Health Risks of Dampness or Mold in Workplaces and Schools

High School; three highrise buildings

Relative to research on the health risks of dampness and mold in houses, much less research has been performed on the health risks of dampness and mold in workplaces and schools. However, the available evidence suggests that the health risks in these buildings may be substantial. One of the downloadable papers available from this web site [15] includes tables that compile the characteristics and key findings of research on the relationship between dampness or mold and occupant respiratory health in offices and institutional buildings and schools. Eight studies of offices and institutional buildings and fourteen studies of schools were reviewed in this paper. One more recent study of dampness in offices [53], three studies in schools [54-56], one study in a variety of workplace types [57], and one study in daycare buildings [58] have since been identified. The studies measured a variety of dampness-related risk factors and employed a variety of study designs. Investigated risk factors in offices and institutional buildings included microbial agent concentrations in the air or in chair or floor dust [59-61], dampness in the building at large [62-64]; or poor cooling coil drain pan drainage in the air conditioning system [65]. One study was an intervention study using ultraviolet germicidal irradiation of wetted cooling coils in the air conditioning system to prevent microbial growth on the coils [66]. For schools, the major investigated risk factor for six studies (described in seven papers) was microbial agent concentrations in the air or in dust on floors; or visible/odorous signs of mold or dampness [54, 56, 67-72]. The major risk factor for the remaining nine studies (described in ten papers) was dampness or mold in buildings at large [73-82]. For both categories of buildings, most studies included design features and analysis methods designed to quantify the health risks of the dampness-related risk factors while controlling for the possible effects of other factors that affect the same health outcomes.


Based on this review, the evidence supporting an association of dampness or mold in office buildings with respiratory or other health effects of occupants is reasonably robust. Every study identified found at least one statistically significant association between dampness or mold and adverse respiratory or other health effects. In many of the studies, the increased risk of health effects in damp or moldy buildings was appreciable. For example, in a study performed within 21 offices from four buildings, the odds ratio for respiratory symptoms was 1.87, indicating moderately less than an 87% increase in symptoms where mold levels in chair dust were elevated [59]. Another study performed in a twenty-story water-damaged office building, reported an odds ratio of 1.7 for lower respiratory symptoms, indicating moderately less than a 70% increase in symptoms, when comparing subjects with the highest versus lowest concentrations of mold in floor dust [60]. In both cases the increases in symptoms were statistically significant. Another study investigated whether dampness in offices was associated with sick leave due to respiratory health symptoms [53]. Workers from offices with dampness had a 30% increase in sick leave, and the increase was statically significant. In many of the studies, the risk of at least one health effect increased more than 100%, indicating more than a doubling of risk. There were no statistically significant inverse findings of improved health with dampness or mold. The health outcomes found to increase with dampness and mold, (e.g. lower respiratory symptoms typical of asthma, mucous membrane symptoms, headache, and fatigue) are the same as those found to be associated with dampness and mold in housing.

One of the strongest studies from offices was an intervention study [66] that used ultraviolet germicidal irradiation of the wetted sections of air conditioning systems of three office buildings located in Montreal, which has a humid summertime climate, to reduce mold and bacteria growth on the wetted surfaces. The germicidal irradiation was turned off for twelve weeks and then on for four weeks, over a 48 week study. Seven hundred and seventy one occupants of the buildings, who were not informed when the irradiation was on or off, reported various health symptoms on questionnaires. There were statistically significant reductions in mucosal and respiratory symptoms, by approximately 30% and 40%, respectively, when the irradiation was on compared to when it was off. There were dramatic 99% reductions of microorganisms on the wetted surfaces of the air conditioning systems when the irradiation was on compared to off but no clear reductions in airborne mold spores or bacteria at work sites.

The results of two cross-sectional studies also suggest that microbial growth in air conditioning systems can increase risks of health symptoms. In a survey of 80 complaint office buildings from the U.S. [65], there was more than a 100% increase in the number of subjects with combinations of wheeze, shortness of breath, tight chest and cough in buildings with poor drainage of condensate from the cooling coil drain pan — which is presumed to increase the risks of microbial growth. In a survey of 100 non-complaint U.S. office buildings, humidification systems with a poor condition or poor maintenance and less frequent cleaning of cooling coils and condensate drain pans were associated with approximately 50% to 70% increases in various building related symptoms [83]. The findings from both of these studies were statistically significant.

