Mould is a generic name for over 000’s different kinds of fungus. Essentially, moulds are living organisms (plants) that make spores instead of seeds which float in the air like pollen. Spores are regenerative cells surrounded by a very tough coating that can survive detergents, chemicals, bleach and extreme temperatures. Mould spores are microscopic in size, typically requiring 600X magnification to identify. It is has been said that 200,000 mould spores can fit on the head of a pin. A visible patch of mould the size of a coin can represent billions of spores. Moulds reproduce by releasing spores. When mould spores colonize (settle) on a surface they can grow and spread rapidly, giving off a variety of odours and exhibiting hundreds of different colours and textures.
Types of Mould
There are approximately 200,000 types of mould, of which less than 100,000 have been named. Approximately 1,000 types of mould are found indoors and less than 80 moulds are suspected of causing some form of illness, and only a few of them are considered toxic.
Moulds are organized into three groups according to human responses; Allergenic, Pathogenic, and Toxigenic.
Allergenic moulds do not usually produce life-threatening health effects and primarily affect those who are already allergic or asthmatic. The human system responses to allergenic moulds tend to be relatively mild depending on individual sensitivities. Typical symptoms include scratchy throats, eye and nose irritations and rashes.
Pathogenic moulds usually produce some type of infection. They can cause serious health effects in persons with suppressed immune systems. Healthy people can usually resist infection by these organisms regardless of dose. In some cases, high exposure may cause hypersensitivity pneumonitis (an acute response to exposure to an organism).
Mycotoxins can cause serious health effects in almost anybody. These agents have toxic effects ranging from short-term irritation to immunosuppression and possibly cancer.
The most common types of mould found indoors include:
Alternaria grows in damp spaces, like showers and under sinks with leaky pipes. It sometimes grows in carpets that have been damp for a while, too. However, it can grow in areas with only minimal moisture. It can be found outdoors as well as indoors and spreads easily. It can cause allergy symptoms and the development of asthma. Elderly people, children, those with respiratory problems and those with immunosuppression (such as HIV + people or those undergoing chemotherapy) are at greater risk for health problems from alternaria.
Cladosporium grows on both wooden surfaces and fabrics, like carpeting. It can also be found outdoors, where it mainly grows on plant material. It typically enters the house through HVAC systems or simply through open windows or doorways. Cladosporium can cause problems with your skin and nails as well as respiratory problems. It can lead to all the usual mould-related respiratory problems, though, like upper respiratory infections, allergic reactions, itchy eyes, coughing, sneezing and runny nose.
Penicillium is frequently found in things like insulation, carpeting, wallpaper and rotting fabrics (things like old mattresses, couch cushions, etc.). It’s known to spread rapidly and easily from one place to another. It’s one of the most common of all the different types of mould, and is actually the substance from which the antibiotic penicillin is made. Its medicinal use does not mean it’s harmless, though. Exposure to penicillium mould can lead to chronic sinus infections, allergy symptoms and an inflammation of the lungs.
Stachybotrys Chartarum, sometimes referred to as “black mould” due to its slimy black appearance, typically grows in places with continuous moisture, like around a leaky pipe or in air conditioning ducts where there is a great deal of condensation. It can spread to other areas, though. Of all the different types of mould, stachybotrys chartarum may be associated with the most health problems. Exposure can lead to chronic sinus infections, asthma attacks, allergy symptoms, depression and fatigue.
In addition, the following moulds can also be found indoors:
A zygomycete fungus which is considered common to the indoor environment. Reported to be allergenic. May cause mucorosis in immune compromised individuals. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites. Absidia cormbifera has been an invasive infection agent in AIDS and neutropenic patients, as well as, agents of bovine mycotic abortions, and feline subcutaneous abscesses. Acremonium species may be confused with Fusarium species that primarily produce microconidia in culture. Fusarium genera are generally much more rapid growers and produce more aerial mycelium.
Acremonium sp (Cephalosporium sp.)
