"Insulin" allergy due to zinc.

An investigation of two unrelated patients who had local cutaneous hypersensitivity reactions after injection of any commercially available insulin preparation has shown that the cause of the allergy was zinc. Zinc-insulin and zinc sulphate induced transformation and proliferation of peripheral-blood lymphocytes from these patients; they also induced the production of a specific leucocyte inhibitory factor. Intradermal skin-tests for zinc were positive in both patients. Similar studies carried out in a patient whose cutaneous allergy to insulin was corrected by changing from mixed beef-pork to pure pork insulin were negative. Zinc-free insulin did not produce any allergy in the first patients. The number of patients in whom zinc (which is present in all commercially available insulin preparations) is a cause of "insulin" allergy is unknown. These patients may by identified by intradermal skin-tests. This previously unrecognised allergy should be considered in all patients whose insulin allergy does not respond to conventional therapy.