A significant increase in the incidence of allergy and asthma has been observed during the past decades. The background of this phenomenon has not been well explained, but changes in lifestyle and habits are heavily discussed as contributing factors. Among these is a too clean environment, which may predispose individuals to increased sensitivity to allergic responses. Also the increase in dietary supplements including preservatives and colorants may contribute to this. In vitro, we and others have shown in freshly isolated human peripheral blood mononuclear cells that antioxidant compounds like vitamins C and E as well as food preservatives and colorants exert significant suppressive effects on the Th1 immune activation cascade. The effects observed may be based on the interaction of antioxidant compounds with proinflammatory cascades involving important signal transduction elements such as nuclear factor-ĸB. Although only obtained in vitro, these results show an anti-inflammatory property of compounds which could shift the Th1-Th2-type immune balance towards Th2-type immunity. This review article discusses the potential role of increased use of antioxidant food supplements as well as preservatives and colorants in the increase in allergy and asthma in the Western world.