Indoor Molds


Fate and Transport in the Environment

Methods for Monitoring in the Environment

Exposure Pathways

Methods for Measuring Human Exposure

Strategies for Preventing or Controlling Mold Exposure

Harmful Effects

Absorption, distribution, metabolism, and sites of toxicity


Molecular mechanism of action

Risk Assessment

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Absorption, distribution, metabolism, and associated sites of toxicity of molds

Molds have the potential to cause harmful side effects to humans. Before they can cause such side effects, they must first enter the human body and then be distributed to the appropriate site within the body. Once the molds reach their intended site, they go through a basic metabolic process. It should be noted that the metabolic processes that each mold experiences is typically the same. Molds colonize on an organic food source, consuming it. Within the human body, the byproduct of such process is typically a poison to humans, called mycotoxin.

Mycotoxins are the reason for the adverse health effects in humans. These health effects include inflammations, allergies, and/or infections. Mold spores enter the body through inhalation and ingestion. They can also be absorbed into the body through the skin. Once they enter the body, they can become harmful depending on the sensitivity of the individual, toxicity of the mold, and susceptibility of the exposed individual. It has been found that mold spores that are inhaled have greater toxicity to humans than those absorbed by the skin or ingested. Molds can also be an antigen to the body.

Molds tend to attack different systems of the human body depending on their form and how they enter the body, whether through ingestion, inhalation or absorption. In this section, the basic absorption/entrance, distribution to sites, and sites of toxicity are discussed.

Inhalation exposures

Mold contaminated ductwork.

Mold spores are probably most well known for their ability to cause sensitization and allergic responses. We are also exposed to their airborne byproducts. Either way, airborne exposure to mold remains the biggest concern when looking at molds and their affects on human health.

Sensitization and allergic reactions

There are several diseases that are correlated with the sensitization of the human body to a wide range of species of molds that are inhaled. This section only covers a few of the more common diseases caused by sensitization and in turn, allergic reactions to inhaled molds. First it is important to understand the basic pathology of sensitization and allergic reactions.

When exposed to high enough concentrations of specific molds, the body sees the intruding mold as a harmful foreign body and begins to attack it through the production of antibodies. These antibodies attack the intruding body called an antigen. The reactions of the antibodies attacking the antigens are considered allergic reactions.

Once the body becomes sensitized to what it is that it is exposed to, antibodies are formed. These antibodies are programmed into the body’s immune system to attack any repeat intruders, therefore each time an individual is exposed to a contaminant they are sensitized to, an allergic reaction can be expected. This is the same case with mold exposures when the molds are inhaled.

When molds are inhaled they are filtered out at various stages of the respiratory system. The point at which the molds begin to accumulate, or colonize, is considered the site of toxicity. The sites of toxicity are the exact locations within the body, which experience the physiologic side effects of the mycotoxins produced by the molds invading the area. Some molds cause sensitization in the upper respiratory system. Others pass through the respiratory system and enter the bloodstream, potentially sensitizing internal organs. Following are brief discussions on diseases caused by inhalation of molds.


Sinusitis is caused from sensitization from inhaling mold spores into the paranasal sinuses. There are four different pairs of sinuses that can be affected. These include the frontal (over the eyes), maxillary (inside the cheekbones), ethmoid (at the bridge of the nose between the eyes) and the sphenoid (behind the ethmoid). Each of these four causes a different sensitization. However, each of these sinuses branch into the nasal passage for exchange of air and mucous. During this exchange mold spores can be taken into one of the four different regions of the sinus.

A: Frontal sinus; B: Sphenoid sinus; C: Superior concha (turbinate);
D: Middle concha (turbinate); E: Inferior concha (turbinate); F: Auditory tube opening

Upon entering one of the sinuses, an allergic reaction takes place causing inflammation and closing of the sinuses to the nasal. Once this happens, pressure builds up within the sinus, causing a painful sensation to the individual. These infections can last from a couple of days to longer than a month. A specific type of sinusitis is allergic mycotic sinusitis where colonies of mold adhere to the sinus walls, causing inflammation.

Hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP), also called extrinsic allergy alveolitis (EAA), is a sensitization reaction to repeated inhalation of organic dusts. The organic dusts contain specific antigens, causing a variety of reactions. Sources of such organic dusts include grains, animal dander, and decaying vegetation. Over 300 sources of HP have been identified, not all of which are mold related. Each sensitization is coined with a different name such as bird fancier’s lung and farmer’s lung to name a couple. These are often named after the occupational exposure, but typically have the same health effects.

