Allergy, asthma and the environment: an introduction.

In Europe and the USA the prevalence of certain forms of allergic disease is rising; an increase that can not be reconciled simply on the basis of changes in diagnostic fashion. The changes observed have been too rapid to be explained by alterations in the gene pool and, as a consequence, there has been a growing interest in the possible associations between environmental factors, allergic disease and asthma. Among the environmental influences that have been implicated in modifying the development of respiratory allergy and asthma are the conditions of exposure to allergens themselves, indoor air quality, outdoor air pollution, tobacco smoking, diet and infectious disease. The contributions of some of these factors, acting alone or in concert, to the development of allergic disease are considered.