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  • Mold

Environmental Health & Safety

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  • Mold

    Molds are a subdivision of fungi which represent a very diverse group of life-forms on earth. They are a natural part of our environment in virtually all areas of the planet. For years fungi were categorized as plants, but scientific studies revealed properties that notably distinguish fungi from plants and therefore, these organisms were given their own kingdom in the classifications of life...Kingdom Fungi. 

    Mother Nature's Recycling Center

    The primary purpose of fungi is to break-down organic matter and unshackle nutrients. Together with bacteria, fungi decompose the majority of dead organic matter on our planet. 

    Kingdom Fungi

    Classifications within Kingdom Fungi get very complex and are beyond the scope this general overview. In lay terms, organisms are grouped based on their familiar descriptions including molds, yeasts, mildew, rusts, smuts, mushrooms, and puffballs.

    In our simplified view:

    • Molds are microscopic multicellular organisms that grow as long, tangled strands and form visible colonies. Reproduction is primarily a function of spore development and dispersal.
    • Yeasts are microscopic unicellular organisms whose colonies appear as groups of berries.
    • Mildew, rusts, and smuts are primarily associated with plants.
    • Mushrooms, toadstools and puffballs are visible, fleshy organisms. 

    It's Only Mildew...

    Many people refer to 'mildew' as the commonly occurring fungi that grow on damp clothing or bath tiles as if it is a more friendly organism. In reality, such growth is typically a filamentous mold of the types likely found on water-damaged building materials. On this site, the term 'mildew' is used to describe types of fungi more commonly associated with living plants (i.e. powdery mildew). 

    Saprobes, Parasites and Pathogens

    Most fungi feed on dead organic matter (a saprobe), however, some types are parasitic and feed on living things. Pathogenic (disease causing) fungi are known to cause adverse health in animals and humans. 

    A Note on Conventions

    Molds are named and catalogued in accordance with the scientific classifications of Taxonomy. Mold names are usually presented as a genus (i.e. Aspergillus) or in the genus-species format (i.e. Aspergillus flavus). Unfortunately, many Latin names are used which makes for some tongue twisters.

    The genus is typically capitalized and the species is written lower case. The convention of Aspergillus spp. is used to indicate all species of the Aspergillus genera and Aspergillus sp. is used to indicate one species. The abbreviated convention of A. flavus represents the full genus-species name of Aspergillus flavus. Note that when written, mold names are typically italicized or underlined.

    Taxonomic Ranking

    • Kingdom
    • Phylum (Division)
    • Class
    • Order
    • Family
    • Genus
    • Species


    Mycology is the study of fungi and some consider a mycologist to be part biologist, chemist, naturalist, cryptologist, and wizard.

    Note that the study of fungi is far from complete. Mycologists have described an estimated 80,000 species of fungi and many believe that this is only a fraction of what remains to be discovered. Estimates of 1.5 million species and variants have been suggested.

    To understand the complexities facing these professionals, jot down the names of the first 80,000 people you know and describe their behavior in various settings. (Yes, there is probably even a fungus that acts like that relative no one speaks about.) 

  • It's not easy to simplify the growth requirements of 80,000 complex organisms, but suffice to say, our indoor environments provide suitable conditions for many types of fungi.

    Granted, there are fungal organisms that require specific light/dark cycles, temperature, nitrogen/oxygen levels, nutritional constituents, moisture levels, etc. for optimum growth and reproduction, however, our focus is on the types of fungi likely to occur in indoor environments.

    For many of these organisms growth can be simplified to three significant factors:

    • Mold Spores
    • Organic Food
    • Water

    Envirochex uses the 'Mold Growth Triangle' to illustrate this relationship and serve as a simplified overview of growth requirements. When a mold spore locates a suitable food source with sufficient moisture, growth occurs. Simple as that.

    Growth starts when the Mold Triangle is formed...

    Spores provided with sufficient moisture and suitable food form microscopic, branched, thread-like filaments called hyphae (hi-fee). Continued hyphal growth forms a mass called a mycelium (my-sill-ee-um) which often becomes visible within 24-48 hours.

    As the organism grows, reproductive spores are formed and released as part of it's continuing life cycle.
    Understanding the Mold Growth Triangle provides insight into methods of control that result in elimination of inappropriate indoor growth. 