Clockwise: Mold growing on a heater; floor dust; a young boy and girl sitting in front of a computer; mold spores.


Many of the studies from schools also showed significant health risks from dampness and mold, but the overall evidence of increased health risks from dampness in schools is not as consistent and robust as the evidence of increased health risks in damp offices. In particular, many studies included a small number of schools — sometimes only one damp and one dry school, so there is a substantial chance that building factors other than dampness and mold that differed among the damp and dry schools could have caused the reported differences in health outcomes. A second major weakness is that many studies had a small number of subjects leading to poor statistical power for detecting increased health risks among occupants of damp and moldy schools. Several studies are described below:

  • In the largest study, of 2751 schools within New York [56], students' absence rates were generally higher in schools with indications of moisture or mold problems, and, for about half of the indicators of moisture and mold, the increases in absence were statistically significant. The analyses of study data did control for several potential confounding factors such as measures of socio-economic status and pupil-teacher ratio. The study design has some inherent weaknesses including use of pooled data for the whole school, as opposed to data for individual students.
  • Another large study, involving 4365 students in 24 damp schools and eight dry schools, reported statistically significant 40% to 50% increases in some categories of cough symptoms in the damp schools, but no significant increases in other health symptoms [75].
  • A study of 1077 students from eight schools in Japan [54] found a statistically significant increase in nasal symptoms in classrooms with increased dampness, after control for several potential confounding factors. For eye symptoms, cough, and skin symptoms, the associations with dampness were inconsistent and not statistically significant.
  • A study of just over 1000 students in eight damp and seven dry schools reported statistically significant and larger than 100% increases in throat irritation, headache, and dizziness where mold counts in floor dust were higher; however, symptoms did not increase if the schools had more visible "moisture and mold patches" [68]. Subsequent additional analyses of the data from this same study found that the increases in symptoms with higher levels of molds in floor dust occurred only in boys and not-yet-menstruating girls [69].
  • A study of 762 students from 28 classrooms in eleven schools reported statistically significant increases in current asthma in classrooms with higher mold and bacteria counts in air and with higher indoor air relative humidity [72].
  • A study of 654 students from 46 classrooms in Europe [55] found that classrooms with higher airborne levels of mold, determined via culture-plate methods, had statistically significant increases in dry cough at night, persistent cough, and rhinitis (nasal inflammation with secretion or congestion), after controlling for several potential confounding factors. Increases in some specific types of molds in dust, from DNA-based analyses, were also linked to wheeze, rhinitis, and cough, and with measures of lung function.

Other studies in schools tended to be smaller or to use weaker designs. Despite the study weaknesses mentioned above, the overall results indicate that adverse health outcomes are likely to be elevated among occupants of damp and moldy schools. Many of the studies found that damp or moldy schools, or molds and bacteria in floor dust were significant risk factors for a variety of health outcomes. Only one study [67] reported an inverse finding of improved health (building related symptoms) with dampness or mold and this same study also reported significant worsening of throat, headache, and dizziness symptoms with increased mold in floor dust. Taken in isolation, the schools literature could be interpreted as non-conclusive. However, the consistency of findings from these school-based studies with the findings from homes and offices strengthens the case for adverse health effects in damp and moldy schools.

Other Building Types

Three studies of dampness or mold in other types of workplaces or in multiple types of buildings were identified. One of these studies assessed the associations of respiratory and other health symptoms in daycare workers with workplace mold, flooding, and water damage, or with "dampness", defined as any of these three parameters [58]. The analysis controlled for the effects of age, gender, and education. Nasal symptoms, cough, and wheeze were increased among workers in damp daycare buildings, with odds ratios of 1.8 to 2.9, and the increases were statistically significant. Bronchitis and allergic rhinitis were also elevated among the workers in damp daycare centers, but the increases were not statistically significant. The second study assessed associations between indoor dampness and respiratory symptoms in daycare centers, office buildings and domestic environments [61] and found that shortness of breath was increased in buildings with mold, and the increase was statistically significant. The third study included a variety of types of workplaces, primarily offices, schools, and health care buildings. Karvala et al. [57] investigated whether working for an extended period in a building with dampness was linked to the development of asthma. They found that workers that initially had asthma-like symptoms, but no diagnosed asthma, were more likely to subsequently develop diagnosed asthma if they worked in a damp space that was not remediated.

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