Health Classification of Mold

When it comes to human health, mold is often classified by the commons affects a particular mold has on the health of humans exposed to it. These categories are: Allergenic, Toxigenic and Infectious. Some mold fall into more than one category.

– Is the most common effect and can range from hay fever and asthma all the way to very particular reactions and diseases in certain organs or tissues. Hay fever like symptoms are probably the most common health effects attributed to mold in indoor environments.

Major indoor allergenic mold include: Cladosporium, Alternaria, Ulocladium

– Mold in this category can manifest themselves in a very wide variety of ways. Most research up to now has been directed at effects that have to do with ingestion (such as by eating contaminated grain), and comparatively little has been studied about inhaled effects. A particular species of Stachybotrys (S. chartarum) produces a toxin that has been linked to bleeding lung deaths of ten infants in Cleveland. A host of other severe health effects has since been attributed to this toxin, and currently this and very similar toxins produced by other molds (Memnoniella and Trichoderma) are where much interest has been directed in terms of inhaled toxins.

Major indoor toxin producing mold: Stachybotrys, Memnoniella, Trichoderma, Aspergillus, Penicillium, Fusarium

– Are potentially the most dangerous and deadly of mold health effects, but mold in general has an inherently difficult time infecting an uncompromised immune system. Many molds won’t even grow at normal body temperature. While these infections are rare, infections in compromised individuals are much more common and can be very dangerous and problematic do to the lack of treatment options. Compromised individuals include those whose immune system systems are weakened such as (but not limited to) those with AIDS, certain cancers, the very old, the very young, and those undergoing certain drug therapies.

Major infectious indoor mold: Aspergillus, Fusarium, Zygomycetes (includes Mucor / Rhizopus)

Notes on Identification and Classification

Certain molds, particularly Chaetomium and Arthrinium (and to a lesser degree Pithomyces, Stemphyllium, Torula, and Ulocladium), are important as warning markers. These molds can grow under the same conditions as Stachybotrys, and when they are detected in amplified quantities in the indoor air it might be a sign that conditions exist conducive to Stachybotrys growth.

Large classes of molds that are reported such as “Ascospores” and “Myxomycetes / Rust / Smut” are generally used to indicate common “outdoor” or plant molds that are currently believed to have little effect on human health. “Basidiospores” are similar, but they are of a little more concern when observed indoors (due to more frequent allergenic properties and as an indicator of water damage or an overly humid environment).


Disclaimer: Diagnosis of a particular health effect should be left to a medical professional. Health effects of mold, in general, are not thoroughly studied, and dosage, exposure, and sensitivity thresholds are not well known and can van depending on various conditions and on the health and body of particular individuals. Effects will also vary from species to species within a particular mold genus. Many of the negative effects of mold that have been observed recently are the result of modern building design and its lacking adequate ventilation (which can vary from room to room).


Common Types of Mold

Below is a list of the most common types of mold found in the United States. This is not a complete list of mold species, nor all of the types that are present in the US. They are the most dominant types found in nature and in properties.

(bow-vary-uh) – contaminant, known to be pathogenic in animals and insects. Rarely involved in human infection.

Botrytis (bow-try-tus) – contaminant, parasitic on plants and fruits. Rarely involved in human infection, but it is reported to be allergenic.

Chaetomium (k-toe-me-um) – contaminant, rarely involved in systemic and cutaneous disease and sometimes reported to be allergenic. Some species can produce toxins, and there is some research interest on whether these toxins can cause cancer. Primary IAQ importance is currently related to that it will grow in the same conditions as Stachybotrys (wet cellulose) and amplified amounts in indoor air could be a warning that conditions do exist for Stachybotrys growth. Many times on damp sheetrock paper, colonies of Chaetomium and Stachybotrys will be growing on top of one another or side by side (this can also be an important consideration when doing tape lifts of sheetrock because most of the time the colonies are not distinguishable by the naked eye – the small area that is sampled might be a pure colony of just Chaetomium even though numerous colonies of Stachybotrys might exist.)

Chrysonilia (kris -o-nil-ee-a) – contaminant, brightly colored, fast growing mold, which spreads easily through contamination. Health effects are not yet known. It is found in soil, breads, and contaminated laboratory cultures.

