the prevalence and severity of asthma has increased in the last 20 years , and the greatest increase has been seen among children and young adults living in u.s . 
 inner cities . 
 the reasons for this increase are obviously complex , but include environmental exposures to allergens and pollutants , changing patterns of medication , and the psychosocial stresses of living in poor inner - city neighborhoods . 
 this paper presents an overview of environmental , immunologic , and genetic factors associated with asthma morbidity and mortality . 
 this overview can be used to provide a framework for designing an interdisciplinary research program to address the complexities of asthma etiology and exacerbation . 
 the strongest epidemiologic association has been found between asthma morbidity and the exposure of immunologically sensitive asthmatic patients to airborne allergens . 
 our current understanding of the process of sensitization suggests that there is a strong genetic predisposition to form ige to allergenic proteins on airborne particles . 
 much of this work has been conducted with animal models , but in a number of instances , specific confirmation has been reported in humans . 
 sensitized individuals respond to inhaled exposure with immediate mast - cell dependent inflammation that may be augmented by pollutant particles , especially diesel exhaust particles . 
 relatively little is known about the methods of assessing exposure to airborne pollutants , especially biologically active particulates . 
 however , to examine the relationship of morbidity in genetically predisposed individuals , it will be important to determine the most relevant method of making this assessment.imagesfigure 2figure 3figure 4figure 5figure 6