Health effects associated with exposure to indoor damp spaces and mold

Molds and other fungi grow easily in damp indoor environments. People who spend time in such environments sometimes complain of respiratory effects, headaches, and other physical symptoms. In addition to visible or hidden mold, damp spaces likely harbor mold break-down products, dust mites, bacteria, and chemicals, gasses, and particulate matter released from the materials on which molds are growing. Given the difficulties in testing for all of these elements, hard evidence of precise cause-and-effect can be elusive.

In an extensive 2004 report, the Institute of Medicine (IOM) did not find enough evidence to identify health effects which were definitely caused by spending time in damp indoor spaces. However, the experts found that being in damp indoor spaces seemed related to respiratory illnesses: nose and throat symptoms, cough, wheeze, and asthma symptoms. They also found limited evidence that these environments can be associated with shortness of breath, the development of asthma in people who did not previously suffer from it, and lower respiratory symptoms (coughing, wheezing, chest tightness, and shortness of breath) in healthy children. Based on available research, IOM was not able to substantiate claims of numerous other symptoms such as skin irritations, fatigue, cancer, lung disease, or respiratory infections. There was enough evidence of health effects overall, though, that IOM identified damp indoor spaces as a public health problem that needs to be addressed.

Publications in 2007, 2010, and 2011 did not substantially change those findings.They reiterate that there is evidence to support an association between damp spaces, indoor mold, and respiratory illnesses. Therefore, whether the precise cause is mold or an accompanying indoor contaminant, spending time in places damp enough to support the growth of mold is a potential cause of ill health. Whether or not mold is actually seen, finding and fixing the sources of excess moisture are important for health and to keep the structure from being further damaged. Researchers note that, if dampness and mold could be confirmed as a cause of ill health, controlling these conditions would make a substantial contribution to public health.

However, some authors state definitively that mold exposure is capable of causing illness in humans. For example:

  • Bush and colleagues summarize three mechanisms: harmful immune responses, e.g. allergies or the uncommon occurrence of hypersensitivity pneumonitis; infections; and irritation from mold by-products.
  • Some authors discount the role of mold in irritant responses but add toxicity to the list of acknowledged responses to mold exposure.
  • Yet others include all four mechanisms as possible causes of adverse health effects.
  • Terr describes four known types of allergy caused by inhaling mold spores, including asthma and a type of sinusitis.

Fisk and colleagues reviewed thirty-three studies to assess the risk of health effects in individuals who spent time in damp, moldy environments. Subjects were adults and children. They found that upper respiratory tract symptoms, cough, wheeze, and asthma were more frequent in people who spent time in damp spaces.

In a review of studies of children from ten countries, aged six to twelve, Antova and colleagues found that mold in the household correlated with a variety of respiratory disorders, including wheezing, coughing at night, and allergic symptoms and hay fever.

Park and colleagues reported an increase in new-onset asthma among employees working in a water-damaged office building. There was a correlation between the onset of asthma and mold levels in the building’s dust.

Karvonen and colleagues studied a group of 396 children for the first eighteen months of life and found that wheezing was more common in children whose homes had moisture damage in the kitchen and visible mold in the primary living areas. Different findings were published by Dales and colleagues. They studied a group of 357 children for the first two years of life and found no correlation between respiratory illness and mold.

Allergies and Asthma

As suggested above, there are hundreds of studies reaching a variety of conclusions. It can be difficult or impossible to assess all types of molds, spores, fungal fragments, chemicals from destruction of mold-colonized materials and second-hand smoke, and other airborne matter indoors at any given time. Though numerous studies associate the presence of dampness and mold with respiratory allergies and asthma, it can be equally difficult or impossible to establish the presence of these substances as the definitive cause of illness in particular patients.

Even so, it is possible to assess and treat individuals who have symptoms of respiratory allergies and asthma. Khalili and colleagues emphasize that determining whether respiratory symptoms are related to mold exposure involves a process of elimination. Before mold is considered the likely cause of respiratory symptoms and infections, patients must be evaluated for the possible presence of pre-existing illness or the recent onset of an illness that happens to coincide with mold exposure. Once other possible causes of respiratory symptoms have been ruled out, patients can be assessed for the possibility of mold-induced illness.

In a lengthy document, Storey and colleagues identify three groups of patients to be assessed for mold exposure: those who present with symptoms often associated with wet spaces and mold; those whose symptoms occurred at the time of a presumed exposure to mold or damp spaces; and patients concerned about exposures to mold even though they have no symptoms.

In any case, a medical diagnosis is needed. For example, does the person have an allergy, asthma, or an infection? There are established methods for diagnosing these and many other conditions. Diagnosis is related to the disease process, not a specific trigger. For example, it is possible to test people for allergies to molds, but positive results do not necessarily correlate with symptoms. A sizeable percentage of the U.S. population will test positive for mold allergens but have no symptoms; estimates range from 3 percent to more than 90 percent. And generally speaking, treatments will not differ if the cause is mold exposure versus other triggering conditions.


Spending time in damp and moldy buildings seems to increase the risk of bronchitis and respiratory infections, but is not proven to do so. If it is a cause of these infections, bacteria or chemical emissions are likely to be responsible.

There are well-known fungal infections, but they are not typically a result of exposure to indoor molds. Examples include:

  • Allergic bronchopulmonary aspergillosis. Although Aspergillus is a fungus found indoors and outdoors, people who develop this condition usually suffer from asthma, cystic fibrosis, or immune deficiency. The illness is related to the anatomy of the lung, not exposure to indoor molds.
  • Athlete’s foot and thrush are among many fungal infections that are not related to the presence of indoor mold.

Pulmonary hemorrhage

In the 1990s, several children in Cleveland, OH, developed pulmonary hemorrhage (bleeding in the lungs). One of those children died. A preliminary study identified exposure to mold, particularly mycotoxins from Stachybotrys chartarum, as a possible cause of these illnesses. On further review, however, the U.S. Centers for Disease Control and Prevention (CDC) determined that the earlier analyses were in error and that the cause remained unknown. CDC also noted that a similar cluster of cases in Chicago was not associated with mold exposure and that pulmonary hemorrhage was not consistent with what is known of exposure to this fungus.

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