Relations between childhood asthma and environmental factors

The current rise of asthma prevalence could be partly explain by environmental factors. The outdoor pollution does not create asthma but can increase its severity when asthma is present. The responsibility of the indoor pollution and especially of the environmental tobacco smoke is more important. Passive smoking can induce and increase asthma severity particularly when children are young, House dust mites sensitisation is a major risk factor for the development of asthma in children. The severity of asthma symptoms vary with the level of exposure and the elimination of exposure to house-dust mites is able to produce a remarkable reversal of asthma in sensitive children. However childhood farm environment and early exposure to pets at home, seems to have a protective effect against asthma and wheezing. Possible explanations for the lower prevalence of asthma in these children might be the development of immunotolerance or the stimulation of TH1 cells and suppression of TH2 cells by increased exposure of farm children to microbial antigens in the stables or farmhouses, But, when asthma and sensitisation are present, it is always necessary to avoid the contact with cats and dogs. (C) 2002 Editions scientifiques et medicales Elsevier SAS.