Mold And Your Health

Indoor Mold Contamination is a Threat to Health

The Fungus Among Us

Molds, a subset of the fungi, are ubiquitous on our planet. Fungi are found in every ecological niche and are necessary to recycle organic building blocks that allow plants and animals to live. Included in the group “fungi” are yeasts, molds, and mildews, as well as large mushrooms, puffballs, and bracket fungi that grow on dead trees. Fungi need external organic food sources and water to be able to grow. Continue reading to learn more about mold treatment.


Molds have varying requirements for moisture, food, temperature, and other environmental conditions for growth. Molds can grow on cloth, carpets, leather, wood, sheetrock, insulation (and on human foods) when moist conditions exist (Gravesen et al., 1999). Because molds grow in moist or wet indoor environments, people can become exposed to molds and their products, either by direct contact on surfaces or through the air, if mold spores, fragments, or mold products are aerosolized. Many molds reproduce by making spores, which, if they land on a moist food source, can germinate and begin producing a branching network of cells called hyphae.

Molds can have an impact on human health, depending on the nature of the species involved, the metabolic products being produced by these species, the amount and duration of individual’s exposure to mold parts or products, and the specific susceptibility of those exposed. Health effects generally fall into four categories. These four categories are allergy, infection, irritation (mucous membrane and sensory), and toxicity.


The most common response to mold exposure may be an allergy. Atopic people, that is, who are genetically capable of producing an allergic response, may develop symptoms of allergy when their respiratory system or skin is exposed to mold or mold products to which they have become sensitized. Sensitization can occur in atopic individuals with sufficient exposure.

While thousands of different molds can contaminate indoor air, purified allergens have been recovered from only a few of them. This means that atopic individuals may be exposed to molds found indoors and develop sensitization, yet not be identified as having mold allergies.


Infection from molds that grow in indoor environments is not common, except in certain susceptible populations, such as those with immune compromise from disease or drug treatment. A number of Aspergillus species that can grow indoors are known to be pathogens.

Mucous Membrane and Trigeminal Nerve Irritation

The third group of possible health effects from fungal exposure derives from the volatile compounds (VOC) produced through fungal primary or secondary metabolism and released into indoor air. Some of these volatile compounds are produced continually as the fungus consumes its energy source during primary metabolic processes. They produce alcohols or aldehydes and acidic molecules. Such compounds in low but sufficient aggregate concentration can irritate the mucous membranes of the eyes and respiratory system. Just as occurs with human food consumption, the nature of the food source on which a fungus grows may result in particularly pungent or unpleasant primary metabolic products. Certain fungi can release highly toxic gases from the substrate on which they grow.

Fungal volatile secondary metabolites also impart flavors and odors to food. Some people consider these compounds to have a pleasant or “clean” odor, depending on the concentration. As in certain cheeses, some of these are deemed desirable, while others may be associated with food spoilage. At higher exposure levels, VOCs from any source are mucous membrane irritants and can have an effect on the central nervous system, producing such symptoms as headache, attention deficit, inability to concentrate, or dizziness.

Adverse Reactions to Odor

Odors produced by molds may also adversely affect some individuals. The ability to perceive odors and respond to them is highly variable among people. Some individuals can detect extremely low concentrations of volatile compounds, while others require high levels for perception. An analogy to music may give perspective to odor response. What is beautiful music to one individual is unbearable noise to another.


Molds can produce other secondary metabolites such as antibiotics and mycotoxins. Antibiotics are isolated from mold (and some bacterial) cultures, and some of their bacteriotoxic or bacteriostatic properties are exploited medicinally to combat infections.

Mycotoxins are also products of the secondary metabolism of molds. And vary in specificity and potency for their target cells. Not all molds produce mycotoxins, but numerous species do (including many found indoors in contaminated buildings). Toxigenic molds vary in their mycotoxin production depending on the substrate on which they grow. Until relatively recently, mold poisons were regarded with concern primarily as contaminants in foods.

Because indoor samples are usually comprised of a mixture of molds and their spores, it has been suggested that a general test for cytotoxicity be applied to a total indoor sample to assess the potential for hazard as a rough assessment.

The following summary of toxins and their targets is adapted from Smith and Moss (1985), including a few more recent literature additions.