Reported to be allergenic. Can produce a trichothecene toxin which is toxic if ingested. Can cause nausea, vomiting, and diarrhea. Asexual state of Emericellopsis sp., Chaetomium sp., and Nectripsis sp. It can produce mycetomas, infections of the nails, onychomycosis, corneal ulcers, eumycotic mycetoma, endophthalmitis, meningitis, and endocarditis.
Extremely widespread and ubiquitous. Outdoors it may be isolated from samples of soil, seeds, and plants. It is commonly found in outdoor samples. It is often found in carpets, textiles, and on horizontal surfaces in building interiors. Often found on window frames. The species Alternaria alternata is capable of producing tenuazonic acid and other toxic metabolites which may be associated with disease in humans or animals. Alternaria produces large spores having sizes between 20 – 200 microns in length and 7 – 18 microns in width, suggesting that the spores from this fungi are deposited in the nose, mouth, and upper respiratory tract. It may be related to bakers asthma. It has been associated with hypersensitivity pneumoniti, sinusitis, deratomycosis, onychomycosis, subcutaneous phaeohyphomycosis, and invasive infection. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.
Widespread saprophyte on dead plant material, particularly swampy grasses. Should be considered an allergen. This fungus has also been documented in various subcutaneous infections. No toxic related diseases are of record to date.
One of the major classes of fungal organisms. This class contains the the “sac fungi” and yeasts. Some ascomycete spores can be identified by spore morphology, however; some care should be excersised with regard to specific identification. Many ascomycete spores are reported to be allergenic.
A genus of fungi containing approximately 150 recognized species. Members of this genus have been recovered from a variety of habitats, but are especially common as saprophytes on decaying vegetation, soils, stored food, feed products in tropical and subtropical regions. Some species are parasitic on insects, plants and animals, including man. Species within this genus have reported Aw’s (water activities) between 0.75 – 0.82. All of the species contained in this genus should be considered allergenic. Various Aspergillus species are a common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms. Chronic cases may develop pulmonary emphysema. Members of this genus are reported to cause a variety of opportunistic infections of the ears and eyes. Sever pulmonary infections may also occur. Many species produce mycotoxins which may be associated with disease in humans and other animals. Toxin production is dependent on the species or a strain within a species and on the food source for the fungus. Some of these toxins have been found to be carcinogenic in animal species. Several toxins are considered potential human carcinogens.
A cosmopolitan fungus with the main habitat apparently on the aerial parts of plants. Frequently found in moist environments. This fungus should be considered allergenic. This species has been associated with deratitis, peritonitis, pulmaonary infection, and invasive disease in AIDS patients. Probably acquired by traumatic implantation. May be recovered as a contaminant from human cutaneous sites. No toxic diseases have been documented to date.
One of the major classes of fungal organisms. This class contains the mushrooms, shelf fungi, puffballs, and a variety of other macrofungi. It is extremely difficult to identify a specific genera of mushrooms by using standard culture plate techniques. Some basidiomycete spores can be identified by spore morphology, however; some care should be exercised with regard to specific identification. Many basidiomycete spores are reported to be allergenic.
A widespread fungus that is most frequently associated with grasses, plant material, decaying food, and soil. It is common to both indoor and outdoor environments. Older obsolete names include Drechslera and Helminthosporium. This fungus produces large spores which would be expected to be deposited in the upper respiratory tract. Various species of this fungus can produce the mycotoxin – sterigmatocystin which has been shown to produce liver and kidney damage when ingested by laboratory animals.
This genus contains a variety of organisms that have been isolated from the environment, as well as human skin and mucous membranes.
Large ascomycetous fungus producing perithecia. It is found on a variety of substrates containing cellulose including paper and plant compost. It can be readily found on the damp or water damaged paper in sheetrock.
Widespread, common in the soil and on plants. Rare agents of onychomycosis, skin lesions, endocarditis, and uncommon agents of the pulmonary mycosis adiaspiromycosis. No toxic diseases have been documented to date.
