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Indoor Allergens

The following extracts are taken from an academic allergy book that I have in my collection, titled ‘Indoor Allergens – Assessing and Controlling Adverse Health Effects’ written by the Committee on the Health Effects of Indoor Allergens, Division of Health Promotion and Disease Prevention, Institute of Medicine (1993)


The role of allergen avoidance is a primary method of promoting good health and controlling diseases that are initiated or exacerbated by exposure to indoor allergens. For example, as decided previously in this report, avoidance is considered an important method of treatment for dust mite allergy (Buckley and Pearlman, 1988; Melan, 1972) and is also associated with improvement of asthma when rigorous methods of avoidance are employed (Murray and Ferguson, 1983; Platts-Mills et al., 1982).

Central to the hypothesis that education about allergen avoidance reduces morbidity of respiratory diseases such as asthma is the demonstration of threshold levels of exposure to common indoor allergens in individuals at risk. Recent progress in the immunochemical detection of common indoor allergens such as those associated with cats and dust mites makes it possible to estimate exposure to these allergens and to begin to define threshold levels of exposure that will cause sensitization and increased symptoms. The example given earlier in this report describes the case of dust mites and the fact that researchers have suggested that exposure to greater than 2 micron-grams of Der p I mite allergen (or 100 mites)/g of dust increases the risk that children will develop sensitization and asthma (Platts-Mills et al., 1991a). In a prospective study in a cohort of British children at risk of allergic disease because of family history, Sporik and colleagues (1990) reported a trend toward sensitization to dust mite allergen by age 11 with exposure at age 1 to more than 10 micron-grams of Der p I/g of dust. The age at which wheezing first occurred was inversely related to the level of exposure at age 1 for those children who became sensitized.

These reports suggest strongly that in addition to genetic factors, exposure to certain allergens in early childhood is an important determinant of subsequent development of respiratory diseases such as asthma. If this is indeed the case, avoidance of indoor allergens and the role of education in promoting avoidance measures in the general public must necessarily assume a high priority.

Education is an important component in the prevention and control of allergen-induced diseases. Considering that a large percentage of hospital admissions for asthma can be prevented by educating physicians and patients in the proper control measures, the need for emphasis on education becomes obvious. By disseminating information to physicians, to health care providers, to patients, and to building design, construction and operations professionals, prevention of diseases associated with indoor allergens becomes not only realistic, but may offer a cost-effective means of reducing morbidity.


In developing and implementing educational interventions, consideration should be given to identifying populations such as those with severe asthma who are more motivated and more likely to benefit from intervention.

Recommendation: Identify population groups most likely to benefit from educational and allergen-avoidance interventions. This effort should be based on an understanding of what allergens serve as risk factors for different individuals.

Socioeconomic, educational, and ethnic characteristics are important variables that should be considered in developing effective educational intervention programs. Programs that focus on these factors in tailoring self-management programs should greatly enhance both the acquisition and the performance of self-management competencies.

Recommendation: Develop focused educational programs for allergic populations with different socioeconomic and educational characteristics.


Research indicates that of those persons with asthma 90% of children, 70% of young adults, and 50% of older adults also have allergy (Lehrer et al., 1986; Peat et al., 1987; Platts-Mills et al., 1992). These data strongly suggest a role for allergy in the pathogenesis of asthma, particularly in childhood.

…the observation that allergy often develops by age 5 suggests that interventions are needed for infants and young children.

Three common diseases are clearly related to exposure to indoor allergens: asthma, rhinitis (hay fever), and allergic skin conditions (i.e., eczema and urticaria). Although specific causal genes have not been identified, the genetic predisposition for these diseases is well established. If neither parent has a history of allergy or atopy, a child has only a 0-19% chance of having a childhood allergic disease. If one parent has atopy, the risk rises to 31-58%; if both parents have atopy, the risk rises still further to 60-100% (Zeiger, 1988). In addition, an earlier age of onset of allergic disease is related to a family history of atopy (Figure 2-5; Smith, 1988).

Early childhood is a common time for sensitization. Barbee and others (1987) showed that 22% of a cohort of children less than 5 years old had skin test reactivity to one or more allergens. During an 8-year follow-up, the prevalence increased to 44%. Gergen and co-workers showed that 18% of Caucasian and 28% of African American children showed skin test reactivity when tested between the ages of 6 and 11 (Gergen et al., 1987). In a cohort of genetically susceptible children, 20% developed skin test reactivity by age 5; another 20% became reactive between ages 5 and 11 (Sporik et al., 1990).

Although most studies investigate asthma (because it is common and can be measured objectively), sensitivity to indoor allergens is also very common among patients with other allergic conditions such as chronic rhinitis and atopic dermatitis. Because the important cause of inflammation that is common for all of these diseases is exposure to allergens, avoidance of the exposure should be the primary anti-inflammatory treatment. Developing realistic avoidance protocols for routine use is a challenge that must not take second place to pharmaceutical treatment.

