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The aim of this article is to provide information on risk factors associated with the development of atopy and asthma in childhood.Several gene polymorphisms have been associated with susceptibility to asthma and allergy; complex gene–environmental interactions, however, appear to play a key role in the development of the disease. Early life sensitization to aeroallergens, presence of atopic dermatitis or allergic rhinitis, maternal smoking during pregnancy and children's environmental exposure to tobacco smoke, lower respiratory tract infections with respiratory syncytial virus and potentially with other viruses including rhinovirus and metapneumovirus, exposure to air pollutants, several perinatal factors other than maternal smoking, are among factors associated with an increased risk for development of chronic asthma.The prevalence of asthma and allergic diseases is increasing progressively. Those who are involved in the care of young children should be prepared to recognize risk factors for development of these diseases and to appreciate the role of gene–environment interactions. Preventive measures established at an early age may modify the natural history of asthma and other allergic diseases.