Objectives: We studied the association between early life conditions and asthma in adolescence.
Methods: We conducted a population-based birth cohort study involving 2250 male 18-year-olds residing in Brazil.
Results: Approximately 18% of the adolescents reported having asthma. Several childhood factors were found to be significantly associated with increased asthma risk: being of high socioeconomic status, living in an uncrowded household, and children being breastfed for 9 months or longer.
Conclusions: The present results are consistent with the "hygiene hypothesis," according to which early exposure to infections provides protection against asthma. The policy implications of our findings are unclear given that risk factors for asthma protect against serious childhood diseases in developing countries.