Asthma and allergies: The role of the home environment

The incidence of asthma and allergy has increased throughout the developed worldover the past forty years (1). The incidence is much higher for children than adults.From being a relatively uncommon disease, a few decades ago, allergies today, inmany regions, are affecting a large part of the population. The European AllergyWhite Paper (1997) noted that with the exception of AIDS, only few diseases, besidesallergies, have increased two- or three-fold within a short time (2). Allergic diseasesare supposed to be caused by a complex interaction between genetic andenvironmental exposures. The temporal trends in allergy prevalence, the differencesin the risk of allergy between urban and rural populations of the same ethnicity andthe short time period for which the prevalence of allergic diseases have increased,indicate that changes in environmental exposures rather than genetic factors are themost likely explanation for the increase (3, 4).But, what changes in environmental exposures are important for the increase inallergies?In the search of causative factors its important to note that small children areparticularly at risk. Thus the exposure during pregnancy and first years of life seemsmore important than exposure later in life. Children have a higher metabolism andfaster respiratory rate compared to adults resulting in higher intake of food, drink andair per unit of body volume, i.e. higher dose which is further enforced by their handto-mouth behaviour. The exposure (in mass) during pregnancy is defined by theexposure of the mother, while the exposure of babies mainly consist of indoor air(around 80%), and food, mainly breastmilk. In developed countries more than 50 % ofthe total exposure (in mass), during a 70 year life consists of air in the home, whileoutdoor air, food and liquids, and industrial air stands for around 7% each. The rest ofthe exposure is air in schools, day care, offices, and during travelling. This review is based on multidisciplinary state-of-art reviews of the scientificliterature on associations between indoor exposures and asthma and allergies (6, 7, 8,9), and on results from two ongoing studies in Sweden and Bulgaria, DBH, andALLHOME. The studies in Sweden and Bulgaria are basically identical, starting witha cross-sectional questionnaire study on small children, allergic manifestations andhome environmental factors. The second step has been nested case-control studiesincluding clinical examinations, inspections and environmental measurements.