Health Risk of Dampness or Mold in Houses

Mold growing on the ceiling of a room; moisture damage in the corner of a basement.

Two recent comprehensive review articles, by the World Health Organization [4] in 2009 and by Mendell et al. in 2011 [40], have summarized current knowledge on health effects of damp and moldy buildings, based on the overall scientific literature. The WHO review was by a multidisciplinary group of experts, and the Mendell et al. review updated the WHO review. While including reviews of the literature on dampness and mold in buildings in general, most available findings pertained to homes. The conclusions paralleled and expanded those of the prior most comprehensive review, that by the Institute of Medicine (IOM) of the National Academy of Sciences [1]. The conclusions that include the most recent literature [40], from Mendell et al. (2011), were as follows:

  • Evident dampness or mold in buildings (such as visible dampness, visible water damage, visible mold, or mold odor), were consistently associated with increases in a number of diseases: development of new asthma, exacerbation of existing asthma, ever-diagnosis of asthma, current asthma, respiratory infections, bronchitis, allergic rhinitis (inflammation of nasal passages with runny nose or congestion), and eczema. They were also associated with increases in a variety of respiratory symptoms: difficulty breathing (dyspnea), wheeze, cough, and upper respiratory symptoms. Evidence was not strong enough to establish a direct causal link between dampness or mold in homes and any of these health outcomes (diseases or respiratory symptoms); however, evidence for a link between dampness and mold in homes and exacerbation of existing asthma in children was sufficient to strongly suggest a causal link.
  • There is also sufficient evidence associating hypersensitivity pneumonitis with dampness and mold in buildings. Hypersensitivity pneumonitis is a rare inflammatory lung disease with symptoms of cough, difficulty breathing, and fever, most often seen in work settings with very high exposures to biologic materials, and not generally seen with home exposures (with the exception of homes in Japan).
  • Only limited or suggestive evidence was available on whether building dampness or mold were associated with common cold and allergy; insufficient evidence was available to determine whether an association existed with altered lung function.

The review of Mendell et al. [40] focused on respiratory and allergic effects. A prior analysis by the Institute of Medicine [1] concluded at that time there was inadequate or insufficient evidence to conclude whether building dampness or mold were associated with other health effects including cancer, reproductive effects, rheumatologic or other immune diseases, chronic obstructive pulmonary disease, pulmonary hemorrhage (i.e., bleeding in lungs) in infants, skin symptoms, and fatigue. Note that concluding that evidence is inadequate or insufficient should not be equated with a conclusion that dampness and mold does not contribute to these health outcomes.

Based on these critical reviews, levels of culturable mold spores in the air or dust, visibly counted mold spores in air or dust, or various products or components of molds, were not consistently associated with health outcomes. Some were associated with both increases in some health effects and decreases in others.

Based on the available evidence, preventing and mitigating indoor dampness and mold are likely to reduce health risks in homes, but measuring levels of airborne fungal spores or concentrations or other microbial agents has no current scientific basis for use in guiding health-protective actions in homes.

Dampness itself, i.e., high moisture levels in portions of a building, is not considered to directly cause health effects. It seems likely that mold or bacteria growth in damp materials is involved in causing the above health effects, but the available evidence was insufficient to rule out a role for other pollutant exposures that are increased in damp and moldy buildings, such as chemical emissions from damp materials.

The above-mentioned three reviews have considered all subjective assessments of dampness and mold in homes together, and have not separately examined links of health effects to specific types of evident dampness or mold, such as visible mold, visible water damage, or mold odor. Most of the studies included in the reviews have been cross-sectional with the subjects or parents of subjects reporting the presence of dampness and mold. A recent study [41] followed a birth cohort and employed trained engineers to inspect homes for dampness and mold. This study found that increases in doctor-diagnosed and parent-reported wheeze were associated with dampness and mold in main living areas of the house, but not all associations were statistically significant. Respiratory infections were not consistently associated with dampness or mold.

