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HomeLearn MoreMold in Homes

Mold in Homes and Their Hazard Classes

Learn more about:

Hazard Classes of Indoor Mold

In some countries indoor molds have been grouped into 3 hazard classes based on associated health risk. These classes are similar to risk groups assigned to microorganisms 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 buildings 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.

Molds commonly found in kitchens and bathrooms

Cladosporium cladosporioides (hazard class B)
Cladosporium sphaerospermum (hazard class C)
Ulocladium botrytis (hazard class C)
Chaetomium globosum (hazard class C)
Aspergillus fumigatus (hazard class A)

Molds commonly found on wallpapers

Cladosporium sphaerospermum
Chaetomium spp., particularly Chaetomium globosum
Doratomyces spp (no information on hazard classification)
Fusarium spp (hazard class A)
Stachybotrys chartarum (hazard class A)
Trichoderma spp (hazard class B)
Scopulariopsis spp (hazard class B)

Molds commonly found on mattresses and carpets

Penicillium spp., especially Penicillium chrysogenum (hazard class B)
and Penicillium aurantiogriseum (hazard class B)
Aspergillus versicolor (hazard class A)
Aureobasidium pullulans (hazard class B)
Aspergillus repens (no information on hazard classification)
Wallemia sebi (hazard class C)
Chaetomium spp., particularly Chaetomium globosum
Scopulariopsis spp.

Molds commonly found on window frames

Aureobasidium pullulans
Cladosporium sphaerospermum
Ulocladium spp.

Molds commonly found in basement (cellars)

Aspergillus versicolor
Aspergillus fumigatus
Fusarium spp.

Molds commonly found in flower pot soil

Aspergillus fumigatus
Aspergillus niger (hazard class A)
Aspergillus flavus (hazard class A)