Common Types of Household Mold
Seven mold species account for most of what grows in American homes. They differ in where they take hold, what they look like, and what they do to people. This page is the reference. If you already know what you are dealing with and want to remove it, start with our guide to cleaning up mold in your home.
Mold is a fungus, in the same biological family as yeast and mushrooms. It grows in thread-like structures called hyphae. Individual structures are too small to see, so what you notice is a colony, usually black, blue, or green depending on what the mold is feeding on.
It needs four things: water, a food source, oxygen, and a temperature roughly between 40 and 100 degrees Fahrenheit. Indoors, the food is almost always something organic. Paper and wood products are the obvious ones, which is why drywall is so vulnerable, and mold will also digest adhesives, paint, and paste. It cannot feed on metal, glass, plastic, or concrete, but it will happily feed on the layer of dust sitting on top of them.
Water is the variable you control. Mold does not need a leak. It can pull enough moisture straight out of humid air, and it generally starts growing once relative humidity passes 60%. That single number is why humidity control does more to prevent mold than any cleaning product.
The Seven Types at a Glance
| Species | Where you find it | Appearance | Health notes |
|---|---|---|---|
|
Stachybotrys "black mold" |
Wood, paper, cardboard, hay. Needs sustained heavy damp. | Dark, often slimy | Produces mycotoxins. The species behind most "toxic mold" coverage. |
| Aspergillus | Very common indoors. Dust, damp walls, insulation. | Varies widely by species | A genus of 180 to 300+ species. Fewer than 40 cause infection in humans. |
| Cladosporium | Common indoors and out. Fabrics, carpets, damp wood. | Olive-green to brown or black | Associated with skin lesions, nail fungus, asthma, and lung infections. |
| Mucor | Soil originally. Indoors, ductwork and air conditioning systems. | Whitish or grey, thick, fast-growing | Grows quickly once established. |
| Penicillium | Walls, food, water-damaged materials. | Blue-green, often fuzzy | The genus penicillin comes from. Useful in medicine, a health issue in a house. |
| Acremonium | Humidifiers, drain pans, window sealants, cooling coils. | Small, moist at first, then powdery | Produces potent toxins affecting immune system, organs, and bone marrow. |
| Fusarium | Soil and plants. Indoors, humidifiers and water-damaged materials. | Pink, white, or reddish | Produces toxins affecting circulatory and nervous systems. Usually via ingestion. |
You cannot reliably identify a species by looking at it. Color and texture overlap heavily between them, and the same species varies depending on what it is growing on. If identification matters, for an insurance claim or a health situation, that needs a lab test rather than a photo comparison.
The practical point is that identification rarely changes what you do. Removal is the same process regardless of species, and the health advice is the same: reduce exposure and fix the moisture.
The Seven Types in Detail
Stachybotrys
Grows readily on wood, hay, paper, and cardboard. This is what people mean by "black mold" or "toxic mold," though both are informal terms applied loosely to several different species. Stachybotrys needs sustained heavy damp, often days or weeks, to establish.
It also turns up in office buildings, usually where poor ventilation meets a standing indoor water source such as a decorative fountain. Water features look good and create exactly the humidity and temperature conditions this species wants.
For removal, see our step-by-step guide to getting rid of black mold, including when the job is beyond DIY.
Aspergillus
One of the most common household molds, and a genus rather than a single species. Estimates run from roughly 180 to over 300 distinct species depending on how modern genetic classification draws the lines. The CDC puts the number known to cause infection in humans, a condition called aspergillosis, at fewer than 40.
That spread is why generalizing about Aspergillus is difficult. Most species are harmless to a healthy adult. A small number are serious for someone with a compromised immune system or an existing lung condition, and those are the ones worth taking seriously.
Cladosporium
Common both indoors and outdoors, and it has a rough reputation for good reason. It has been linked to skin lesions, nail fungus, asthma, and lung infections. Unlike most household molds it will grow in cool conditions, so a cold basement is no protection.
