The role of allergens and pseudoallergens in urticaria.

Adverse reactions to food are a frequently discussed cause of urticaria. In acute urticaria 63% of patients suspect food as the eliciting factor; however, this cannot be confirmed in prospective studies. In adults the rate of type I allergic reactions is below 1%, although in children the percentage appears to be higher. Also in chronic urticaria type I allergic reactions play only a minor role as an eliciting factor. The same holds for the physical urticarias. The role of pseudoallergic reactions has not been investigated for all types of urticaria, but apparently they are not important in physical urticarias; however, in acute urticaria pseudoallergic reactions against NSAID are responsible for approximately 9% of cases, and in a subset of patients with chronic urticaria a diet low in pseudoallergens has been proven to be beneficial in several studies, with response rates observed in more than 55% of patients. Double-blind, placebo-controlled challenge tests have shown that artificial food additives are not only to blame, with the majority of reactions being traced back to naturally occuring pseudoallergens in food.