    Most molds reproduce by forming spores that disperse into the air in search of more food and moisture (a reproductive activity similar to seed dispersal from plants). Due to the diversity of mold in our environment, outdoor air normally always contains some level of these airborne mold spores.

    A few types of spores are visible and anyone who has disrupted a puffball has witnessed millions of spores being released into the atmosphere. However, most filamentous mold spores are microscopic and therefore, invisible to the naked eye.

    It is not uncommon to find hundreds or even thousands of mold spores per cubic foot of outdoor air. Some mold types, like Cladosporium, produce light and buoyant spores that aerosolize easily which is one factor in Cladosporium being frequently recovered in outdoor air tests.

    Other types of mold, like Stachybotrys, do not easily go airborne and therefore, their spores are not frequently recovered in outdoor air tests. When actively growing, Stachybotrys spores are typically a wet, sticky mass that is not easily aerosolized. Some believe this organism's spores are like a cocklebur that hitchhikes on insects and rodents rather than traveling by air. 

    Spore Viability

    Not all spores produced by the organism are capable of growing a new colony. Microbiologists use the terms viable and non-viable to indicate their ability to reproduce and in lay terms, these spores are considered alive or dead. Numerous factors (i.e. spore desiccation or other physical damage, etc.) influence a spore's ability to grow and comparative testing has shown a large percentage of airborne spores to be non-viable.

    It is very important to recognize that spores retain their adverse health characteristics regardless of their ability to reproduce. In other words, non-viable spores are still allergens, contain toxins, etc. This trait not only has significance on exposure to molds, but also greatly influences testing methods.  

    Size Range of Spores

    Things in the mold world are very small and dimensions are typically expressed in micrometers or microns (millionths of a meter). Most fungal spores range from 1 to 100 microns in size with many types between 2 and 20 microns. People with good vision may see 80-100 micron particles unaided, but below that range, magnification is generally necessary. To put things in perspective, you could place over 20 million five micron spores on a postage stamp. A wonderful animation to depict sizes in the micron range can be viewed at the "How Big is..." page from CellsAlive!. This small size has numerous impacts on dealing with mold. They are so tiny that they infiltrate our environments with air and they are essentially invisible so cleaning them up without special equipment and procedures is next to impossible. (It's tough to clean up things you can't see!) 

    Spore Infiltration

    Since outdoor air normally contains some quantity of mold spores, infiltration of airborne mold into living and working environments occurs naturally. Therefore, even in structures without active mold colonies, the presence of airborne fungal materials is probable unless specialized air filtering systems are employed (i.e. clean rooms).

    There is little we can do to stop nature's production of airborne mold spores, however, we can prevent mold from growing indoors. When these organisms are allowed to grow in a closed indoor environment, they can release millions of spores causing indoor levels to reach concentrations that are hundreds of times higher than outdoors...levels that can be detrimental to even healthy people.

    Airborne mold spores are particles and generally settle out with time but they can be disrupted and re-aerosolized. They may also just sit quietly waiting for food and moisture. 

    Natural Airborne Mold Indoors

    Many people have witnessed proof there are natural airborne mold spores indoors. After inadvertently leaving a cup of coffee or food out for a few days, the resulting colony will be visible! 

    Breaking the Mold Triangle - Controlling Spores

    Since mold spores are a natural component in air, they are essentially everywhere. In addition, spores are carried indoors on clothing, articles, pets, etc. Eliminating mold spores from our indoor environments is virtually impossible without extreme measures of air and access control. 

    For molds, the food of choice is organic matter (things that are or once were living). Fungi will consume anything organic, yet many types have selective appetites. Building materials including wood, paper, natural fabrics, leather, and even the starch in wallpaper paste are common examples of dead organic matter preferred by filamentous molds. Grasses, plants, trees, etc. provide examples of living organics for parasitic fungi and animal or human tissue provides a source of living nutrients for many pathogenic fungi. 


    Fungi don't actually "eat" their food, but rather release enzymes to break-down complex organic compounds and absorb nutrients through their cell surfaces. By absorbing nutrients and obtaining carbon and energy necessary for growth from organic sources, fungi are classified as absorptive heterotrophs. During the process of enzyme release and nutrient absorption, molds also produce volatile organic compounds (VOC's). Because they are produced during processes essential to growth, VOC's are termed Primary Metabolites. (Since they are generated from a microbial source, some references list them as microbial VOC's or mVOC's.) Representing a wide range of organic chemicals, VOC's are responsible for the 'moldy/musty' odor associated with fungal growth. 


