The prevalence of allergic diseases, including asthma and hay fever (allergic rhinoconjunctivitis), has increased in developed countries around the world during the past decades and continue to increase. According to the American Academy of Allergy Asthma and Immunology, allergic diseases currently affect more than 25% of individuals in the USA. This has impacted the global allergy market.
Many studies suggest that exposure to common indoor allergens is a relevant environmental factor partially responsible for the increase in prevalence of allergic diseases in developed countries. Individuals in these countries spend more than 90% of their time indoors, and therefore exposure to indoor allergens is prolonged. Genetically susceptible individuals exposed to indoor allergens, primarily during infancy, become sensitized to these allergens.
Allergen avoidance can prevent (to some extent) the development of sensitization to allergens and relieve allergic symptoms in allergen-sensitized individuals. Therefore, various medical and public-oriented professional organizations have emphasized the relevance of indoor allergen exposure and recommended several guidelines for affected subjects, encouraging the use of certain measures for optimal indoor allergen avoidance.
Several multi-center studies on asthma and allergens performed at the national level in homes of affected subjects (including the National Cooperative Inner-City Asthma Study and the National Survey of Lead and Allergens in Housing) have demonstrated the usefulness of allergen measurement in monitoring the efficacy of allergen avoidance interventions.
The high prevalence of allergies has contributed to the increased public concern about air quality in homes, schools, and the workplace during the past years. However, due to the growing demand for mold assessments, common allergens (other than fungi) are not typically addressed during the course of indoor air quality inspections, albeit these non-fungal allergens are often the cause of the allergy symptoms experienced by building occupants.
A number of allergens are present indoors. A dose-response relationship between exposure and sensitization has been described for dust mite, cockroach, cat, and dog allergens. Cat and dog allergens are contained in small particles (2-6 um in diameter), which are passively transported to public buildings. Therefore, cat and dog allergens are ubiquitous and present in the majority of buildings, including those where these animals have never been housed, like new homes and schools, at levels that, in some cases, exceed proposed thresholds to cause sensitization.
Studies performed in several major inner cities of the USA have linked exposure to cockroach, rat, and mouse allergens with asthma, and indicate that these allergens account for 95% of the allergen load present in some homes.
The relevance of indoor allergen exposure during infancy to cause sensitization and development of asthma should be emphasized to the general public. Daycare centers and schools can be critical sites of exposure to indoor allergens, and it has been suggested that these buildings should be target locations for interventions. Epidemiologically, it can be more effective to target one single daycare center or school than multiple homes.