Mucor
Originally a soil mold that finds its way inside. It shows up most often in ductwork and inside air conditioning systems, where condensation gives it the moisture it needs. It grows fast, appears whitish or grey, and can build up thick.
Mucor in an HVAC system is worth taking seriously, because the system then distributes spores through the whole house every time it runs.
Penicillium
The genus that gave us penicillin, used routinely in food processing and medicine. Growing on your walls it is a different proposition. It spreads quickly across water-damaged materials and is a common cause of indoor allergy symptoms.
Acremonium
Troublesome out of proportion to how often it is discussed. It produces potent toxins capable of damaging immune systems, organs, and bone marrow, and has been linked to impaired cognitive function. It favors humidifiers, drain pans, window sealants, and cooling coils, all places nobody inspects.
Fusarium
Another soil mold, typically arriving on plants or in humidifiers. It produces toxins affecting the circulatory and nervous systems. Exposure is usually through ingestion, contaminated grain being the classic route, though inhaling the spores can cause problems too.
What to Do Next
Identifying the species is interesting and rarely decisive. What matters is the sequence, and it is the same for all seven.
- Fix the water. Every species on this list needs moisture. Without it, none of them establish. Our guide to dehumidifiers and air purifiers for mold covers humidity targets and dehumidifier sizing.
- Remove what you can see. Hard surfaces get cleaned. Porous materials that mold has grown into usually get cut out and replaced. Our step-by-step mold cleanup guide covers what to use on each surface.
- Clear the air. Cleaning mold releases far more spores than leaving it alone does, and they stay airborne for hours. A HEPA air purifier captures them before they settle and start again. See our air purifiers for mold.
- Know when to stop. More than about 10 square feet of visible growth, mold inside HVAC, or mold following sewage or flood water is a job for a remediation professional.
Frequently Asked Questions
What are the most common types of household mold?
Seven species account for most indoor mold in homes: Stachybotrys, Aspergillus, Cladosporium, Mucor, Penicillium, Acremonium, and Fusarium. Aspergillus and Cladosporium are the two you are most likely to encounter. Stachybotrys, commonly called black mold, gets the most attention but is less common because it needs sustained heavy dampness to establish.
How many types of Aspergillus mold are there?
Aspergillus is a genus containing somewhere between 180 and more than 300 species, with the exact count depending on how modern genetic classification separates them. The CDC puts the number known to cause infection in humans at fewer than 40. Most species are harmless to a healthy adult, which is why a positive test for Aspergillus on its own says little without knowing which species and who is exposed.
How can I tell what type of mold I have?
Not reliably by looking at it. Color and texture overlap heavily between species, and the same species looks different depending on what it is growing on. Laboratory testing is the only accurate method. In practice identification rarely changes what you do, because removal is the same process regardless of species and the health guidance is the same: reduce exposure and fix the moisture.
Is black mold worse than other types of mold?
Stachybotrys produces mycotoxins, which is the basis for its reputation, and it deserves to be taken seriously. Several other species on this list also produce toxins, including Acremonium and Fusarium. Any significant mold growth in a home warrants the same response regardless of species, and the color of a colony tells you very little about which species it is.
What conditions does household mold need to grow?
Water, a food source, oxygen, and a temperature roughly between 40 and 100 degrees Fahrenheit. Water is the one you control. Mold does not require a leak, since it can draw enough moisture from humid air, and it generally begins growing once relative humidity passes 60%. Holding indoor humidity between 30% and 50% prevents nearly all household mold.
Which mold grows in air conditioning and ductwork?
Mucor most often, because condensation inside an HVAC system gives it the moisture it needs. This is worth addressing promptly, since the system then distributes spores through the entire house every time it runs. Acremonium also favors cooling coils and drain pans.
Do air purifiers remove different types of mold?
A HEPA air purifier captures airborne spores from any mold species. Spore size varies between species but all of them fall well inside what HEPA filters trap. What an air purifier cannot do is remove mold from a surface or fix the moisture that caused it. It handles what is in the air, which is what causes symptoms and what spreads growth to new areas.