Chest radiograph of a patient with chronic hypersensitivity pneumonitis (HP) from pigeon breeder's disease. Bilateral reticulonodular densities are present.

Upon inhaling these dusts, they pass through the respiratory system. Those particles that reach the small airways and alveolar level are the particles of concern. When sensitized to a particular dust, the lower portion of the lungs releases enzymes and leukotrienes. The affects of these degrade the functionality of the lungs over time.

Allergic rhinitis

Also known as hay fever, allergic rhinitis develops after sensitization of individuals to airborne contaminants. Once sensitized, antibodies are formed to fight specific allergens. The antibodies also attach to mast cells located in the nose and eyes, which then releases histamines. These histamines cause itching of the eyes, sneezing, congestion and dripping of the nasal. Thus being exposed to certain airborne mold species, individuals can react within a short amount of time. One in five Americans are believed to have allergic rhinitis. Persistent allergic rhinitis may develop into sinusitis.

Bronchopulmonary mycosis

Inhaled mold spores may sometimes establish colonies within the bronchial passageways. Once they colonize mycotoxins are produced and bronchopulmonary mycosis is diagnosed. If left untreated, may develop into fibrosis of the lung.

Allergic asthma

Asthma is an inflammation or constriction of the lung airways. Reactions can take place that increase the severity of such inflammation and constriction. One such reaction is through allergic sensitization. In such cases, an individual inhales a mold in which they have developed sensitivity towards. Upon entering the airways, the mold triggers an asthmatic response where the airways become inflamed, making it difficult to breath.

Asthma in the upper respiratory system.

By-product reactions

Volatile Organic Compounds

In our everyday environment, fungi break down a wide range of organic material to produce byproducts of carbon dioxide, water, and chemicals called volatile organic compounds (VOCs). These chemicals are volatile because they evaporate at room temperature, thus mixing easily into the ambient air.

Stachybotrys chartarum growing on the backside of water damaged sheetrock behind a basement shower stall. A high water table caused flooding in the basement.

VOCs enter the body through the respiratory system via inhalation. Some compounds are absorbed by the upper respiratory system, causing irritation and inflammation through sensitization and allergic reactions. Other compounds, depending on the size and mass are able to reach the respirable levels of the lung, down into the alveoli where they may enter the blood stream. Upon entering the blood stream, VOCs can be carried to a variety of organs or systems depending on their chemical properties.

Since these chemicals are inhaled, they typically cause irritation to the mucous membranes of the upper respiratory system. However, they can also affect the central nervous system (CNS) if present in large enough concentrations and they are able to enter the blood stream. Affects on the CNS include headaches and a lack of concentration. VOCs also affect the trigeminal nerve, which is responsible for the body’s “fight or flight” response, by slowing down the necessary reactions.

Ingestion exposures

Ingestion of mold occurs primarily on accident. Accidental ingestion of mold can occur through hand-to-mouth activity or accidental ingestion of spoiled food. The majority of people do not attempt to eat spoiled food. If it is questionable whether the food is spoiled (moldy) or not, we inspect it using sight and smell. Food appearing to be spoiled is then thrown out.

Purdue researcher Tesfaye Mengiste has identified the gene responsible for causing a fuzzy, gray mold that attacks fruits, such as strawberries and tomatoes. (Purdue University photo by Tom Campbell).

Ingested molds can cause many of the diseases inhaled molds do if they can enter the bloodstream. The typical health effects occur in the digestive system (stomach and intestine). Molds can irritate the digestive system causing diarrhea, dehydration, nausea or stomach cramps. No specific diseases related to mold ingestion were identified.

Dermal absorption exposures

By far the least common route of exposure to mold, absorption of mold through the skin does occur. Humans commonly come into contact with molds in the natural environment. These molds are present on nearly every surface we come into contact with during a normal day. However, through personal hygiene, we are able to remove any mold contamination to ourselves before they become a health problem. When we do not or are unable to clean out skin surface regularly, some diseases could exist.


Renewal and Crisis Management - Mold Testing. 11/19/03

Mold: Volatile Organic Compounds and Mycotoxins: A Primer of Homeowners. 11/24/03

Mold, Toxic Molds and Indoor Air Quality. 11/19/03

National Institutes of Health, US Department of Health & Human Services - Sinusitis. 11/19/03

University of Oregon Health Center - Allergic Rhinitis (Hay Fever). 11/19/03

SD Mold Advanced Mold Inspections - Advanced Mold Inspections. 11/19/03

The Respiratory Institute - What is Asthma. 12/1/03

E Medicine – Hypersensitivity Pneumonitis. 11/24/03

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