Review of hay fever. 1. Historical background and mechanisms.

This is the first of two review articles about hay fever. The historical background of hay fever, including 'rose fever' in the fifteenth and sixteenth centuries, and the discovery of immunoglobulin E is described. The second section deals with the botanical aspects, aerobiology, climate and topography and geographical differences. Next, the prevalence of hay fever in the community, its natural history and age--sex incidence are considered. The influence of hereditary factors, time of birth and the relationship of hay fever to asthma are also dealt with. The role of the relevant aeroallergen, pollen characteristics and chemistry and allergen exposure lead logically to a description of our current understanding of the type 1 immune reaction. The second article will deal with clinical features, diagnosis and investigation, and treatment.