[Hypothesis of the changes in the frequency of asthma].

Review of the literature reveals sporadic but true increases in the prevalence and death rates for asthma over the past 25 years. Although changes in hereditary, allergic and environmental factors must be considered as possible causes of this increase, its suddenness points to risk factors that change rapidly. Such is the case with atmospheric pollutants, notably nitrogen dioxide and particles, both of which have been shown to have adverse effects on the tracheobronchial tree. These pollutants tend to concentrate inside homes, especially since the early 1980s, when the energy crisis brought about changes in the home environment.