There are many variations of mould types that are commonly found in homes, all of which are potentially dangerous to humans and animals, and that’s why it’s ever so important to treat and remove mould as soon it’s been discovered.

Most people describe the types of mould by colour, which is black, white, green, grey or brown. But the reality is, the colour rarely tells you how potentially harmful the mould is. There are dangerous and harmless kinds of moulds in each colour group. Regardless of the type of mould, it should be treated as potentially a health hazard and should be removed from your home.

Mould danger classes

In some countries mould is categorised into 3 classes of danger based on health risk.

  • Class A: the most dangerous type of mould, which should not be present in your home as they can pose a serve health risks, such as infections and/or creations of toxins. If found, it should be dealt with carefully and removed immediately.
  • Class B: This type of mould also pose health risks, like allergic reactions and skin irritations. The effects commonly occur over long periods of time.
  • Class C: This type of mould is not dangerous to humans health, however, they can cause damage to your home (structural damage), so still needs to be removed.

Common moulds found in homes

Here’s a list of the most common moulds found in homes, with a brief descrption…


This type of mould can be found in many places, it’s believed to contain about 100 species. It’s commonly in insulation, carpets and mattress dust, damp or wet walls (especially in basements) and wallpaper.

It can look brown, grey and white, and various types can be found in all three danger classes.


Another widespread mould, which is believe to contain 40-50 species.

Usually appears black or grey on surfaces. It’s not commonly found in the home, but if it is, it most likely originated from outdoor sources.

It has a danger class of B, and is known to cause allergic reactions.


This is one of the most common types of moulds, which often appears green, brown, grey or black and includes about 40 different specifies.

Cladosporiumis is very commonly found on wet surfaces, such as painted walls, wood, wallpaper, carpet and mattress dust.

It has a danger class of B or C, depending on species. Some species are capable of triggering allergic reactions to sensitive individuals, and prolonged exposure can lead to asthma attacks.


There are about 200 different species of Penicillium, and it can be found everywhere in the air and soil.

This type of mould is often responsible for causing food spoilage, and is an indicator organism for dampness indoors. It is extremely common on damp surfaces, including walls and wallpaper, floor, carpet mattress and upholstered furniture dust.

Some species are known to produce toxic compounds, and the spores can trigger allergic reactions in individuals sensitive to mould.

It can appear blue, yellow, green or white. It has a danger class of A or C.


One of the most dangerous types of mould- it’s the notorious “black mould” that is often associated with adverse affects to human health. But please note, there are several moulds that appear black and most of them are relatively harmless, however, Stachybotrys can be extremely dangerous. It is one of the most feared mould types.

It’s found in extremely damp areas and has a dangerous class of A, which means it can cause infections and create toxins.


Commonly found in damp or wet areas such as bathrooms, kitchens and basements and around windows. It grows on very wet walls because it requires a lot of water, which makes it an excellent indicator of water damage.

It’s been reported

Ulocladium has been known to cause hay-fever allergy and skin infections. It is classified as a Class B danger mould.

Which type of mould do you have?

If you want to find out what type of mould you have in your home, you can do either of the following:

  1. Purchase a home mould testing kit and send a sample to a facility that specialises in testing mould.
  2. Call a professional mould service to collect samples and then they will either send it to a lab or test it themselves (this is generally more expensive than buying a testing kit yourself and sending it to a lab). Using a professional mould tester for collecting and analyzing mould samples will always provide the most accurate set of results.

In extremely difficult to test mould yourself, as it requires expert knowledge and equipment. For more information, go to the mould testing page.