Much of what is known about asthma risk factors comes from studies of young children. Risk factors for the development of asthma in adults, particularly de novo in adults who did not have asthma in childhood, are less well defined. The lack of a clear definition for asthma presents a significant problem in studying the role of different risk factors in the development of this complex disease, because the characteristics that define asthma (., airway hyperresponsiveness, atopy, and allergic sensitization) are themselves products of complex gene-environment interactions and are therefore both features of asthma and risk factors for the development of the disease. Host Factors Genetic. Asthma has a heritable component, but it is not simple
