Common Molds

Alternaria sp.

Alternaria is a very common fungal saprophyte found on decaying wood, in composts, on plants and food, and in different types of soil. Its distribution is worldwide and is frequently found in outside air, where in temperate climates, the conidia (spore) levels reach their peak in late summer. Indoors it can be found in dust and carpets, on damp spots around showers and window frames, and virtually any area where condensation exists.

The ubiquitous and common Alternaria is an important fungal allergen. Allergies to Alternaria will most often cause an immediate mediated allergic response, however, there have been documented cases of hypersensitivity pneumonitis to airborne exposure of Alternaria spores. Serious infection associated with Alternaria is rare. Alternaria mycotoxins have not been the subject of much investigation although they are produced.

Aspergillus sp.

There are more than 160 species of Aspergillus, 16 of which have been documented as etiological agents of human disease. They are among the most common groups of environmental fungi. Many species are isolated from a variety of substrates, including grains, nuts, cotton, organic debris and water damaged, organic building materials. The most frequently encountered opportunistic Aspergillus pathogen is A. fumigatus and is seen most abundantly in decomposing organic materials. Aspergillus fumigatus and A. niger have been identified as the more harmful species of the Aspergillus group.

Aspergillus is considered a common environmental mold that can pose health risks when it is present in elevated levels. Health problems due to Aspergillus exposure may include headaches, eye and skin irritation, asthma, aggravation of existing respiratory conditions, other typical allergic symptoms, and hypersensitivity pneumonitis. Hypersensitivity and allergic responses can be triggered by minimal exposure and especially in people who have an existing sensitivity to mold allergens and toxins or who have compromised or suppressed immune function. Aspergillus can proliferate successfully indoors when conditions become favorable resulting in an increase in the number of spores, and therefore, mycotoxin concentrations that can be harmful.

Aureobasidium pullulans.

Aureobasidium is one of several “black yeasts” so called because of its slimy black appearance in cultures. It is a common saprophyte with worldwide distribution and is frequently isolated from soils. During autumn, Aureobasidium colonizes the surface of the leaves of many types of trees, producing pectinases that break down the cell walls. The initial decomposition of leaves is generally caused by Aureobasidium paving the way for other molds to further breakdown the leaves. Aureobasidium is a known allergen, however, not much information is available on this mold to date.

Chaetomium sp.

Chaetomium is a common mold with a ubiquitous distribution of the over 80 species currently described. Commonly found on deteriorating wood products, Chaetomium frequently emits a musty odor. It is frequently found on water-damaged drywall and other lower cost construction products often used in the United Sates. Chaetomium is found on a variety of substrates containing cellulose including paper and plant compost. Several species have been reported to play a major role in the decomposition of cellulose-made materials. These fungi are able to dissolve the cellulose fibers in cotton and paper and thus cause the materials to disintegrate. The decomposition process is especially rapid under moist conditions.

Health effects related to Chaetomium have not been well studied however the mold can produce some compounds that have been identified as health hazards. This fungus is reported to be allergenic and toxic and can cause typical allergic and toxic responses in sensitive individuals. Unfortunately, little data is available regarding inhalation of components of Chaetomium.

Cladosporium sp.

Cladosporium is an extremely common mold found in temperate climates. The spores readily become airborne and are transported over long distances. The high season for Cladosporium is typically late summer and autumn while the low season is typically winter and early spring. Cladosporium has been isolated from many different types of soil and plant litter; enzymes produce by the mold breakdown cellulose, pectin, and lignin that are major components of leaf litter.

Inside, Cladosporium can be found in dirty refrigerators, in condensation reservoirs, on moist window frames, and pretty much on any moist, porous surface. Cladosporium often discolors interior paint, paper, or textiles stored in humid environments.

The ability for Cladosporium to rapidly and heavily sporulate makes this mold a common airway allergen associated with asthma and hay fever. Cladosporium may cause more serious illnesses in individuals with suppressed immune function.

Paecilomyces sp.

Paecilomyces has been isolated from jute fibers, paper, PVC timer (oak wood) optical lenses, leather, photographic paper, cigar tobacco, grapes, bottled fruit and fruit juice undergoing pasteurization. Type I allergies (hay fever, asthma) and Type III hypersensitivity pneumonitis have been associated with Paecilomyces exposure. Species of the mold genus Paecilomyces are seldom associated with serious human infection.

Penicillium sp.

The spores of Penicillium contain mycotoxins responsible for causing a variety of allergy symptoms and illnesses. Mycotoxins are chemicals produced by fungi that are most concentrated in the spores but are also present in actively growing mold filaments. Under normal circumstances, the indoor concentration of spores is generally low enough to not provoke an immune response except in those people who are sensitive to the specific mycotoxins or have compromised immune systems. Mycotoxins can cause a variety of short-term, as well as long-term, illnesses. Symptoms due to mycotoxin exposure include dermatitis, cold and flu symptoms, sore throat, headache, fatigue, diarrhea, and impaired or altered immune function, which may lead to opportunistic infections.

Stachybotrys atra

Stachybotrys is described as an indicator mold and when identified in either air or bulk sampling “may signal moisture presence or a potential for health problems” (Macher et al., 1999). Stachybotrys is generally found on materials with high cellulose content (such as wallboard and ceiling tiles) that become chronically moist or water damaged from excessive relative humidity, pipe or roof leaks, condensation, or flooding. Several toxins are produced by Stachybotrys and are known to be toxic to humans exposed to significant quantities. If Stachybotrys spores are released into the air, there is a potential for allergic, respiratory, or immunological symptoms to develop or become exacerbated. These conditions include asthma, hypersensitivity pneumonitis, allergic rhinitis, dermatitis, sinusitis, and conjunctivitis (New York City Department of Health, 1993).