Types of Mould
Many people seek to define mould by the colour that it appears: 'green mould' or 'white mould', 'grey mould' or 'brown mould', or, even more general, 'black mould' versus 'non-black mould'. Unfortunately, the colour of a mould rarely tells you anything useful: there are harmful and non-harmful kinds of mould in each colour group. It is difficult to impossible to determine if a mould is harmful based on what it looks like growing on a surface.
This page help you understand the more common moulds out there and their associated hazards. A test from a qualified laboratory can determine whether a mould is known to be toxic or not. For instructions on how you can collect samples and send them to a lab click How To Sample For Mould Using Clear Scotch Tape. Remember!. It's the types of mould and the amounts that you inhale that matters. Consider testing air in your home. For instructions on how to test air click How To Sample Air For Total Fungal Spore Counts. You may also be interested to read Frequently Asked Mould Questions.
Hazard Classes
Some countries have adapted a hazard class system to place moulds in different categories based on their health risks. They are broken into Hazard classes A, B and C:
- Hazard Class A:
Moulds in this group are either directly hazardous to health due to risk of infection or creation of toxins. They should not be in homes or workplaces and should be removed right away if found. - Hazard Class B:
Moulds in this group can cause allergic reactions, especially over longer periods of time. - Hazard Class C:
Moulds in this group aren't known to cause any health risks or reactions in humans. Note, however, that even moulds in this category can potentially cause structural damage to things that they are growing on, and should still be gotten rid of.
Some Common Indoor Moulds
This is a short list of the more common moulds that grow in households. Since moulds are incredibly diverse, even within the individual species, it isn't a complete picture, but it may help in explaining why 'black mould' isn't synonymous with 'dangerous'.
Cladosporium
(pronounced 'clad-oh-spore-ee-um')Cladosporium is a very common mould. It can appear green, brown, grey or black on surfaces. It is classified as either Hazard Class B or C, depending on the species - i.e., allergic reactions are generally the only concern with Cladosporium. It can grow in many places, including walls, wood, dust, and insulation.
Aspergillus
(pronounced 'as-per-jill-us')Aspergillus is another common mould. It can look grey, brown, yellow, green, white, or black. There are many species in the genus, and they generally fall into Hazard Classes A or B. Some can cause infection in people with weak immune systems, and some of them can make toxins in certain circumstances. Others will only cause allergic reactions. Aspergillus can grow on walls, insulation, paper products, soil, clothing, and many other places.
Penicillium
(pronounced 'pen-ih-sill-ee-um')Penicillium is a name that often strikes people as familiar, and that is because modern antibiotics were discovered thanks to a species of Penicillium long ago. However, that doesn't mean that the genus can't be hazardous. It can look blue, green, or white, and its species are generally classified as B or C. It can be found on foods, such as cheese and fruit, or in the walls, the insulation, and other places.
Ulocladium
(pronounced 'you-low-clad-ee-um')Ulocladium usually looks black or grey. It falls into hazard classes B and C, and tends to grow in damp areas. It can be found on walls, around windows, in dusty areas, and other places.
Acremonium
(pronounced 'ack-ri-moan-ee-um')Acremonium is often found on insulation and drywall/sheetrock, although it can be found in many other areas, too - it grows in damp places. It can appear white, grey or brown, and various species are found in all three hazard classes.
Stachybotrys
(pronounced 'stack-ee-bot-riss')
Stachybotrys is the infamous black mould that made the news in association with ill health effects many years ago. It needs a very damp area to grow, and is considered a Hazard Class A mould, as it can create toxins. It looks black on surfaces.
Alternaria
(pronounced 'all-ter-nair-ee-uh')Alternaria looks similar to Ulocladium under a microscope. It can appear black or grey on surfaces. It is classified as a Hazard Class B mould, and has been known to cause various allergic reactions. It can grow on walls, dusty areas, around windows, damp areas, in soil, on plants, and in various other places.
An important side note is that sometimes what you're looking at is actually effluorescence rather than mould. This is a deposit of white salts, especially on concrete, where water has penetrated and left a salt deposit on the surface. It can be difficult to tell.
If you want to find out whether you have a hazardous mould, a harmless mould, or just effluorescence or soot, it's actually very simple, requiring no special equipment. A piece of perfectly clear scotch tape (the cellophane kind, not the 'magic' semi-translucent kind), stuck to the mould, will pick up some of the mould the way that it is growing. It should then be stuck to the inside of a ziplock bag and sealed. There are numerous laboratories that are able to identify a mould from a tape sample. Click here to see the different options for mold testing that you can perform yourself and save money.