Sulfite-induced urticaria.

Metabisulfite sensitivity is being described with growing frequency. Sulfites are used in food, drinks, and drugs. Adverse reactions to apparently nontoxic doses have been described. Exposure of sensitive persons to sulfites has produced asthma, and occasionally other adverse reactions in nonasthmatic patients. We present a case of urticaria induced by metabisulfites. During the previous 2 years the patient had suffered episodes of urticaria and angioedema limited to the face, neck, upper thorax, and dysphonia without asthma after the ingestion of food and drinks containing sulfites. Oral challenge with 25 mg of potassium metabisulfite elicited urticaria on the face and neck, nasal itching, rhinorrhea, and dysphonia. Prick and intradermal tests were negative. Two further challenges with the same doses were also positive. One of these was controlled with placebo, 30 minutes after oral administration of 400 mg sodium cromolyn; the second was carried out 90 minutes after oral administration of 5000 micrograms cyanocobalamin. We have been unable to identify a pathogenic mechanism.