The role of environmental factors in asthma

Although the everyday experience of asthmatic patients provides ample anecd otal evidence that environmental exposures provoke bronchospasm, it has pro ved more difficult to assess the impact of air quality on the timing of ast hma attacks and the prevalence of asthma in populations. Spectacular 'asthma epidemic days' are sometimes attributable to exceptiona l outdoor aero-allergen exposures. By comparison, effects of inorganic part icles and gaseous pollutants in outdoor air on the incidence of asthma atta cks are subtle and poorly quantified. Environmental tobacco smoke and mould growth are the indoor factors most co nsistently associated with respiratory morbidity, but their roles in initia ting allergic asthma remain uncertain. Evidence relating asthma risk to fum es from gas cooking, and to allergens from dust mites and household pets re mains confused and controversial. It is unlikely that trends in either outdoor or indoor air pollution have c ontributed substantially to the rise in prevalence of asthma and allergic d isease in recent decades.