    Volatile compounds are those that readily evaporate at common room temperatures and pressures.

    To illustrate the concept of volatility, place a drop of rubbing alcohol, water, and a heavy oil on a countertop. The alcohol will evaporate quickly (volatile), the water more slowly (semi-volatile), and the oil is does not evaporate (non-volatile). 

    Substrate and Nutrients

    In most cases, the substrate mold is growing on provides the nutrients, however, in some instances the substrate is simply a foundation. Mold growing on glass, ceramic tile, metals, or other inorganic materials is not obtaining nutrients from these substrates. In these cases, mold is feeding on microscopic organic matter that is on the surface or trapped in tiny pores of the material. Bath-tile mold is an example: Mold is typically consuming organic dust, dirt, debris, skin flakes, body oils, soap scum, etc., and the ceramic tile is simply a foundation for the colony. 

    Breaking the Mold Triangle - Controlling Food

    Eliminating mold growth by controlling food sources is effective in instances where moisture is unavoidable. Using inorganic substrates together with routine cleaning of organic dust/dirt/debris typically controls growth. 

    Water is critical to life-forms, even fungi. Without water, growth and reproduction simply will not occur. The amount of water for optimum growth varies by species and is also influenced by environmental factors such as temperature and the types of nutrients available. Some species can grow at relatively low moisture levels, levels that would not be considered 'wet' in ordinary terms (think of mold growing on bread). Other types of fungi require significant amounts of moisture for optimum growth. 

    Substrate Moisture

    Many materials are porous and will absorb moisture in attempt to reach equilibrium with the source. It is the moisture contained in these materials that allows fungi to survive and grow.

    Dealing with water in liquid form is relatively straight forward. Most everyone recognizes that liquid water moves by forces of gravity causing 'water to run downhill'. But there are other forces which warrant consideration including hydrostatic pressures, capillary actions, and differences in the partial pressures of water vapor. In simple terms, water will move from 'wet towards dry' in an attempt to reach equilibrium between these forces.

    Note that water does not have to be liquid in order to saturate a substrate. Water vapor, a frequent cause of mold growth, is naturally absorbed by most porous materials. Moisture in air (humidity), or water vapor migrating through substrates is often slow developing and may be more difficult to assess. Note that most building materials including concrete, brick, mortar, grout, drywall, wood, etc. are porous and do allow water vapor to pass. 

    Water Activity

    For fungi, the amount of water required is termed the water activity level (Aw); a measure of water in the substrate that an organism can use to support growth. Examples of water activity ranges are shown below. For the types of mold compatible with indoor environments, few are considered capable of growing below Aw = 0.65.
    (Source - ACGIH; Bioaerosols: Assessment and Control; 1999) 

    Scientists establish the water activity values by allowing a growth medium to reach equilibrium at a given relative humidity and observing growth performance for that organism. Therefore, Aw values are equivalent to relative humidity:  

    Aw = %RH/100
    0.65 - 0.80
    0.80 - 0.90
    Some Aspergillus and Penicillium
    Alternaria, Epicoccum, Cladosporium, Aspergillus, etc.
    Fusarium, Rhizopus, Stachybotrys 

    Breaking the Mold Triangle - Controlling Water

    Eliminating mold growth by controlling moisture is considered the key. Take away water and growth simply will not occur. Quick response in drying all materials impacted by plumbing breaks, rain intrusion, etc. and controlling humidity in areas with organic substrates is of paramount importance.  

    Consultation with qualified physicians or other medical experts should be your first step in dealing with any healthcare issue. Symptoms of mold exposure can also be attributed to many other health-related issues and you should always seek the appropriate expert advice. 


    Fungi are a natural part of the environment with outdoor airborne levels subject to numerous ambient conditions. Indoors, airborne levels of mold are primarily influenced by outdoor organisms unless a colonies are established within the structure.

    When indoor areas have mold problems, fungal components can be dramatically elevated over outdoor levels. These elevated levels are generally believed to be the cause of problems with otherwise healthy individuals.