Cladosporium sp (Hormodendrum sp)
Aw (water activity) in the range of 0.84 to 0.88. Most commonly identified outdoor fungus. The outdoor numbers are reduced in the winter. The numbers are often high in the summer. Often found indoors in numbers less than outdoor numbers. It is a common allergen. Indoor Cladosporium sp. may be different than the species identified outdoors. It is commonly found on the surface of fiberglass duct liner in the interior of supply ducts. A wide variety of plants are food sources for this fungus. It is found on dead plants, woody plants, food, straw, soil, paint and textiles. It can cause mycosis. Produces greater than 10 antigens. Antigens in commercial extracts are of variable quality and may degrade within weeks of preparation. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.
Reported to be allergenic. It may cause corneal infections, mycetoma and infections in immune compromised hosts.
Conidia (spores) dimensions 40-120 x 17-28 microns. Found on grasses, grains and decaying food. It can occasionally cause a corneal infection of the eye.
Conidia (spores) dimensions 15-25 microns. A common allergen. It is found in plants, soil, grains, textiles, and paper products.
Aw (water activity) 0.90. A common soil fungus. It is found on a wide range of plants. It is often found in humidifiers. Several species in this genus can produce potent trichothecene toxins (5, 27). The trichothecene (scirpene) toxin targets the following systems: circulatory, alimentary, skin, and nervous. Produces vomitoxin on grains during unusually damp growing conditions. Symptoms may occur either through ingestion of contaminated grains or possibly inhalation of spores. The genera can produce hemorrhagic syndrome in humans (alimentary toxic aleukia). This is characterized by nausea, vomiting, diarrhea, dermatitis, and extensive internal bleeding. Reported to be allergenic. Frequently involved in eye, skin and nail infections.
Aw (water activity) 0.90. Conidia (spores) dimensions 6-12 x 3-6 microns. Aw (water activity) 0.90. A common contaminant of grains, fruits, dairy products, paper, textiles, soil and water, and often present as part of the normal human flora. The species Geotrichum candidum can cause a secondary infection (geotrichosis) in association with tuberculosis. This rare disease can cause lesions of the skin, bronchi, mouth, lung, and intestine.
Often found in soil, dead plant material, horse dung, fruits, and fruit juice. It is also found in leather, meat, dairy products, animal hair, and jute. A Zygomycetes fungus which may be allergenic (skin and bronchial tests) (7, 17). This organism and other Zygomycetes will grow rapidly on most fungal media. May cause mucorosis in immune compromised individuals. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.
Reported to be allergenic.
Commonly found in soil and dust, less frequently in air. P. variotii can cause paecilomycosis. Linked to wood-trimmers disease and humidifier associated illnesses. They are reported to allergenic. Some members of this genus are reported to cause pneumonia. It may produce arsine gas if growing on arsenic substrate. This can occur on wallpapers covered with paris green.
This fungi is found in soil, textiles, decaying plants, manure, and paper.
Aw (water activity) 0.78 – 0.88. A wide number of organisms have placed in this genera. Identification to species is difficult. Often found in aerosol samples. Commonly found in soil, food, cellulose, and grains (17, 5). It is also found in paint and compost piles. It may cause hypersensitivity pneumonitis and allergic alveolitis in susceptible individuals. It is reported to be allergenic (skin) (7, 17). It is commonly found in carpet, wallpaper, and in interior fiberglass duct insulation (NC). Some species can produce mycotoxins. A common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.
A common indoor air allergen. It is similar to the early stages of growth of Chaetomium sp. The species are isolated from soil and associated plants (particularly potatoes). Produces pink and purple spots on painted walls (3, 17). It may have antigens which cross-react with those of Alternaria sp. It will grow on butter, paint, cement, and rubber. It may cause phaeohyphomycosis, a systematic or subcutaneous disease.
Grows on dead grass in pastures. Causes facial eczema in ruminants.
The Zygomycetous fungus is reported to be allergenic. It may cause mucorosis in immune compromised individuals. It occupies a biological niche similar to Mucor sp. It is often linked to occupational allergy. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.
