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Common Indoor Moulds & Their Hazard Classes

This is a list of some of the most common indoor moulds and their hazard classes. For an explanation of these hazard classes, read the May 24 post entitled “Indoor Moulds: Hazard Classes And Associated Health Effects”. The list is not exhaustive. At least 150 moulds have been reported from buildings.

Acremonium spp (hazard class B).
Alternaria spp (hazard class B).
Aspergillus flavus (hazard class A).
Aspergillus fumigatus (hazard class A).
Aspergillus versicolor (hazard class A).
Aureobasidium pullulans (hazard class B).
Chaetomium globosum (hazard class C).
Cladosporium cladosporioides (hazard class B).
Cladosporium sphaerospermum (hazard class C).
Fusarium spp (hazard class A).
Mucor spp (hazard class A).
Paecilomyces spp (hazard class B).
Penicillium aurantiogriseum (hazard class B).
Penicillium chrysogenum (hazard class B).
Scopulariopsis spp (hazard class B).
Stachybotrys chartarum (hazard class A).
Trichoderma spp (hazard class B)
Ulocladium botrytis (hazard class C).
Wallemia sebi (hazard class C).

These moulds are commonly found on water damaged or damp surfaces in kitchens, basements, bathrooms, ceilings, and other drywalls. Occurrence of some of these moulds such as Stachybotrys, Fusarium, Ulocladium and Trichoderma in a building is an indication of serious water damage.

Do you have a question concerning indoor moulds? Send your question to My Question.

Which Moulds Grow in Buildings And Why Do They Grow?

The level of moisture (usually referred to as water activity) in building material determines not only whether mould will grow or not but also the types that colonize the material. Damp materials with a water activity value equal to or greater than 0.90 are usually colonized by strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp. Materials with a water activity value ranging from 0.90 – 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.

Water leakage through roofs, defective plumbing installations and condensation are the main sources for water damage with subsequent mould growth. The building materials most susceptible to mould attacks are water damaged, aged organic cellulose containing materials such as wood, jute, wallpaper, and cardboard. Moulds that are most frequently encountered in buildings are Penicillium (68%), Aspergillus (56%), Chaetomium (22%), Ulocladium (21%), Stachybotrys (19%), Cladosporium (15%), Acremonium (14%), Mucor (14%), Paecilomyces (10%), Alternaria (8%), Verticillium (8%), and Trichoderma (7%). These moulds are all known to cause different types of inhalation allergy.

Do you have a question concerning indoor moulds? Send it to us at My Question.

Indoor Moulds: Hazard Classes and Associated Health Effects

Hazard classes of indoor mould
Indoor moulds have been grouped into 3 hazard classes based on associated health risk. These classes are similar to risk groups assigned to micro-organisms handled in laboratory environments.

  • Hazard Class A: includes fungi or their metabolic products that are highly hazardous to health. These fungi or metabolites should not be present in occupied dwellings. Presence of these fungi in occupied building requires immediate attention.
  • Hazard class B: includes those fungi which may cause allergic reactions to occupants if present indoors over a long period.
  • Hazard Class C: includes fungi not known to be a hazard to health. Growth of these fungi indoors, however, may cause economic damage and therefore should not be allowed.

Health Problems Associated With Indoor Moulds
Exposure to indoor mould has been associated with the following health problems:

  • Lower respiratory symptoms such as coughing and wheezing;
  • Respiratory infections such as aspergillosis;
  • Allergic diseases, including allergic asthma and bronchitis;
  • Non-inflammatory, unspecific symptoms, such as eye and skin irritation, fatigue, headache, nausea, and vomiting.

Should you have a question concerning indoor moulds send it to me at My Question.

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