Since indoor allergen exposure was shown to be associated with allergic sensitization, which on the other hand was associated with childhood asthma, it was understandable that the first intervention studies aiming at primary prevention of early sensitization and the development of allergic airway disease have concentrated on indoor allergen avoidance.
The earliest trial, the Isle of Wight study, showed that children at the age of 8 years tended to have less wheeze and a lower risk for mite sensitization following the avoidance of early house dust mite allergen contact. In contrast, the Study of Prevention of Allergy in Children in Europe (SPACE) was not able to show a significant benefit in the intervention group (mattress covers).
In the Manchester Allergy and Asthma Study (MAAS), 291 infants—at high risk because both parents were atopic and there were pets in the home—were recruited, and a number of avoidance measures were instituted to decrease inhalant allergen exposure. The group was able to demonstrate that the avoidance measures were capable of achieving and maintaining a low dust allergen environment during pregnancy and for the first 3 years of these children. At age 3 years, children in the active group had less wheeze and a lower airway resistance; however, the sensitization rate to mites was higher than that in the control group In the Dutch Prevention of Incidence of Asthma and Mite Allergy (PIAMA) study, the intervention had a significant effect on mite allergen levels, but no effect was seen on respiratory symptoms, atopic dermatitis, or total and specific immunoglobulin E levels.
So far, we must admit that recommendations to families for primary prevention of asthma should be given with caution, as no single approach can definitively prevent children from developing asthma.