The Zygomycetous fungus is reported to be allergenic. It may cause mucorosis in immune-compromised individuals. It occupies a biological niche similar to Mucor sp. It is often linked to occupational allergy. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.
A reddish yeast typically found in moist environments such as carpeting, cooling coils, and drain pans. In some countries it is the most common yeast genus identified in indoor air. This yeast has been reported to be allergenic. Positive skin tests have been reported. It has colonized in terminally ill patients.
Reported to be allergenic. See also Sporothrix sp. as there is some taxonomic confusion between these two genera. This genera does not cause sporotrichosis.
Aw (water activity) – 0.94, optimum Aw (water activity) – >0.98. Several strains of this fungus (S. atra, S. chartarum and S. alternans are synonymous) may produce a trichothecene mycotoxin- Satratoxin H – which is poisonous by inhalation. The toxins are present on the fungal spores. This is a slow growing fungus on media. It does not compete well with other rapidly growing fungi. The dark coloured fungi grows on building material with a high cellulose content and a low nitrogen content. Areas with relative humidity above 55% and are subject to temperature fluctuations are ideal for toxin production. Individuals with chronic exposure to the toxin produced by this fungus reported cold and flu symptoms, sore throats, diarrhea, headaches, fatigue, dermatitis, intermittent local hair loss, and generalized malaise. The toxins produced by this fungus will suppress the immune system affecting the lymphoid tissue and the bone marrow. Animals injected with the toxin from this fungus exhibited the following symptoms: necrosis and hemorrhage within the brain, thymus, spleen, intestine, lung, heart, lymph node, liver, and kidney. The mycotoxin is also reported to be a liver and kidney carcinogen. Affects by absorption of the toxin in the human lung are known as pneumomycosis. This organism is rarely found in outdoor samples. It is usually difficult to find in indoor air samples unless it is physically disturbed. The spores are in a gelatinous mass. Appropriate media for the growth of this organism will have a high cellulose content and a low nitrogen content. The spores will die readily after release. The dead spores are still allergenic and toxigenic. Percutaneous absorption has caused mild symptoms.
Reported to be allergenic. Isolated from dead plants and cellulose materials.
Can cause a respiratory infection characterized by a solid fungal ball.
It is commonly found in soil, dead trees, pine needles, paper, and unglazed ceramics. It often will grow on other fungi. It produces antibiotics which are toxic to humans. It has been reported to be allergenic (7, 17). It readily degrades cellulose.
Can cause ring worm, athlete’s foot, skin, nail, beard, and scalp (5, 6). Reported to be allergenic. Found on soil and skin.
Has an Aw (water activity) of 0.89. Isolated from dead plants and cellulose materials. Found on textiles.
Conidia (spores) dimensions 2.3-10 x 1-2.6 microns. Found in decaying vegetation, on straw, soil, and arthropods. A rare cause of corneal infections.
Has an Aw (water activity) of 0.75. Conidia (spores) dimensions 2.5-3.5 microns. Found in sugary foods, salted meats, dairy products, textiles, soil, hay, and fruits.
Various yeasts are commonly identified on air samples. Some yeasts are reported to be allergenic. They may cause problems if a person has had previous exposure and developed hypersensitivity. Yeasts may be allergenic to susceptible individuals when present in sufficient concentrations.
Mold is a form of fungus that grows both indoors and outdoors and thrives in warm, damp, and humid environments. There are over a thousand different varieties of indoor mold, and the good news is that the presence of a moderate amount of mold in your home is generally not harmful to your health. Most health problems related to mold exposure arise only when there is a build-up of high concentrations of mold for some reason.
Mold spreads by generating spores, and like so many nuisances in life, mold spores are able to survive for long periods even in harsh, dry environments in which mold itself could not grow — which is one of the things that makes mold so hard to eliminate. Mold spores are invisible to the eye and can become airborne — an important consideration during efforts to clean up and eliminate a mold infestation.