How much asthma is really attributable to atopy?

In recent decades it has become routine to describe asthma as an atopic disease. A theoretical paradigm has evolved in which allergen exposure produces atopic sensitisation and continued exposure leads to clinical asthma through the development of airways inflammation, bronchial hyperresponsiveness, and reversible airflow obstruction. As Martinez 1 notes, this paradigm has been used with particular insistence with regard to house dust mite allergens, 2 3 but other allergens (cat, cockroach, dog) are also believed to be important. The importance of atopy is most widely accepted for asthma in children whereas, among adults, asthma has traditionally been divided into "extrinsic" and "intrinsic" asthma, although this also has been challenged. It is acknowledged that not all cases of asthma fit this paradigm-for example, some occupational causes of asthma do not appear to involve atopy-but these are regarded as interesting minor anomalies that do not threaten the dominant paradigm.