Epidemiology of the relationship between exposure to indoor allergens and asthma.

A very high prevalence of immediate hypersensitivity to common indoor allergens can be demonstrated among children and young adults, with asthma. Recent progress in the immunochemistry of cat, dust mite and cockroach allergens has made it possible to measure exposure to these allergens and to start to define threshold levels of exposure which increase the risk of sensitization and symptomatic asthma. Indeed, it is already clear that exposure to greater than 2 micrograms group I dust mite allergen (or 100 mites) per gram of dust increases the risk of children developing sensitization and asthma. Furthermore, from studies on patients presenting to emergency rooms with asthma, it is clear that the risk of sensitization to allergens derived from cats or cockroaches or grass pollen is restricted to patients who are exposed to high levels of these allergens. Given the increasing morbidity and mortality of asthma it is clear that therapeutic efforts should be focused on identifying relevant allergens and advising patients about techniques for reducing exposure.