A young boy using an inhaler.

Three additional focused analyses have been completed for this Scientific Findings Resource Bank. One, a quantitative statistical evaluation of the available scientific literature, produced estimates and uncertainty bounds for the average magnitudes of increases in various respiratory health effects in homes with dampness and mold [42]. The key results of this analysis are shown in Figure 1. For these analyses "current asthma" was defined as doctor-diagnosed asthma plus recent asthma symptoms, "ever diagnosed (dx) asthma" was defined as ever having been diagnosed with asthma, and "asthma development" was defined as development of the disease of asthma subsequent to the exposure to dampness or mold. The "odds ratio" was used as the primary measure of the increased risk of health effects in damp or moldy homes. The odds ratio is the odds of having the health effect if one resides in a home with dampness or mold divided by the odds of having the health effect if one resides in a home without dampness and mold. An odds ratio of unity would indicate no increased risk of having the health effect, an odds ratio of 1.5 would indicate that the increase in risk is moderately less than 50% (e.g., 37% to 44%) and an odds ratio of 2.0 would indicate that the increase in risk is moderately less than 100% (e.g., 75% to 88%). In the figure, the blue diamonds indicate the central or best estimate of the average odds ratio for the health outcomes and the vertical bars indicate the 95% confidence intervals for this estimate. If the 95% confidence interval does not extend below an odds ratio of unity (i.e., does not cross the green line), statistically we can be 95% confident that the prevalence of the health effect is increased in damp or moldy homes. The central estimates for odds ratios ranged from 1.4 to 1.7 and for five of six health outcomes the confidence interval excluded unity indicating a high statistical confidence that the risk of having the health effect is elevated in damp or moldy homes. To communicate the increases in risk in more familiar terms, the authors used the odds ratios to estimate the percentage increases in the health effects in damp or moldy homes and these estimates are shown by the red squares. In summary, building dampness and mold were determined to be associated with 30% to 50% increases in a variety of respiratory and asthma-related health outcomes and, for all health effects except development of the disease of asthma, the observed increases in these adverse health effects in damp or moldy homes were very unlikely to be the result of chance.

Figure 1. Results of analyses to quantify the average increases in health effects for occupants residing in homes with dampness or mold. [42]

Recently, similar statistical analysis methods were again employed [43] to quantitatively evaluate the published data on the relationship of dampness with health, incorporating the results available in more recently published journal papers. The findings are similar to those portrayed in Figure 1, but with slightly larger increases in health risks in homes with mold. Visible mold in homes was associated with increases in doctor-diagnosed asthma, wheeze and allergic rhinitis with odds ratios of 1.48, 1.68, and 1.39, respectively. In each case, the association was statistically significant. Another recent statistical analyses of the pooled data from 12 studies [44] also yielded similar findings. Mold exposure was associated with statistically significant increases in wheeze, asthma, bronchitis, nocturnal cough, morning cough, hay fever, and sensitization to inhaled allergens, with odds ratios of 1.3 to 1.5. These more recent results strongly support the results of the meta-analyses depicted in Figure 1.

A second analysis completed for this Scientific Findings Resource Bank estimated the U.S.-wide public health impact of dampness and mold in houses, focusing on current asthma, defined as doctor-diagnosed asthma plus recent asthma symptoms, as the health outcome [15]. The proportion of current U.S. asthma cases attributable to dampness and mold exposure was estimated to equal 21%, with uncertainty bounds of 12-29%. Of the 21.8 million people reported to have asthma in the U.S., approximately 4.6 (range: 2.7-6.3) million cases were estimated to be attributable to dampness and mold exposure in the home. The associated annual cost of current asthma attributable to dampness and mold in homes in the U.S. was estimated to be $3.5 billion (range: $2.1 - 4.8 billion).

