best way to prevent mould growing is to limit moisture levels.

If you can see a mould infestation, it is always in colonies, because mould that is not in a colony is too small to see with the naked eye. Mould uses spores to reproduce in the same way that plants use seeds.

Mould biology

A cluster of mould, known as a colony, is considered to be a single organism. The main body (called mycelium) of a mould colony is formed by connected multicellular filaments called hyphae.

Moulds digest the material they are growing on; breaking down decaying organic matter, such as dead plants, leaves or dead animals- that’s where and how they get their energy from (unlike plants getting their energy from the sun through photosynthesis). That’s what makes them particularly

Besides from the organic matter, every type of mould requires moisture for growth. That’s why mould infestations develop in damp areas, particularly in kitchens and bathrooms, where there’s generally a lot of water being used. Mould problems cannot develop in houses unless there is a moisture problem.

Are all moulds dangerous/toxic?

There are many variations of mould types that are commonly found in homes, all of which are potentially dangerous to humans and animals. In some countries mould is categorised into 3 classes of danger- you can find more details on the mould types page.

Most moulds are harmless, but it is advised that all moulds are removed and treated with care, because it’s difficult to determine whether or not the specific mould specie growing in your home is dangerous or not without getting it tested in a lab, under a microscope.

Most people assume that black mould is always toxic. While black mould can be toxic, not all mould that appears black or dark is toxic. But as said, it’s best to treat all moulds as potential health risks.

Some of the most common toxic moulds are:

  • Aspergillus
  • Fusarium
  • Paecilomyces
  • Penicillium
  • Stachybotrys
  • Trichoderma