Last Updated on May 1, 2025
Mold isn’t just unsightly—it can pose serious health risks if left unchecked. While most homeowners know mold can grow in damp basements or bathrooms, few realize how many different types of mold might be lurking in hidden areas. This updated guide explains the most common indoor mold species, what they look like, where they thrive, and the specific health problems they may cause.
Common Types of Mold Found in Homes
Each mold species listed below is paired with its most common locations, appearance, and health impacts
There are different types of mold that found in homes that many homeowners do not know about. They can pose different health problems to the individuals. The experts are of the view that there are almost hundred different kinds of mold that can be present in a home. Some of the most common ones are discussed below:
Alternaria
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Found In: Bathrooms, under sinks, around leaky pipes
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Health Risks: Asthma, skin irritation, allergic reactions
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Notes: Spreads rapidly in water-damaged environments
This type of mold is usually found outdoors. However, it can also grow in the indoor damp areas. For instance, they can be seen under skins with leaky pipes, in showers etc. the buildings that get flooded or have suffered from water damage tend to become the victim of this type of mold. Alternaria can easily spread from one place to another. Exposure to this type of mold can lead asthmatic problems and allergic reactions.
Aspergillus
This type of mold is usually found indoors. It can cause severe respiratory infections, allergic reactions and can lead to a condition known as hypersensitivity pneumonitis.
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Found In: HVAC systems, walls, ceiling tiles
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Health Risks: Hypersensitivity pneumonitis, lung infections
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Notes: Common indoors; different strains produce mycotoxins
Aureobasidium
This type of mold is found outdoors. However, you can still them indoors if you have painted surfaces, wallpaper or wooden surfaces. Sometimes it is found on the damp window frames and caulking. Generally it is black and pink in color. There are many people who have reported to be allergic to aureobasidium.
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Found In: Painted wood, wallpaper, window sills
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Health Risks: Allergic reactions (especially skin)
- Appearance: Pink to black patches on damp surfaces
Botrytis
This type mold infests in those area where the humidity level is quite high. For instance, bathrooms where there is poor ventilation are an ideal place for this mold to infest. It tends to cause asthma and allergic reactions.
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Found In: Bathrooms, kitchens, laundry rooms
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Health Risks: Asthma flare-ups, eye and skin irritation
- Notes: Loves high humidity; often found on fabrics
Chaetomium
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Found In: Drywall, insulation, paper products
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Health Risks: Skin and nail infections; neurological issues
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Notes: Has a distinct musty odor
This type of mold tends to grow on drywalls that have sustained water damage. Its presence can easily be recognized from the musty odor it produces.
Cladosporium
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Found In: Wood, carpet, floorboards, HVAC
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Health Risks: Throat irritation, nasal congestion, asthma
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Notes: Uniquely tolerant of cold temperatures
Cladosporium is a special type of mold that grows inside homes. Although most of the mold types prefer warm climates, cladosporium has a tendency to grow in cooler regions as well. It is seen to be grown on wood surfaces and carpets, floorboards and cabinets. On the whole, its presence leads to respiratory issues.
Fusarium
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Found In: Damp fabrics, carpet, wallpaper
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Health Risks: Respiratory infections, allergic reactions
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Notes: Grows at low temperatures; spreads quickly
This is more like clasdosporium as it can easily grow in low temperatures as well. Usually it is seen on water-damaged carpets and on some other fabrics. It can lead to respiratory infection and asthma. People who have compromised immune system are known to be vulnerable to infections due to fusarium exposure.
Pencillium
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Found In: Mattresses, insulation, furniture, wallpaper
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Health Risks: Chronic sinus infections, lung inflammation
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Appearance: Green-blue color; spreads aggressively
Penciillium tends to grow in areas that have been damaged by water. It can be mattresses, insulation, wallpaper and carpeting etc. The most important thing about this type of mold is that it spreads easily and very quickly from one part of the home to another. Individuals who get exposed to penciillium complain about chronic sinus infections, allergic reactions and sometimes inflammation of the lungs. It is found in green or blue in color.
Stachybotrys chartarum – Black mold
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Found In: Leaky roofs, air ducts, drywall
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Health Risks: Mycotoxin exposure, chronic fatigue, neurological damage
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Notes: Often called “toxic mold” due to its potent health risks
This type of mold is known as black mold. It has a slimy black appearance from where it has gotten its name. Sometimes, it is also referred as toxic mold. Although the mold itself is not toxic, it produces toxic compounds known as mycotoxins. This compound causes serious health problems in people once they are exposed to it.
The most common ones are breathing problems, allergic reactions, asthma attacks, chronic sinus infections, depression and at times fatigue. It can easily be recognized from its musty odor and is usually grown in those places that stay damp most of the time. The air conditioning ducts and the leaky pipes are their favorite spots.
Serpula lacrymans
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Found In: Structural wood, floor joists
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Health Risks: Structural—not biological. Known for causing dry rot
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Appearance: Yellow mold that degrades timber
It is a yellow mold and results in ‘dry rot’ because it feeds on wood.
Trichoderma
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Found In: Carpets, wallpaper glue, fabrics
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Health Risks: Similar to black mold; produces mycotoxins
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Notes: Allergic reactions are common; may trigger asthma
Wallpapers, damp carpets and other wet areas are its favorite spots. It also produces mycotoxins just like stachybotrys chatarum and lead to severe health issues as well. There are many people who have reported to be allergic to this type of mold.
Ulocladium
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Found In: Flood-damaged walls, wet drywall, basements
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Health Risks: Allergic rhinitis, skin irritation
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Notes: Requires significant moisture to thrive
Since this type of mold needs a lot of water, it only grows in those areas where there is extensive water damage. It can be the homes that are flooded or the wet walls. Just like other types, many people are also allergic to ulocladium.
Efflorescence
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Found In: Basement walls, concrete
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Health Risks: None (not mold)
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Notes: White salt deposits mistaken for mold; water-soluble
Generally, people confuse the salt deposits with the white mold found in basements. You can see the images online and will get to know the exact difference in their appearance.
Why Mold Identification Matters
Each mold species differs in its toxicity and growth behavior. Misidentifying mold can delay proper treatment. If your home has visible mold, professional mold inspection and testing are essential to:
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Determine the mold type
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Measure infestation severity
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Locate hidden mold in walls, HVAC systems, or attic insulation
🧰 What To Do If You Suspect Mold
Don’t wait—mold spreads fast. Contact a certified mold remediation specialist who can:
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Identify the mold species
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Contain and remove it safely
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Prevent recurrence by fixing underlying moisture problems
👉 Need help? Contact the Mold Guy—your Toronto mold removal experts.
