Long-lasting contact urticaria from castor bean.

Type I (immediate) and type IV (delayed) allergic reactions to castor bean developed in a stockroom worker in a coffee roasting plant. The exceptionally strong contact urticarial patch rest reaction persisted for more than 48 hours and was therefore called "long-lasting contact urticaria." Light and electron microscopic observations indicated that eosinophils and mast cells were activated and participated in patch test reactions, which include both type I and type IV allergic reactions. Although patch testing is an absolute prerequisite for an accurate diagnosis of delayed allergy, it should be stressed that skin tests should not be performed with castor bean because of its toxicity and potential danger.