With most people spending the great majority of their time indoors – and most of that in their own houses – it is not surprising that the bulk of inhaled foreign protein is associated with indoor air. The evidence shows that a large proportion of asthmatics are allergic to indoor allergens and that several changes in the way we live indoors may have affected the levels of these allergens. These changes include increased mean temperatures, reduced ventilation (with consequent increased humidity), fitted carpets, and cool-wash detergents which have led to water temperatures for washing bedding that do not kill mites.

Once identified, reducing exposure to allergenic ""trigger factors"" has been a standard part of the treatment of allergic disease for many years. Since approximately half of existing cases of asthma have been attributed to allergenic factors, it is reasonable to expect that asthmatics who require more than occasional treatment might also have allergies that induce their asthma.


In keeping with a public health approach to prevention and control of allergic disease and the need to improve the understanding of the etiology, it is important to identify potential risk factors associated with allergic disease. Risk factors are biological, environmental, and behavioral characteristics that are causally associated with health-related conditions (Lalonde, 1974; Last, 1986).

Exposure to allergens is an example of an environmental risk factor related to the prevalence of sensitization. Household exposure to elevated levels of dust mite allergen in infancy, for example, has been associated by age 5 with an increased prevalence of positive dust mite skin tests and an increased concentration of dust mite IgE antibody (Zeiger, 1988).


Reducing exposure to so-called ""trigger factors,"" i.e., factors that trigger an allergic response, has been a standard part of the treatment of allergic disease for many years, and for many years it was normal practice to recom¬mend avoidance measures to patients who had skin tests that were positive for house dust. This practice was strongly supported by the experiments of Storm van Leeuwen (Storm van Leeuwen et al., 1927) and Rost (1932), who demonstrated benefits to patients with asthma and atopic dermatitis, respectively, from living in a ""climate chamber.""

Until recently, there has been only limited clinical use of avoidance measures in treating allergic diseases associated with dust mite sensitivity, in part because the control measures that were originally proposed were not effective in controlling mite allergens (Burr et al., 1980; Korsgaard, 1982). In addition, several general medical tests have suggested that avoidance measures should be considered in patients who have a certain typical history. As discussed earlier, however, many allergic patients are not aware of an association between dust exposure and their symptoms (particularly the association between dust and asthma or atopic dermatitis). Today, there is considerable evidence that full avoidance (i.e., 95% reduction of mite allergen) can be achieved and can reduce both symptoms and bronchial reactivity. For example, moving patients to a hospital room or sanatorium has been consistently effective (Dorward et al., 1988; Ehnert et al.,- 1991; Platts-Mills et al., 1982; Warner and Boner, 1988); these units generally have very low levels of mites (i.e., less than 20 mites/g of dust) and mite allergen (less than 0.4 micron grams of Der p I/g). Recently, four controlled studies of the effects of avoidance measures conducted in the homes of patients have found significant improvement in both asthma symptoms and bronchial hyperreactivity (Dorward et al., 1988; Ehnert et al., 1991; Murray and Ferguson, 1983; Walshaw and Evans, 1986).

Avoidance measures can be divided into those for use in the bedroom and those for use in the rest of the house. In the bedroom, the following have been shown to be effective: covering mattresses and pil¬lows with impermeable covers; washing bedding at 130°F once per week. (Miller et al., 1992; Owen et al., 1990); and removing carpets (although Rose and colleagues [1992] have shown that the use of acaricides or tannic acid treatment can also reduce mite allergen). Other control strategies for the bedroom are designed to eliminate sites in which mites can grow and to reduce dust collectors to make cleaning easier. The recent report from NHLBI (1991) is an excellent source of information regarding allergen avoidance.

Three different approaches are possible for control of mite growth in the rest of the house:

1. Design the house with polished floors and wooden, vinyl, or leather furniture to eliminate sites where mites can grow.

2. Maintain indoor relative humidity at below 50% (absolute hu¬midity below 6 g/kg). Korsgaard (l983a) has shown that in some areas of the world this can be accomplished by simply increasing ventilation. In other areas, it would be necessary to use air conditioning during the humid months.

3. Use acaricides to treat carpets or furniture, including pyrethroids (D.

Charpin et al., 1990b), natamycin (an antifungal), pirimiphos methyl (Mitchell et al., 1985), and benzyl benzoate (Bischoff et al., 1990). In each case the chemicals are effective in killing the mites, although methods for applying the agents may present problems (de Saint-Georges-Gridelet et al., 1988; Platts-Mills et al., 1992).

Several different chemical treatments have been shown to achieve 90% reduction in allergen levels for a month or more. In addition, 1 or 3% solutions of tannic acid have been recommended for denaturing mite allergens (Green et al., 1989). Again, this method achieves a 90% reduction of mite allergen, but because tannic acid does not kill mites, the effect is temporary (i.e., approximately 6 weeks to 2 months). Carpets fitted onto unventilated floors-for example, in basements or on the ground floor of a house built on a concrete slab-are particularly difficult to treat. Under these circumstances water can accumu¬late either because of condensation onto the cold surface of the concrete or because of leakage (either domestic or rainwater from outside). In either case, once the carpet is wet, it will stay wet and become an excellent envi¬ronment for the growth of fungi and mites.

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