Atopy is defined as the production of specific IgE in response to exposure to common environmental allergens, such as house dust mite, grass, and cat. Being atopic is strongly associated with allergic disease such as asthma, hay fever, and eczema, but not everyone with atopy develops clinical manifestations of allergy and not everyone with a clinical syndrome compatible with allergic disease can be shown to be atopic when tested for specific IgE to a wide range of environmental allergens. This is particularly so for asthma.

Asthma is arguably the most serious of the allergic diseases in that it is disabling (causing more than 100 000 hospital admissions each year in England and Wales) and occasionally fatal. In 1995, 137 people aged under 45 died as a result of asthma. Although concern has been expressed that death certificates may overestimate or underestimate asthma mortality depending on diagnostic fashion, significant misclassification with other forms of chronic obstructive lung disease in this age group is unlikely. In the early 1960s asthma mortality increased dramatically in many countries. The increase was attributed to the excessive use of non-selective β agonists, which were subsequently withdrawn from the market. More recent increases in asthma mortality reported from Britain, France, and the United States may be related to increased prevalence or severity of asthma or inadequate health care. Evidence for the latter comes from audits and confidential inquiries that show inadequate treatment of asthma in the months leading up to death and during the fatal attack and the observation of higher mortality in populations recognised as often receiving poor health care (socioeconomically deprived people in Britain; black people in the United States). …