In my project, I study the link between allergy development and food factors. Allergies are a growing disease that currently affects 25% of adults and children in Sweden. One explanation for the increasing proportion of allergy in the Western world could be changing dietary habits. The most compelling link between diet and allergy development is that between the early introduction of fish and reduced incidence of eczema in children, this coupling is speculated to depend on the long polyunsaturated fatty acids, omega-3 fatty acids, found in fish. Vitamin D is another substance that has been studied much in relation to allergy development. The purpose of this PhD project is to find out how polyunsaturated fatty acids and fat soluble vitamins affect allergy development. This is done partly by studying the levels of these substances in the blood from allergic and healthy children. In addition, animal models are used to look at the underlying mechanisms.