    Unfortunately, healthcare professionals lack comprehensive data on human exposure to all types of fungi. Much of what is known has been extrapolated from observations of animals exposed to mold both in the laboratory and as livestock; or from studies of human exposure in agriculture environments.

    With tens of thousands of species and considerable differences in human sensitivity, the task of qualifying and quantifying health data is substantial. Many molds are classified as opportunistic pathogens meaning the organism is disease-causing given the opportunity to infect the host. Some mycotoxins are documented carcinogens, implying they are suspect cancer-causing agents.

    People suffering from fungal exposures are faced with difficulties. With science lacking definitive answers to many questions, there appears to be no shortage of conflicting opinions. 

    Exposure Routes

    Mold needs access, or what is called a pathway, into the human body in order to be problematic. The most obvious pathways are: Inhalation - Breathing volatile organic compounds (VOC's), spores and/or fragments of mold is generally considered the primary means of exposure to indoor mold. Inhalation exposes the upper and lower respiratory tracts and allows pathways into the blood system via the lungs. Ingestion - Eating food contaminated by mold allows direct exposure of the digestive tract to mold components. Studies of people and livestock that consumed mold-contaminated food has contributed a significant amount of data on infectious and toxic molds. Contact - Touching mold or items contaminated by mold can provide a pathway. Whereas the skin provides good protection, transfer to mucus membranes (e.g. eyes, nose, mouth, etc.) is possible. Openings in the skin (wounds, burns, sores, etc.) can provide a direct pathway into tissue and the bloodstream. Certain types of molds are responsible for infections including ringworm, athletes' foot, jock-itch, and other forms of skin, hair and nail diseases.  

    High Risk Individuals

    Mold exposure is considered especially problematic to infants/children, the elderly, pregnant women, immune-compromised individuals (HIV infection, cancer chemotherapy patients, liver disease, bone-marrow transplants, post-surgical patients, etc.), and persons with unique sensitivities or existing respiratory conditions. Persons with such conditions are advised to be extra careful concerning mold exposure and should not to perform mold cleanup activities without special precautions. 

    Health Issues

    The health affects of mold are generally grouped in the following four categories. Numerous conditions including type and species of mold, exposure levels and methods, environmental conditions, individual sensitivities, etc. are all considered to be factors in the response. Irritation For some people, the "moldy odor" can be irritating to mucous membranes, cause headaches and other symptoms. This odor comes from volatile organic compounds (VOC's) produced by mold as it degrades organic substrates and is generally considered one of the primary causes of irritation. Allergic reactions are typically the most common health problem. Symptoms include respiratory problems and difficulty breathing, nasal and sinus congestion, burning/watery or reddened eyes, dry hacking cough, nose and throat irritation, shortness of breath, skin irritation, headaches, memory problems, mood changes, aches and pains, and possible fever. Infection There are an estimated 100 species of mold known to cause infections in humans and immune suppressed individuals are especially at risk. Infections can be localized or systemic. Aspergillosis is a common fungal infection requiring hospitalization in the U.S. Other fungi can infect hair, skin and nails. Toxicosis Many species of mold produce toxic metabolites called mycotoxins which are believed to be most prevalent in spores (both living and dead spores). Mycotoxins are of special concern since some may present a greater hazard to humans than all other conditions including nerve damage, organ damage, and cancer. Symptoms of toxicosis from mold include cold and flu-like symptoms, headache, nosebleeds, memory problems, fatigue, dermatitis, immune suppression, etc. Reported Symptoms
    The following list represents some of the symptoms reported in literature relative to mold exposure. Other symptoms specific to infectious and/or toxic molds may be experienced. 

    • Respiratory problems
    • Nasal & sinus congestion
    • Burning, watery or reddened eyes
    • Blurry vision or light sensitivity
    • Dry, hacking cough
    • Nose and throat irritation
    • Shortness of breath
    • Skin irritations
    • Headache
    • Memory problems
    • Mood changes
    • Aches & pains
    • Nosebleeds
    • Dermatitis
    • Immune suppression
    • Fatigue
    • Chills/fever 

    As with any health issue, numerous causative agents can elicit similar symptoms; therefore, the presence of such symptoms is not exclusive to mold exposure.  

    If you have concerns about your health and mold, contact your Healthcare Professional.