Cladosporium (clad-oh-spore-ee-um) – common allergen / contaminant / very rarely pathogenic, found everywhere, many times the most common and numerous mold found in outdoor air. Indoor concentrations are usually not as high, but it is an important airborne allergen and common agent for hay fever, asthma, and other allergy related symptoms. Chronic cases may develop emphysema. It can thrive in various indoor environments, appearing light green to black.

Curvularia (curve-you-lair’-ee-uh) – contaminant / opportunistic pathogen, found in air, soil and textiles. Reported to be allergenic. Rare infections of corneas, nails, and sinuses, primarily in immunocompromised individuals.

Dematiaceous mold (dim-ah-tie-ay-shush) – a very generic morphological description used for various brown molds (mainly on tape-lifts) that cannot be identified because of undistinguishable spores \ structures or because of too much environmental damage to the mold structures. This identification generally excludes many of the common toxic and more infectious molds found indoors, but on some occasions when the mold is very weathered or damaged, this category could potentially include mold from Alternaria, Epicoccum, Ulocladium or others.

Drechslera (dresh-lair’-uh) / Bipolaris (by-pole-air’-us) – contaminant/opportunistic pathogen, found in soil. Allergenic and the most common agent for allergic fungal sinusitis. Various but uncommon infections of the eye, nose, lungs and skin.

Epicoccum (epp-ee-cock’-um) – contaminant / opportunistic pathogen, found in soil, air, water and rotting vegetation and can be commonly found in outdoor air. It is a common allergen, and rarely it can cause an infection in the skin.

Exophiala (ex-oh-fy’-all-uh) – contaminant / opportunistic pathogen. Commonly found in soil, decaying wood, and various other wet materials because it thrives in water laden environments. Indoors it can be found in air conditioning systems, humidifiers, and other surfaces in frequent contact with moisture. Some species linked to occasional skin infections and various other subcutaneous lesions. Allergenic effects and toxicity are not well studied.

Fusarium (few-sarh-ee-um) – contaminant / opportunistic pathogen, found on fruit, grains and is common in soil. Indoors it sometimes contaminates humidifiers. Associated with as eye and various other infections in immunocompromised individuals and particularly burn patients. Produces a variety of toxins mainly important when ingested, particularly thru contaminated grain products.

Geotrichum (gee-oh-trick-um) – contaminant, commonly found in dairy products and found as a normal part of human flora. There are some reports of infection in compromised hosts, but most of these are not well documented.

Gliocladium (glee-oh-clay’-dee-um) – contaminant, found widespread in soil and decaying vegetation. Similar to Pencillium, but there are no reports of infections in humans or animal. There are some reports of allergies.

Memnoniella (mem-non-ee-el-la) – contaminant, found most often with Stachybotrys on wet cellulose. Forms in chains, but it is very similar to Stachybotrys and sometimes is considered to be in the Stachybotrys family. Certain species do produce toxins very similar to the ones produced by Stachybotrys chartarum and many consider the IAQ importance of Memnoniella to be on par with Stachybotrys. Allergenic and infectious properties are not well studied.

Mucor (mhew’core) – contaminant / opportunistic pathogen, found in soil, decaying vegetation, and animal dung. It is common to find some spores in normal house dust. It’s a minor allergen and can cause Zygomycoses and lung infections in compromised individuals.

Myxomycete (mix-oh’-my-seat) / Rust / Smut – general category for commonly found genera usually associated with living and decaying plants as well as decaying wood. Sometimes can be found indoors. Some allergenic properties reported, but generally pose no health concerns to humans or animals.

Paecilomyces (pay-sill-oh-my-sees) – contaminant / opportunistic pathogen, found worldwide in soil and decaying vegetation, associated with pulmonary and sinus infections in those who had organ transplants, as well as inflammation of the cornea. Some reports of allergies, humidifier associated illnesses, and pneumonia.

Penicillium (pen-uh-sill’-ee-um) – contaminant / opportunistic pathogen, one of the most common genera found worldwide in soil and decaying vegetation and indoors in dust, food, and various building materials. Common bread mold is a species of Penicillium. Spores usually cannot be distinguished from Aspergillus on non-cultured samples (like tape-lifts and air-o-cells). It is reported to be allergenic, to cause certain infections in compromised individuals, and some species do produce toxins unhealthy to humans.

