Immune system activation and inflammation are deeply involved in the pathogenesis of a variety of diseases including infections, autoimmunity and malignancy as well as allergy and asthma. The incidence of allergy and asthma has significantly increased during the past decades. Still the background of this phenomenon is not well understood. The contribution of life style and habits are heavily discussed. Among them is a too clean environment which may predispose individuals to an increased sensitivity to allergic responses. Also dietary habits have changed drastically in the Western world, and it appears that especially the increased use of antioxidant food supplements, preservatives and colorants could be of relevance. In vitro experiments show that typical antioxidant compounds like vitamin C and E and the stilbene resveratrol as well as food preservatives such as sulfite, benzoate and sorbic acid and also colorants like curcumin exert significant suppressive effects on the T helper (h)1 immune activation cascade in freshly isolated human peripheral blood mononuclear cells. Obviously, antioxidant compounds interfere with central immunoregulatory pathways such as tryptophan breakdown via indoleamine 2,3-dioxygenase (IDO) and neopterin production by GTP-cyclohydrolase I (GCH). Results show an anti-inflammatory property of antioxidants which could shift the Th1-Th2-type immune balance towards Th2-type immunity that is of utmost importance in allergic responses. Additionally, food preservatives reduce the number of pathogens to which humans are exposed by their diet, so that in agreement with the hygiene hypothesis the likelihood of allergy might increase. This review article discusses the beneficial effects which antioxidants may have to counteract inflammatory diseases, but also their potential in the increase of allergy and asthma in the Western world and their involvement in the obesity epidemic.