Asthma symptoms and airway narrowing in children growing up in an urban versus rural environment.

The development of asthma and allergy appears to be the result of gene-environment interaction. Potential environmental risk factors such as outdoor and indoor air pollution, infections, allergen exposure, diet, and lifestyle patterns may trigger respiratory symptoms and compromise lung function in children. Specific features of urban and rural lifestyle may constitute distinct risk factors but may also coexist within certain socioeconomic levels. Children of rural environments are at lower risk for asthma and aeroallergen sensitization. The protective effect has been associated with close contact with large animals, but the genetic factor also plays a contributory role. Children with prolonged exposure to urban environment are at increased risk of reduced lung function and those that reside in polluted areas exhibit slower lung growth. It is possible that polluted urban environment per se facilitates subclinical small airway disease. Evidence to date supports a strong relation between residential area as a potential risk factor for childhood asthma symptoms and airway obstruction and a western type of socioeconomic development.