Introduction

Asthma is a common disease worldwide with significant ethnic and regional variations. An increasing morbidity and mortality, as well as health care burden from asthma has been recognized lately.1 There has been a change in the epidemiology and clinical spectrum of asthma with an apparent increase in the overall prevalence along with a rise in the incidence of 'difficult to treat' cases. Atopy, the production of abnormal amounts of IgE antibodies in response to common environmental allergens, is the strongest identifiable predisposing factor for developing asthma. Associations of asthma with infections, air pollution, tobacco smoke and other agents have been proposed but some of the risk factors are a subject of debate about their causal relationship with asthma.