Additive-induced urticaria: experience with monosodium glutamate (MSG).

In patients with chronic urticaria, the incidence of reactions to any additives, including monosodium glutamate (MSG), is unknown. Although many studies have investigated the association of additives and urticaria, most have been poorly designed. This study sought to determine the prevalence of reactions to additives, including MSG, in patients with chronic urticaria using a rigorous protocol. We studied 65 subjects (44 women, 21 men; ages 14-67). All had urticaria for >6 wk without discernible etiology. Subjects with active urticaria were studied while they were taking the lowest effective dose of antihistamine. Screening challenges to the 11 additives most commonly associated with exacerbations of chronic idiopathic urticaria were performed in a single-blind fashion. The dose of MSG given was 2500 mg. Skin scores were obtained to determine a positive reaction in an objective manner. Subjects with a positive screening challenge were rechallenged (at least 2 wk later) with a double-blind, placebo-controlled protocol as in-patients in our General Clinical Research Center. Two subjects had positive single-blind, placebo-controlled challenges, but neither had a positive double-blind, placebo-controlled challenge. We conclude, with 95% confidence, that MSG is an unusual (<3% at most) exacerbant of chronic idiopathic urticaria.