An insulin allergy is an allergic response to an insulin medication.  Insulin is a hormone normally produced by the pancreas that is taken via injection or other means by some people with diabetes. People whose bodies do not produce insulin or cannot use it properly may be prescribed insulin to regulate their glucose (blood sugar) levels.

Some people have an allergic response to insulin medication, although it occurs rarely.

An allergy occurs when the immune system identifies a harmless substance as being dangerous and produces antibodies to fight the substance. For some people with insulin allergies, the allergy goes undetected until they suffer an allergic reaction.

Insulin allergies occur because injectable insulin is not exactly the same as naturally produced human insulin. Insulin medication in the United States is almost exclusively a form that is genetically engineered to resemble natural human insulin.  The chemical makeup of these human insulins is often modified slightly to change the duration of the insulin action. Rarely insulin from animal sources is used to treat diabetes. Allergic reactions are reactions to these differences, as well as the additives, bacteria and impurities that are present in synthetic human and animal-derived insulin. Insulin allergies are more common with insulin made from animals than with synthetic human insulin.

Allergic reactions associated with the use of insulin can be local (appearing around the injection site) or can affect two or more body systems (anaphylaxis). A local allergic reaction may cause itching, redness or swelling at the injection site. Anaphylaxis may cause breathing difficulty, rash and a drop in blood pressure. Without immediate emergency treatment, anaphylaxis can quickly progress to anaphylactic shock and become deadly.

If the patient must keep taking insulin (e.g., anyone with type 1 diabetes and some people with type 2 diabetes and other forms of diabetes), a physician may treat an insulin allergy with desensitization. Desensitization is the process of reducing or eliminating a patient’s sensitivity to an allergen.