To cite this article: Anto JM, Sunyer J, Basagana X, Garcia-Esteban R, Cerveri I, de Marco R, Heinrich J, Janson C, Jarvis D, Kogevinas M, Kuenzli N, Leynaert B, Svanes C, Wjst M, Gislason T, Burney P. Risk factors of new-onset asthma in adults: a population-based international cohort study. Allergy 2010; 65: 1021-1030 Abstract Background: The occurrence of new-onset asthma during adulthood is common, but there is insufficient understanding of its determinants including the role of atopy. Objective: To assess the risk factors for the development of new-onset asthma in middle-aged adults and to compare them according to atopy. Methods: A longitudinal analysis of 9175 young adults who participated in two surveys of the European Community Respiratory Health Survey (ECRHS) conducted 9 years apart. Findings: We observed 179 cases of new-onset asthma among 4588 participants who were free of asthma and reported at the beginning of the follow-up that they had never had asthma (4.5 per 1000 person-years). In a logistic regression, the following risk factors were found to increase the risk of new-onset asthma: female gender (OR: 1.97; 95% confidence interval (CI): 1.38,2.81), bronchial hyperresponsiveness (3.25; 2.19,4.83), atopy (1.55;1.08,2.21), FEV(1) < 100 % predicted (1.87;1.34,2.62), nasal allergy (1.98;1.39,2.84) and maternal asthma (1.91;1.13;3.21). Obesity, respiratory infections in early life and high-risk occupations increased the risk of new-onset asthma although we had limited power to confirm their role. Among the atopics, total IgE and sensitization to cat were independently related to the risk of new-onset asthma. The proportion of new-onset asthma attributable to atopy varied from 12% to 21%. Conclusion: Adults reporting that they had never had asthma were at a substantial risk of new-onset asthma as a result of multiple independent risk factors including lung function. Atopy explains a small proportion of new-onset adult asthma