Introduction: Insulin allergy to human insulin preparations during the treatment of diabetes is suggested to occur at rates ranging from <1.0% to 2.4%. These reactions vary from mild localized reactions, which resolve with repeated exposure, to life-threatening anaphylaxis and death. The management of persistent insulin allergy in type 1 diabetes mellitus is particularly complicated because ongoing treatment with insulin is essential.

Case presentation: We present the case of a 12-year-old Caucasian girl with localized allergy to the insulin excipient metacresol, and the subsequent desensitization therapy using continuous subcutaneous insulin infusion with simultaneous intravenous insulin infusion.

Conclusions: This is the first documented case of allergy to the metacresol component of insulin in the pediatric type 1 diabetes literature. We describe an approach to diagnosis and management of metacresol allergy in type 1 diabetes.