[Prevention of allergic diseases in childhood: from theory to reality].

Allergic diseases have an increasing worldwide prevalence and a great impact on the health related costs. The research is focused on the study of etiological and risk factors of allergic diseases that can potentially be modified with primary, secondary and tertiary prevention strategies. Many of these measures do not have a definitively proven effect taking place in a controlled context different to what happens in real life. This paper aims to review the latest evidence on prevention of allergic diseases considering certainties and unresolved issues and focuses mainly on environmental, dietary, pharmacological and immunological preventive strategies for different levels of prevention. It is imperative to have a better understanding of genetic and environmental factors that cause allergic diseases to optimize preventive measures that are effective in reversing the increasing trend in the prevalence of allergic illnesses in childhood.