How many types of molds and fungi are there?

There are over 100,000 different types of mold. However, not all types of mold pose a threat. Some types of molds are quite benign, and some even have medicinal uses. For example, Penicillium is used in the production of penicillin, an antibiotic commonly prescribed to treat strep throat, bronchitis and other forms of infection.

The problem with the multiplicity of mold species is that it is virtually impossible for an untrained professional to differentiate between toxic molds and household molds. If you discover mold growth in your home, you should call a professional mold removal company to inspect the area and determine if your home requires treatment.

Most common molds and fungi


This mold is usually found in the soil and on dead plants. Indoors, it grows on damp building materials such as drywall ceiling tiles and building paper. Acremonium should be considered an allergen and possibly a pathogen for immunocompromised individuals.


Commonly found in outdoor air, on many types of plants and foodstuffs and prefers decaying agricultural manure. It can be resistant to fungicides. Alternaria is considered an occasional contaminant of water-damaged building materials that contain cellulose. Although Alternaria is a notable source of fungal allergy, pathogenic infections are also reported infrequently.


There is a wide variety of Aspergillus species. Some are considered opportunistic pathogens and can cause lung infections. Some members also produce mycotoxins and have been implicated in causing allergic reactions and hypersensitivity pneumonitis.

Aspergillus-like organisms are among the first fungi to grow on water-damaged materials and are frequently found in water-damaged structures. Although they are commonly found in the outdoor environment, the outdoor frequency is generally considered low.


This yeast-like fungus is commonly found on caulking or wet window frames in bathrooms. Aureobasidium can be pink or black in color. Although it rarely causes infections, it can be allergenic. It is a type of mold. It grows in cooler climates and, along with Cladosporium, is often found on siding.


Survives in the soil. This gram-positive rod is one of a large family of organisms that are mostly non-pathogenic to humans.


Frequently associated with dry rot, Basidiomycetes are primarily fungi, earthworms, fireballs, rusts and tobaccos. High levels of these spores can contribute to allergies in indoor environments. Poria incrassata is a particularly destructive fungal organism that falls under this classification. Poria has caused the collapse of severely infested buildings.


Most commonly associated with plants, Botrytis can cause allergic asthma after indoor exposure. High levels are likely to be found in greenhouses or other indoor areas with high humidity and large numbers of plants.


This is a very common plant pathogen that is commonly found on wood in lumberyards and is embedded in most homes. It has not been well studied and has not been reported as a pathogen or producer of mycotoxins or allergens.


Commonly found on deteriorating wood products, Chaetomium often emits a musty odor and is frequently found on water damaged drywall. Its health effects have not been well studied, but some rare compounds have sometimes been identified as mutagenic.


Cladosporium is the most common genus found in outdoor and indoor air. It is frequently found at high levels in water-damaged environments. Some species may be resistant to certain types of treated wood.


A secondary invader of plant material, Epicoccum can grow at higher temperatures than many fungi, allowing it to be a pathogen of human skin. Colonies produce a wide variety of colors depending on the food source. Although it can be isolated from water-damaged building materials, it is generally considered a typical outdoor organism.


Found in soils and on plants around the world, Fusarium can invade corn and barley and produce toxins at lower temperatures than many fungi. Fusarium has affected water-damaged carpets and various other building materials and can cause infections in immunocompromised people. Its spores are usually slimy and can be difficult to isolate from air samples. It has also been implicated in exacerbating allergies and asthma and can produce mycotoxins.

Gram-negative rods

A group of bacteria commonly found in standing water or waterlogged structures. Most are opportunistic pathogens. Many species release endotoxins that can cause headaches and allergic-type reactions.


Penicillium species are common contaminants on various substances. This organism causes food spoilage, colonizes leather goods and is an indicator organism for indoor moisture. Some species are known to produce mycotoxins.

The health of occupants can be negatively affected in an environment that has an amplification of Penicillium. Penicillium is one of the first fungi to grow on water-damaged materials and has been implicated in causing allergic reactions and hypersensitivity pneumonia. It usually produces a strong musty odor.


Found in wood, soil and decaying plant material, Pithomyces is not known to cause major infections or health problems in humans. It has been found growing on paper but is not commonly found growing indoors.


Frequently found in house dust, soil, fruits, nuts and seeds, Rhizopus often grows in fruit and vegetable waste or forgotten food scraps. Exposure to large numbers of Rhizopus spores has been reported to cause respiratory complications. Rhizopus can be an allergen and opportunistic pathogen for immunocompromised individuals, including those with diabetic ketoacidosis, malnutrition or severe burns.


A common contaminant that can cause toenail infections.


A common soil contaminant. Not pathogenic to humans.

Stachybotrys Chartarum

Stachybotrys grows well on extremely wet building materials containing cellulose that have remained wet for more than a week. It produces mycotoxins that can irritate skin and mucous membranes. A potent mycotoxin produced by Stachybotrys is called satratoxin; it is also toxic when inhaled. Extreme caution should be exercised when this organism is grown indoors.


Opportunistic pathogen. It can survive and grow in nasal secretions and on the skin. It produces many toxins that contribute to its pathogenicity. Coagulase positive are considered potentially pathogenic.

Sterile mycelium

Fungi that are not mature enough to allow speciation.


Generally non-pathogenic. Some species can cause infections in humans. They also produce potentially dangerous mycotoxins. Characteristic odor of freshly tilled soil. Important in the pharmaceutical industry.


One of the most common soil fungi, Trichoderma grows in carpets, on unglazed ceramics and on paper in damp homes. Some species produce metabolites related to trichothecenes, which can be toxic and cause symptoms like those associated with Stachybotrys chartarum. It is also an allergen and can infect immunocompromised individuals.


Isolated from soil, wood and decaying plant material, Ulocladium thrives on high moisture walls and particle board. Because of its high water requirements, it is considered an excellent indicator of water damage. This genus is allergenic, contributing to the allergic load especially in people allergic to Alternaria.


Found worldwide in house dust, air samples, dry food and soil. Wallemia attacks low water activity materials, is an allergen and can produce mycotoxins. It is known to grow on materials with high salt content.


Common in damp habitats and often able to grow at reduced oxygen levels. This organism can cause allergies and can be an opportunistic pathogen.

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