Vascular system (increased vascular fragility, hemorrhage into body tissues, or from lung, e.g., aflatoxin, satratoxin, roridins).
Digestive system (diarrhea, vomiting, intestinal hemorrhage, liver effects, i.e., necrosis, fibrosis: aflatoxin; caustic effects on mucous membranes: T-2 toxin; anorexia: vomitoxin.
Respiratory system: respiratory distress, bleeding from lungs, e.g., trichothecenes.
The nervous system, tremors, incoordination, depression, headache, e.g., tremorgens, trichothecenes.
Cutaneous system: rash, burning sensation sloughing of skin, photosensitization, e.g., trichothecenes.
Urinary system, nephrotoxicity, e.g., ochratoxin, citrinin.
Reproductive system; infertility, changes in reproductive cycles, e.g., T-2 toxin, zearalenone.
Immune system: changes or suppression: many mycotoxins.

It should be noted that not all mold genera have been tested for toxins, nor have all species within a genus necessarily been tested!


Penicillium species have been shown to be fairly common indoors, even in clean environments, but certainly begin to show up in problem buildings in numbers greater than outdoors (Burge, 1986; Miller et al., 1988; Flannigan and Miller, 1994). Spores have the highest concentrations of mycotoxins, although the vegetative portion of the mold, the mycelium, can also contain the poison. The viability of spores is not essential to toxicity so that the spore as a dead particle can still be a source of the toxin.

Important toxins produced by penicillia include nephrotoxic citrinin, produced by P. citrinum, P. expansum and P. viridicatum; nephrotoxic ochratoxin, from P. cyclopium and P. viridicatum, and patulin, cytotoxic and carcinogenic in rats, from P. expansum (Smith and Moss, 1985).


Aspergillus species are also fairly prevalent in problem buildings. This genus contains several toxigenic species, among which the most important are A. parasiticus, A. flavus, and A. fumigatus. Aflatoxins produced by the first two species are among the most extensively studied mycotoxins. They are among the most toxic substances known, being acutely toxic to the liver, brain, kidneys, and heart, and with chronic exposure, potent carcinogens of the liver. They are also teratogenic.

Symptoms of acute aflatoxicosis are fever, vomiting, coma, and convulsions (Smith and Moss, 1985). A. flavus is found indoors in tropical and subtropical regions and occasionally in specific environments such as flowerpots. A. fumigatus has been found in many indoor samples. A more common Aspergillus species found in wet buildings is A. versicolor, which grows on the wallpaper, wooden floors, fibreboard, and other building material. This mold is more often associated with the infectious disease aspergillosis, but this species does produce poisons for which only crude toxicity tests have been done.

Stachybotrys chartarum (atra)

Stachybotrys chartarum (atra) has been much discussed in the popular press and has been the subject of a number of building-related illness investigations. It is a mold that is not readily measured from air samples because its spores, when wet, are sticky and not easily aerosolized. This organism has a high moisture requirement, so it grows vigorously where moisture has accumulated from roof or wall leaks or chronically wet areas from plumbing leaks. It is often hidden within the building envelope.

S. chartarum has a well-known history in Russia and the Ukraine, where it has killed thousands of horses, which seem to be especially susceptible to its toxins. These toxins are macrocyclic trichothecenes.

While there are insufficient studies to establish cause and effect relationships between Stachybotrys exposure indoors and illness, including acute pulmonary bleeding in infants, toxic endpoints and potency for this mold are well described. What is less clear, and has been difficult to establish, is whether exposures indoors are of sufficient magnitude to elicit illness resulting from toxic exposure.

Conclusions and Recommendations

Prudent public health practice then indicates removal from exposure through clean-up or remediation and public education about the potential for harm. Not all species within these genera are toxigenic, but it is prudent to assume that when these molds are found in excess indoors, they are treated as though they are toxin-producing. It is not always cost-effective to measure toxicity, so cautious practice regards the potential for toxicity as serious, aside from other health effects associated with excessive exposure to molds and their products

Health effects from exposure to molds in indoor environments can result from allergy, infection, mucous membrane and sensory irritation, toxicity alone, or combination. Mold growth in buildings (in contrast to mold contamination from the outside) always occurs because of unaddressed moisture problems. When excess mold growth occurs, individuals' exposure, and moisture problem remediation must be addressed.


Harriet M. Ammann is a senior toxicologist for Washington State Department of Health, Office of Environmental Health Assessments. She provides support to a variety of environmental health programs, including ambient and indoor air programs. She has participated in evaluations of schools and public buildings with air quality problems and has presented on toxic effects from air contaminants, indoors and out, effect on sensitive populations, and other health issues throughout the state. Through her work, she has developed an interest in the toxicology of mold as an indoor air contaminant and has published and presented on mold toxicity relating to human health.