All fungal species have the potential to cause health effects. Molds produce allergens, irritants, and in some cases, mycotoxins that may cause reactions in humans. The types and severity of symptoms depend, in part, on the types of mold present, the extent of an individual’s exposure, the ages of the individuals, and their existing sensitivities or allergies. Specific reactions to mold growth can include allergic reactions, asthma, hypersensitivity pneumonitis (i.e., resembles bacterial pneumonia and is uncommon), irritant effects, and opportunistic infections. People with weakened immune systems may be more vulnerable to infections by molds. Total airborne mold spores may include both viable (living) and nonviable (dead) microorganisms as well as loose pieces of microorganisms, and both viable and nonviable microorganisms have the potential of causing health effects.
Inhalation is the primary way that people are exposed to mold. Mold spores and fragments can become airborne and get into the air we breathe. People may also be exposed to mold through the skin (National Toxicology Program, 2013). The health effects from mold depend on the characteristics, magnitude, and duration of exposure. People who have an existing respiratory condition, such as asthma or allergies, are more likely to suffer adverse effects (National Toxicology Program, 2013).
It is well established that allergic reactions to molds are the most commonly experienced health effects in humans. Symptoms can range from sneezing to wheezing. Individuals without allergies may also experience symptoms, including eye irritation, sore throat, congestion, skin rash, and headaches (National Toxicology Program, 2013).
The National Academy of Sciences (2004) conducted a comprehensive literature review and analysis and found there was sufficient evidence to link mold and other factors related to damp indoor environments with some upper respiratory tract symptoms, coughing, wheezing, and asthma in sensitized persons or people who already have respiratory problems, the elderly, or the very young. However, NAS found there was not enough evidence to make conclusions for many other health outcomes, including rheumatologic and other inflammatory diseases, neurological symptoms, cancer, and reproductive effects (Institute of Medicine of the National Academies, 2004).
In research conducted in human populations, the World Health Organization (WHO) found sufficient evidence to show that occupants of damp and moldy buildings are at increased risk of respiratory symptoms, respiratory infections, shortness of breath, and worsening of asthma (WHO, 2009). In people who have a weak immune system, some molds may cause infections (National Toxicology Program, 2013).
There is a wide variability in how people are affected by airborne mold spore exposure. Currently, there is no established airborne concentration that is known to adversely affect any individual’s health. People may be affected more severely and quickly than others, including:
• Infants and children
• Elderly people
• Pregnant women
• Individuals with respiratory conditions or allergies and asthma
• Persons with weakened immune systems
A small group of molds are pathogens, which are capable of causing infections in both healthy people and those who suffer from immune suppression (National Toxicology Program, 2013). Molds that can produce mycotoxins under the appropriate environmental and competitive conditions can and do grow indoors. Damp indoor spaces may also facilitate the growth of bacteria that can have toxic and inflammatory effects (NAS, 2004).
Some fungi produce toxic metabolites (mycotoxins), and almost all molds that grow in the built environment can produce triple helical glucan, both of which are toxic to lung cells. Many studies in appropriate laboratory animals have demonstrated that very low exposure to these compounds can result in inflammation.
The most frequently studied mycotoxins are produced by species of Aspergillus, Fusarium, Penicillium, Stachybotrys, and Myrothecium. The kinds and amounts of toxin a fungus produces depend on the fungal strain, the substrate it is metabolizing, and possibly, the presence or absence of other organisms. Mycotoxins associated with Stachybotrys chartarurm include Saratoxins, Verrucarins, Roridins, and Stachybocins. ACGIH (1999, 2024) indicates that possible health effects from such mycotoxins include inflammation, suppression of the immune system, dermatitis, hemotoxicity, and hemorrhaging (ACGIH, 1999; ACGIH, 2024).
The presence of many biological agents in the indoor environment is due to dampness and inadequate ventilation. Excess moisture on almost all indoor materials leads to the growth of microbes, such as mold, fungi, and bacteria, which subsequently emit spores, cells, fragments, and volatile organic compounds (VOCs) into indoor air. Moreover, dampness initiates chemical or biological degradation of materials, which also pollutes indoor air. Dampness has therefore been suggested to be a strong, consistent indicator of risk of asthma and respiratory symptoms (e.g., cough and wheeze) (WHO, 2009).
Health Canada (2007) concluded from its review of scientific literature pertaining to the health effects of indoor molds that exposure to indoor mold is associated with an increased prevalence of asthma-related symptoms such as chronic wheezing, irritation symptoms, and non-specific symptoms (Health Canada, 2007).