A third analysis completed for the Scientific Findings Resource Bank was another quantitative statistical evaluation of the available scientific literature to estimate the magnitude of increases in respiratory infections and bronchitis in homes with dampness and mold [45]. As in the first analysis discussed above, the odds ratio was used as the primary measure of the increased risk of health effects in damp or moldy homes. For these analyses, the general category of "respiratory infections group" was defined to include viral or bacterial infections of the upper and lower respiratory tract, pneumonia, sinus or ear infections, tonsillitis, common cold, and acute bronchitis. The "specific respiratory infections" category started with the respiratory infections group and excluded common cold and non-specific respiratory infections that are sometimes difficult to distinguish from allergy symptoms. A number of separate analyses were performed for different groups of health effects. Dampness and mold were associated with increased risk of a number of specific types of health effects. As illustrated in Figure 2, odds ratios (and 95% confidence intervals) were: for acute or chronic bronchitis, 1.45 (1.34-1.56); for respiratory infections, 1.44 (1.32-1.58); for specific respiratory infections, excluding nonspecific upper respiratory infections that might actually be allergies, 1.42 (1.26-1.60); and for respiratory infections in infants or children with age less than 17, 1.48 (1.34-1.62). The analyses further estimated that from 8% to 20% of these health effects were potentially attributable to dampness and mold in houses, and might be preventable if these conditions were avoided.

dampness-fig2

Figure 2. Results of analyses to quantify the average increases in respiratory infections and bronchitis for occupants residing in homes with dampness or mold. [45]

A number of recent studies not included in the most current review papers have added to our understanding of the health effects of dampness and mold, although a finding from a single study should always be considered preliminary until sufficiently replicated by other studies. Hwang et al. [46] found strong relationships between development of new asthma in children and each of three types of evidence of dampness or mold in homes: mold odor, visible mold, and water damage. The risk of asthma associated with any of these exposures was also greater in children with an allergic parent. Jaakkola et al. [47] reported that past water damage, visible moisture, visible mold, and mold odor in homes was associated with the development over time of new allergic rhinitis (allergic inflammation of nasal passages with runny nose or congestion) in children. Norback et al. [48] found that dampness at home was associated over time with a decline in lung function among adult women. Reponen et al. [49] found that a summary index of fungi, identified by DNA-based methods, in home floor dust when children were one year old was strongly associated with the risk of developing asthma by age 7.

Despite the strong evidence of increased health risks in damp or moldy houses, only one sizable (i.e., involving many buildings) investigation of the health benefits of dampness-related remediations of houses was identified [50] (excluding the subsequently-described studies of health changes after remediations that focused on house dust mites). In this investigation, performed in Cleveland, the homes of 29 children with asthma received asthma control education, an extensive remediation (average cost $3458) that reduced moisture sources and removed and replaced water-damaged and moldy materials, and moisture-related modifications of heating, ventilating, and air conditioning (HVAC) systems. Families of 33 control children with asthma received only asthma control education. In moisture-remediated homes, mold scores based on standardized inspections decreased by 50 to 75% while in homes of control children the average decrease in mold score was 10 to 45%. Post-remediation mold scores were statistically-significantly lower in the remediated homes compared to control homes. Airborne counts of indoor-origin molds decreased by approximately 50% in the remediated houses but only by approximately 15% in the houses of control subjects. There were statistically-significant or nearly significant reductions of moderate size (e.g., 33%) in asthma symptom days among subjects in remediated homes but no statistically significant reductions among control subjects. Emergency room visits dropped markedly in the subjects from remediated homes but not in control subjects. The results of this remediation study provide support for the very substantial previously-described statistical evidence that home dampness and mold increase the risks of respiratory health effects.

Two review articles have conducted rigorous evaluations of the evidence for health benefits of mitigating dampness and mold in homes. One review concluded that combining the elimination of moisture intrusion and leaks with removal of moldy items was effective in reducing allergy and respiratory symptoms and was ready for broad use [51]. The other review concluded that there was moderate evidence that remediating dampness and mold problems in houses would decrease asthma-related symptoms and respiratory infections in adults, and visits for acute medical care in children [52].

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