Do allergens play a role in early childhood asthma?

What we know: Sensitisation to indoor allergens (house-dust mite, cat) is related to the level of exposure to these allergens in early childhood. The prevalence of asthma in childhood is independent of allergen exposure in early life. Asthma occurs in a substantial number of young children in the absence of allergen sensitisation. Asthma and allergic sensitisation have increased in recent decades, but there is no conclusive evidence that this is due to changes in environmental allergens. What we need to know: Have changes in environmental allergens contributed to the increasing incidence of asthma in recent decades? Is early childhood asthma (or certain subtypes of asthma) an allergen-induced disease? Is it possible to modify asthma by environmental allergen manipulation in early childhood? Is it possible to modulate the immune response to allergens in a favourable direction in early childhood?