Phoma (fo’-mah) – contaminant / opportunistic pathogen, found on plant material and soil. Reported to be a common allergen found indoors on painted walls (including the shower) and on a variety of other surfaces including cement, rubber, and butter. Some believe its effect on indoor air is not that significant because its spores do not travel well via air currents. Some species are linked to occasional eye, skin, and subcutaneous infections.

Pithomyces (pith-oh-my-sees) – contaminant, found on decaying plants, especially leaves and grasses. Rarely found indoors, but it can grow on paper. No reports of allergies or infections, but some species produce a toxin that causes facial eczema in sheep.

Rhizopus (rye-zo-puss) – contaminant / opportunistic pathogen, found in soil, decaying vegetation, and animal dung. It is reported to be allergenic, and some consider it a major allergen often linked to occupational allergy. It can cause Zygomycoses and other infections in compromised individuals.

Scopulariopsis (scope-you-lair-ee-op’-siss) – contaminant / opportunistic pathogen, found world wide in soil and decaying vegetation and often be found indoors on various materials. Usually is only a contaminant but some reports of allergies and an as agent for certain types of nail infections.

Stachybotrys (stack-ee-bought-ris) – contaminant, found indoors primarily on wet cellulose containing materials. It is the “toxic black mold” that has garnered much media attention. Stachybotrys is sometimes difficult to detect indoors because many times it will grow unseen on the back of walls or in the wall cavity with little disturbance that would cause it to be detected. This is potentially also when it is of most health concern: when it covers entire wall areas and constantly produces toxins undetected. Areas with relative humidity of 55% that 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 including sore throats, diarrhea, headaches, fatigue, dermatitis, intermittent hair loss and generalized malaise.  Exposure to the toxin may also exacerbate allergic type symptoms, especially in persons who have a history of hypersensitivity diseases such as asthma, pneumonitis and severe sinusitis.  Allergic rhinitis and conjunctivitis may be other conditions exhibited.  The toxin produced by this fungus may suppress the immune system.   Species of Stachybotrys earned considerable notoriety in recent years due to their production of potent toxins in indoor environments.   They have been linked to some cases of infant deaths in moldy buildings. A host of other toxic reactions in humans are also linked to it. Symptoms usually disappear after all contaminated materials are removed.  This mold is rarely pathogenic for humans.   Ref:  Jong and Davis, 1976.

Stemphylium (stem-fill-ee-um) – contaminant, reported to be an allergen. Rarely grows indoors, but can grow on cellulose materials like paper.

Syncephalastrum (sin-sef-al-os-trum) – primarily a contaminant, often found in the soil of warm, moist climates. Very rarely involved in infections.

Taeniolella (tan-o-ee-el-la) – contaminant, little is known concerning allergenic properties or toxicity. Primarily grows on wood.

Trichoderma (trick-oh-derm-uh) – contaminant / opportunistic pathogen, found in soil. Can be found indoors on cellulose materials like paper and in kitchens on various ceramic items. Human infections are rare but some have been reported in immune suppressed patients. It is reported to be allergenic though some report these effects to be rare. It can produce toxins very similar to those produced by Stachybotrys chartarum, and because of this it is considered an important mold in IAQ investigations.

Torula (tore-you-law) – primarily a contaminant, but it is reported to be allergenic. Can be found indoors on cellulose containing material.

Ulocladium (you-low-clay-dee-um) – contaminant, found everywhere. Can grow indoors on various materials including paper, but requires more water than some other molds. It is reported to be a major allergen.

Verticillium (ver-ti-sill-ee-um) – primarily a contaminant found in soil and decaying plants. Health effects are not well studied. A few sources report it as a very rare cause of cornea infections.

Zygomycetes (zy-go-my-seets) – large class of genera that includes Mucor and Rhizopus. Some species may cause infections and zygomycosis in compromised individuals, and some species may be major allergens. The category Zygomycete on reports is a morphological identification when the particular genus cannot be identified. Particularly on non-cultured samples such as tape-lifts and air-o-cells, many Zygomycete spores and even other clear round spores are indistinguishable by genus.