An insulin allergy is an allergic response to insulin medication. Insulin is a hormone normally produced by the pancreas to regulate glucose (blood sugar) levels. Insulin is sometimes taken in medication form because some people’s bodies do not produce it, cannot produce enough of it or cannot use it properly. All patients with type 1 diabetes and some people with type 2 diabetes, gestational diabetes and other forms of diabetes (e.g., maturity-onset diabetes of the young) require insulin to manage their glucose levels.

Methods of insulin administration include syringe injections, insulin pumps, insulin pens and jet injectors. In 2006 the U.S. Food and Drug Administration approved the first form of inhaled insulin, a powder that is delivered via an inhaler through the mouth to the lungs. Other methods are being developed, including skin patches, pills and insulin sprayed through the nose.

Some people have an allergic response to insulin medication, although this reaction occurs rarely. An allergic reaction occurs when the body mistakenly perceives the drug as a threat. As a result, the immune system steps up to protect the body from the perceived threat and produces a specific type of antibody to later recognize that allergen. These antibodies flow through the bloodstream and eventually attach themselves to mast cells, which contain a variety of chemicals, including histamines. The antibodies then wait for another encounter with the allergen.

This process of sensitizing a person to an allergen usually takes seven to 10 days. However, it does not produce any allergic symptoms. People do not become aware that this process has occurred until the next time they encounter that allergen. At that time, a chain of reactions including the release of histamine will occur, and allergy symptoms will appear.

The allergic reactions associated with the use of injectable insulin include:

• Local (only in the area where the insulin was injected)
• Anaphylaxis (affecting two or more body systems)

Inhaled insulin appears to produce a greater antibody response than injected insulin, according to recent research. Yet inhaled insulin was not found to increase allergic reactions or other medical complications such as hypoglycemia or lung dysfunction. Additional studies are under way to assess the long-term safety of inhaled insulin.

In the past, the most commonly used insulin was derived from the pancreases of cows and pigs. The insulin produced in cows and pigs is similar to the insulin produced in the human body. The only difference is in the sequence of a few of the amino acids that compose the insulin molecule. This small difference is enough to trigger an allergic reaction in some people. As a result, most people today use synthetic human insulin.

Synthetic human insulin is produced by genetic engineering. It is nearly identical to the insulin naturally produced in the body and it is less likely to cause an allergic response.  However, complications are also rare in patients who take animal-derived insulin.

Sometimes patients who suffer allergic reactions from an insulin injection are not allergic to the insulin molecule but are responding to the additives in the insulin. All forms of insulin medication have added ingredients, according to the American Diabetes Association. These additives are used to prevent the growth of bacteria and mold, to preserve the insulin and to maintain the balance of acids and bases. Intermediate-acting insulin and long-acting insulin also contain additives such as zinc and protamine, which cause the body to absorb the insulin at a slower rate.

The bacteria and impurities present in insulin can cause allergic responses. However, technological advances have improved the purity of insulin. Synthetic human insulin is especially pure because it is not combined with other proteins.

In some situations, the reaction is triggered by something other than the insulin. The substances found in insulin vials and syringes, including rubber or latex tops, can induce allergic reactions. Skin-cleansing agents can also cause a reaction.

Insulin allergies are more common in patients with a history of interrupted insulin therapy. The allergy usually appears within one to two weeks after the therapy is resumed.

Not all reactions to insulin are allergic reactions. Sometimes reactions are simply side effects of the medication that do not involve the formation of antibodies.