Concentrations of allergens in floor dust are commonly considered a proxy for allergen concentrations in air. Also, dust allergen concentrations are used as indicators of the risks of allergen-related health effects. Based on studies in homes, researchers have identified the concentrations of various types of allergens in floor dust that are considered sufficient to cause occupants to become allergically sensitized or, in some cases, to have allergic or asthma symptoms. The allergen concentrations in dust from homes that are associated with allergic sensitization have been used to interpret allergen data from schools. Such interpretations of school allergen data are imperfect because less time is spent at school than at home and because children are not at school during the first few years of life.
Several studies have measured concentrations of allergens in samples of floor dust from schools. Fewer studies have measured allergen concentrations in school air or in dust from surfaces of desks. From studies of schools, the concentrations of allergens from cats, dogs, cockroach, and mice have been most commonly measured. The concentrations of allergens measured in schools have varied considerably among studies probably because of variability in pet ownership by students' and teachers' families and because of variability among climates, school maintenance practices, school physical features, and school cleaning practices. Variability in allergen sampling and analysis methods are also factors. Pet ownership is important because students and teachers transport allergens attached to their clothes from homes to schools [1, 2]. Floor covering type has also been shown to be important. Based on a review, higher concentrations of cat, dog, and mite allergen are found in dust from carpeted, as opposed to hard surface, school floors . Cleaning methods and frequencies affect the levels of allergens that accumulate on indoor surfaces .
The main source of pet allergens in schools is thought to be transport of allergens on clothes from the homes of families with pets. Studies have found that concentrations of cat and dog allergen from school floor dust samples often exceed cat and dog allergen concentrations in floor dust of homes without pets [2-6]. A study in Norway  found average cat allergen concentrations on carpeted floors of schools that were approximately ten times average cat allergen on carpeted floors of homes without cats, although the variability in concentrations among homes and among schools was very large. However, dust from schools typically has a much lower pet allergen concentrations than dust from homes with pets. For example, in a home with cats, the concentrations of cat allergen concentrations will normally be much higher than in schools. Nevertheless, some studies found that the concentrations of cat and dog allergens in dust within schools were above the levels associated with development of allergen sensitization, i.e., above the levels that cause susceptible people to become reactive to the allergens [1-3].
Concentrations of dust mite allergen in floor dust samples from schools have usually been less than concentrations in samples of floor dust from homes [2, 3, 5, 6]. In most cases, concentrations of mite allergens in dust from schools has been lower than the concentrations associated with sensitization to dust mite allergen from research in homes [1, 2]. Dust mites thrive in higher humidity environments and higher dust mite allergen concentrations have been reported from humid climates [1, 2, 7].
Fewer data are available on concentrations of cockroach allergen in dust from schools and concentrations vary greatly among schools and among locations within schools . Concentrations appear to be higher in inner-city and rural U.S. schools relative to other schools . Also, concentrations tend to be highest near food sources such as kitchens and cafeterias [1, 2]. In one review, five of ten studies reported average cockroach allergen concentrations in schools above the level associated with development of allergic sensitization . Another review concluded that all median or mean concentrations were below the level associated with exacerbation of asthma .
Data on concentrations of mouse allergen in dust from schools are very limited. As with cockroach allergen, there is much variability among and within schools, with evidence of higher concentrations in inner-city and rural schools . A study in the U.S. found higher concentrations of mouse allergen in dust from inner-city schools than in dust from homes . In a study of 11 urban schools in the U.S., many of the measured concentrations exceeded the concentrations associated with development of allergic sensitization .
Few studies have investigated associations of concentrations of allergens in schools with adverse health effects. A Swedish study of 410 cat-allergic children with asthma and no cat at home found decreased peak expiratory flow (a measure of lung function), a nine-fold increase in days with asthma symptoms, and increased asthma medication use in students within classrooms that had more than the median level of cat owners . In each case, the increase was statistically significant. Another Swedish study  of eight schools found increases in respiratory symptoms associated with increased cat allergen concentrations, but the increases were not statistically significant. The same study found statistically significant increases in wheeze and daytime breathlessness associated with higher dog allergen concentrations and statistically significant increases in wheeze, daytime breathlessness, current asthma, and allergic sensitization associated with higher concentrations of horse allergen in dust. A third Swedish study of 39 schools found a statistically significant increase in prevalence of asthma diagnosis associated with increased cat allergen in dust, but not with increased dog or mite allergen . A German study of 1893 school children  found that sensitivity to (being allergic to) cat allergen in children with no regular contact with cats increased in a dose-response manner with the percentage of classmates and school mates reporting regular cat contact. The trends were statistically significant. A study of 12 schools in the eastern U.S. , found statistically significant increases in asthma prevalence rates associated with higher levels of cockroach allergen in dust, but not with higher concentrations of cat, dog, or dust mite allergens. Together, this body of research suggests adverse allergy and asthma outcomes are associated with increased cat allergens at school. For other allergens, data are too limited for any conclusions.
In summary, concentrations of pet allergens in dust from classrooms are often higher than concentrations in dust from homes without pets. Concentrations of allergens from pets, cockroach, and mice in the dust of classrooms often exceed the levels associated with development of allergic sensitization in homes. Available data suggest an association of adverse allergy and asthma outcomes with increased cat allergen in schools. Pet allergen is transported into classrooms on the clothes of children with pets at home. Other than prohibiting pets at school, there may be no viable options for school personnel to reduce the sources of these allergens in schools. Improved space cleaning will likely help reduce concentrations of these allergens in classrooms, but the effectiveness of cleaning has been inadequately studied. Measures likely to reduce cockroach and mouse allergens in schools include better housekeeping and building maintenance and integrated pest management practices. A study of 13 U.S. schools  found that integrated pest management for cockroach control, which corrects conditions conducive to cockroach infestation and uses cockroach traps and minimal pesticides, was more effective than conventional pest control focusing on routine use of pesticides. Improvements in particle filtration may help to reduce airborne concentrations of allergens but the effectiveness of filtration for allergens in schools has been little studied. More information on filtration is available in the section of this web site on air cleaning.