Health Canada (2007) considers that mold growth in residential buildings may pose a health hazard. Health risks depend on exposure and, for asthma symptoms, on allergic sensitization. However, the large number of mold species and strains growing in buildings and the large inter-individual variability in human response to mold exposure preclude the derivation of exposure limits. Health Canada (2007) recommends:
To control humidity and diligently repair any water damage in residences to prevent mold growth
To clean thoroughly any visible or concealed mold growing in residential buildings (Health Canada, 2007).
Well conducted epidemiology studies in several countries have consistently shown that exposures from building/house dampness and mold have been associated with increased risks for respiratory symptoms, asthma, hypersensitivity pneumonitis, rhinosinusitis, bronchitis, and respiratory infections (AIHA, 2013; AIHA, 2024; Mendell, Mirer, Cheung, Tong, & Douwes, 2011; Quansah, Jaakkola, Hugg, Heikkinen, & Jaakkola, 2012). In studies conducted in the non-industrial workplace, individuals with asthma or hypersensitivity pneumonitis were found to be at risk for progression to more severe disease if the relationship between illness and exposure to the damp building was not recognized and exposures continued (AIHA, 2013; AIHA, 2024; Park & Cox-Ganser, 2011).
Three high quality, systematic reviews of the available evidence concluded that the implementation of interventions that combine elimination of moisture intrusion and leaks and removal of moldy items help to reduce mold exposure and respiratory symptoms and new onset asthma (AIHA, 2013; AIHA, 2024; Mendell, Mirer, Cheung, Tong, & Douwes, 2011; Quansah, Jaakkola, Hugg, Heikkinen, & Jaakkola, 2012; Krieger, et al., 2010). This position has also been taken by the National Institute for Occupational Safety and Health (NIOSH, 2012) and many state governments, Health Canada (2007), and internationally by the World Health Organization (2009) (NIOSH, 2012; Health Canada, 2007; WHO, 2009).
The American Industrial Hygiene Association (AIHA, 2008) recommends that occupants be isolated from a moldy environment in the following conditions:
• The confirmed presence of facultative pathogens (fungi capable of inducing pulmonary infections in humans) such as Aspergillus fumigatus and Aspergillus flavus; and
• The presence of fungi, such as Stachybotrys chartarum, is known to result in occupational diseases in part due to their potent toxins.
Furthermore, since Stachybotrys chartarum requires water-saturated conditions and is often difficult to recover by sampling methods, “some contamination” might mean much more (Prezant, Weekes, & Miller, 2008).
References
ACGIH. (1999). Bioaerosols: Assessment and Control. Cincinnati: ACGIH.
ACGIH. (2024). Bioaerosols Assessment and Control. 2nd Edition. (C. Marcham, & J. Springston, Eds.) Cincinnati, OH: ACGIH.
AIHA. (2013, March 26). Position Statement on Mold and Dampness in the Built Environment.
AIHA. (2024, October 9). Mold and Dampness in the Built Environment. White Paper, Version 3.
Health Canada. (2007). Residential Indoor Air Quality Guidelines: Moulds.
Institute of Medicine of the National Academies. (2004). Damp Indoor Spaces and Health. Washington, D.C.: The National Academies Press.
Krieger, J., Jacobs, D., Ashley, P., Baeder, A., Chew, G., Dearborn, D., . . . Zeldin, D. (2010). Housing interventions and control of asthma-related indoor biologic agents: a review of the evidence. Journal of Public Health Management & Practice, 16, S11-S20.
Mendell, M., Mirer, A., Cheung, K., Tong, M., & Douwes, J. (2011). Respiratory and allergic health effects of dampness, mold, and dampness-related agents: a review of the epidemiologic evidence. Environmental Health Perspective, 119, 748-56.
National Toxicology Program. (2013, June). Mold.
NIOSH. (2012). Preventing Occupational Respiratory Disease from Exposures Caused by Dampness in Office Buildings, Schools, and Other Nonindustrial Buildings. NIOSH Publication #2013-102. Cincinnati, OH: NIOSH.
Park, J., & Cox-Ganser, J. (2011). Mold exposure and respiratory health in damp indoor environments. Front Bioscience (Elite Ed.), 757-771.
Prezant, B., Weekes, D., & Miller, J. D. (2008). Recognition, Evaluation, and Control of Indoor Mold. Fairfax, VA: AIHA.
Quansah, R., Jaakkola, M., Hugg, T., Heikkinen, S., & Jaakkola, J. (2012). Residential dampness and molds and the risk of developing asthma: a systematic review and meta-analysis. PLoS One, 7(11), e47526.
WHO. (2009). WHO Guidelines for Indoor Air Quality: Dampness and Mould.