Science Inventory

Understanding the impact of molds on indoor air quality and possible links to health effects Indoor Molds - More than Just a Musty Smell


WARD, M. D. Understanding the impact of molds on indoor air quality and possible links to health effects Indoor Molds - More than Just a Musty Smell. Presented at Veterinary Comparative Respiratory Society Meeting, Raleigh, NC, September 27 - 28, 2010.


This abstract is an invited talk to the Veterinary Comparative Respiratory Society's symposium 9/27-28-/2010. The talk presents an overview of indoor ai mold exposures and the impact on health effects


Molds are multi-celled, colony forming, eukaryotic microorganisms lacking chlorophyll belonging to the Kingdom Fungi. Furthermore, molds are ubiquitous in both indoor and outdoor environments. There are more than 200 different types of fungi to which people are routinely exposed (NAS. 2000). The growth of molds in homes, schools, offices, and other public buildings has been implicated as the cause of a wide variety of adverse health effects. Headlines resulting from moldy, water-damaged homes, particularly "toxic molds" and the aftermath of hurricanes on the east and gulf coasts have raised public awareness and concern regarding molds as potential health hazards, particularly in indoor environments. Molds are important indoor contaminants that require warm, humid places and a nutrient source. The nutrient source can be virtually anything organic including building materials such as drywall paper and wood as well as components in settled dust and food stuffs. Although water is critical for mold growth low levels may be sufficient. In general terms, different species of molds have different effects ranging from beneficial to harmful. Benefit is derived from molds that play an important role in the decay of organic matter (recycling at its best). Additionally, molds are a source of antibiotics, e.g. penicillin, food stuffs, and crop pest control. However, from a human prospective some molds cause harm. Examples would include plant pathogens which cause crop damage potentially leading to increased food costs or crop shortages as well as those molds that induce adverse health effects. Generally, more than one species is growing in a given environment. The presence of multiple species makes the determination of cause-effect relationships more difficult. Additionally, the possibility of cross-species interactions further complicates distinguishing the harmful from the benign. Respiratory exposures to fungi have been associated with an array of adverse health effects including frank infection, neurotoxicity (mycotoxin), respiratory tract conditions ranging from irritation to hypersensitivity responses such as allergy and asthma, and pulmonary hemosiderosis. Although there are fungi that infect the skin, hair, and nails, in general, serious systemic infections are caused by opportunistic organisms. In most cases these infections occur in people with a comprised immune system such as those undergoing chemotherapy or those with AIDS. The lung is often the target organ making inhalation the primary route of exposure. However, these infections are considered rare compared to bacterial infections. Another source of possible adverse health effects is exposure to low molecular weight. secondary metabolites called mycotoxins. Mycotoxins are toxic byproducts of some but not all molds and are not produced under all growing conditions. Mycotoxin exposure can be by skin contact, ingestion, or inhalation and have been found to have effects ranging from immuno-modulating to carcinogenic effects. Although ingestion has generally considered the primary route for both acute and chronic mycotoxin poisoning, mycotoxins have also been associated with health effects resulting from inhalation exposures. However, adverse health effects resulting from mycotoxin inhalation exposure are still controversial. This is in part due to unreliable assessment metrics (exposure dose levels, production in building materials), but limited availability of good scientific evidence is also an important factor. Immune hypersensitivity responses can be induced by mold exposures. Certain occupational exposures to fungi have been associated with hypersensitivity pneumonitis (e.g. Aspergillus species with tobacco worker's lung, Penicillium caseiwith cheese washer's lung, and P. chrysogenum with woodworker's lung) and allergy/asthma (e.g. Saccharomyces cerevisiae with baker's asthma). IgE-mediated allergic diseases occur in a genetically predisposed population in response to foreign substances (proteins) that should be innocuous. Allergic diseases and include: asthma, allergic rhinitis, conjunctivitis, and allergic sinusitis. Asthma prevalence has increased over the last several decades for reasons that are thought to have an environmental component. It is estimated that up to 90% of asthmatics are atopic and have an allergy trigger for asthmatic episodes. Additionally, it has been estimated that up to 10% of people have fungal allergies. Although human studies have shown associations with molds and allergy and asthma, animal studies have demonstrated a cause-effect relationship for allergy sensitization and asthma-like responses. Additionally, in dose-response animal studies comparing responses from exposures to mold extract and house dust mite (a well characterized indoor allergen) the molds demonstrated differential capacities (potencies) to induce allergic/asthma-like responses. These studies also suggest that there are threshold doses for allergy induction. Not all molds were able to cause allergic responses in the animal model but some of these molds may have components that exacerbate asthmatic responses. These studies suggest a role for molds in allergic asthma. Summary: Molds are ubiquitous in both indoor and outdoor environments. Their role in adverse health effects is not always clear. Systemic infection is considered more limited in the general population but the lung, thus inhalation exposure, is often the target organ. The role of mycotoxin inhalation in adverse health effects is still controversial. However, it is clear that these agents have the potential to cause effects from immunosuppression to cancer to neurotoxic effects. Animal studies indicate that there is a cause-effect relationship for molds in the induction of allergy and asthma-like responses in a mouse model. These effects require multiple pulmonary exposures and occur in a dose-response manner suggesting exposure thresholds for immune responses. Various molds have differing capacities to induce allergic asthma-like responses, i.e. not molds cause allergic responses

Record Details:

Product Published Date: 09/28/2010
Record Last Revised: 09/26/2016
OMB Category: Other
Record ID: 230283