Abstract
There are a number of risk factors for the development of asthma, including genetic and environmental components. Moreover, there is mounting evidence that a variety of genes are associated with the features of asthma, such as persistent wheezing, airway responsiveness and chronic bronchial inflammation. However, for expression of these features, other factors must also come into play. This paper focuses on the importance of environmental factors in the development of asthma, including allergens and respiratory infections. From current evidence, it appears that in subjects with the appropriate genetic make-up, infections and allergens induce a proinflammatory cytokine response that causes airway inflammation and that in turn leads to the initiation and persistence of altered airway function.