Many different additives are added to the food that we consume, and the number of additives is estimated to range from 2,000 to 20,000. These substances include preservatives, stabilizers, conditioners, thickeners, colorings, flavorings, sweeteners, and antioxidants. Despite the multitude of additives known, only a surprisingly small proportion of them has been associated with hypersensitivity reactions. A number of investigators have suggested that a significant proportion of patients with chronic urticaria, angioedema, atopic dermatitis, and asthma have symptoms related to the ingestion of food additives. However, the incidence and mechanisms of reactions to additives in patients with chronic urticaria, angioedema, and atopic dermatitis remain unknown. Monosodium glutamate(MSG) produces the flavor-enhancing properties of seaweed, the traditional component of Japanese and Chinese cooking. A few studies on MSG have reported an association between MSG and atopic dermatitis, but the exact nature of the relationship remains unknown. Dyes approved under the Food Dye and Coloring Act are coal tar derivatives, the best known of which is tartrazine(FD& C yellow no. 5). The group of azo dyes includes ponceau(FD& C red no. 4) and sunset yellow FD& C yellow no. 6). Amaranth(FD& C red no. 5) was banned from use in US in 1975 due to the claims related to carcinogenicity. Most of them were reported to be associated with an aggravation of atopic dermatitis. Parabens are aliphatic esters of parahydroxybenzoic acid. Sodium benzoate is a closely related substance usually reported to cross-react with these compounds. These agents, which are widely used as preservatives in both foods and drugs, are well recognized as the cause of severe contact dermatitis. Additives can serve as haptens to create a response mediated by IgE. Only a few reports have suggested IgE-mediated reactions, notably to sulfites and parabens. Instead, the overwhelming majority of these reactions are not of the immediate hypersensitivity type. Many cases of additive-provoked urticaria or dermatitis occur as late as 24 hours after the challenge, arguing against an IgE-mediated mechanism.
