Environmentally induced asthma.

Asthma is characterized by inflammation, reversible airway obstruction, and increased airway responsiveness to various stimuli. Despite advances in understanding of the pathophysiology and in developing new treatments, asthma prevalence and mortality have been rising over the last decade, after a steady decline in the 1970s. Risk factors for environmentally induced asthma include air pollutants, tobacco smoke, wood smoke, and excessive allergen exposure. In controlled human chamber studies, asthmatics demonstrate increased susceptibility to outdoor pollutants such as sulfur dioxide, nitrogen dioxide, and acidic particles with acute reductions in lung function during and following exposures; responses are enhanced by increased ventilation, for example during exercise, or breathing cold air and/or dry air. The evidence is even stronger that inhaled indoor allergens have a causal relationship to asthma. It is possible that changes in housing conditions have led to increased levels of dust mite and other proteins in homes with consequent increases in the prevalence of sensitization. Avoidance of specific allergens such as house dust mite over months results in a reduction in clinical symptoms and bronchial hyperresponsiveness. The interaction between aeroallergens and air pollutants in triggering environmentally induced asthma is an area of active research.