Background: Reduced lung function is a feature of chronic asthma, which becomes apparent at school age. Unknown factors between birth and school age determine the progressive loss of pulmonary function in children with persistent asthma. We investigated the role of allergic sensitisation and allergen exposure early in life.

Methods: The German Multicentre Allergy Study followed 1314 children from birth to 13 years of age. We regularly interviewed parents about their child's asthma and measured IgE levels. Allergen exposure was assessed at age 6 months, 18 months, and at 3, 4, and 5 years; lung function was assessed at 7, 10, and 13 years; post-bronchodilator response at 10 and 13 years; and a bronchial histamine challenge was done at 7 years.

Results: 90% of children with wheeze but no atopy lost their symptoms at school age and retained normal lung function at puberty. By contrast, sensitisation to perennial allergens (eg, house dust mite, cat and dog hair) developing in the first 3 years of life was associated with a loss of lung function at school age. Concomitant exposure to high levels of perennial allergens early in life aggravated this process: forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) ratio was 87.4 (SD 7.4) for those sensitised and with high exposure compared with 92.6 (6.0) for those not sensitised, p<0.0001; and maximal expiratory flow at 50% (MEF50) 86.4 (25.1) for sensitised and with high exposure compared with 101.5 (23.2; p=0.0031) for those not sensitised. Such exposure also enhanced the development of airway hyper-responsiveness in sensitised children with wheeze. Sensitisation and exposure later in life had much weaker effects and sensitisation to seasonal allergens did not play a part.

Interpretation: The chronic course of asthma characterised by airway hyper-responsiveness and impairment of lung function at school age is determined by continuing allergic airway inflammation beginning in the first 3 years of life. However, children with a non-atopic wheezing phenotype lose their symptoms over school age and retain normal lung function at puberty.