How to determine types of mold growing in a house

Updated February 21, 2017

Around 1,000 different types of mould can be found in houses. Molds are divided into three major categories: allergenic moulds, which are not life-threatening and tend to only affect people with allergies or asthma; pathogenic moulds, which cause infections in people with compromised immune systems; and toxic moulds, which cause serious health problems, even death. The most common types of mould that grow inside houses are aspergillus, alternaria, cladosporium, Stachybotrys atra, mucor and penicillium. Because many moulds look extremely similar, you can usually determine what types of mould are in your house by the location where the mould is growing.

Identify alternaria mould in your house by looking for it in carpets, window frames, cloths and horizontal surfaces. You can also find alternaria outside your home growing on soil and plants.

Determine whether you have aspergillus growing in your house by looking for it on decomposing vegetables, stored food and soil. Penicillium also forms on decaying foods (this is the mould that grows on old bread) and soil, but it can also grow on dust, carpet, wallpaper and fibreglass duct insulation.

Look for cladosporium on fibreglass duct liners and inside supply ducts. Cladosporium also grows on dead and woody plants, food, soil, paint and cloth.

Identify Stachybotrys atra, more commonly known as "black mould," by its trademark dark colouring. Stachybotrys grows on wood building materials or other wet cellulose materials. You can usually find this mould growing under ceilings and behind walls.

Find mucor by looking for mould growing on animal faeces, such as in your cat's litter box. Mucor is also found in dust and soil.


If you're uncertain about what type of mould is growing in your house, have the mould inspected by a professional mould-removal service or an environmental agency.


If you believe you have Stachybotrys atra ("black mould") growing in your house, leave your house and contact a mould-removal company right away. Black mould is extremely harmful and can even lead to death in animals and infants by causing bleeding in the lungs. Don't attempt to clean pathogenic or toxic moulds. Contact with or breathing in these moulds is extremely harmful, and you'll likely need to contact a professional mould-removal service to evaluate the mould and remove it from your house.

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