Allergy is the most common chronic disease among children and young adults in Sweden today. Allergies are scarce among the population in poor countries and among children who grew up on farms with animal husbandry. In this project, we investigate which lifestyle and environmental factors are associated with protection against allergy development. Our aim is to provide a science-based strategy to protect future children from developing allergy. In particular, we focus on three approaches: - Stimulation of the infant's immune system through natural exposure to a complex oral flora - Intake of fats that attenuate the propensity of the immune system to elicit allergic immune responses - Development of an allergy "vaccine" based on bacterial "superantigens" that stimulate the infant's immature immune system and support tolerance development. Our studies are based on carefully followed birth cohorts where lifestyle factors, diet, gut microbiota and immune response are recorded and analyzed in relation to allergy development, as well as relevant animal models to study the mechanisms at work. We believe that our approach can lead to the development of effective strategies to curb the allergy epidemic that is plaguing the Western world and which also affects the population of countries where economic development is accelerating and living conditions are improving.