When a person's body has an allergic or bad reaction to taking insulin made from pork or beef or from bacteria, or because the insulin is not exactly the same as human insulin or because it has impurities. The allergy can be of two forms. Sometimes an area of skin becomes red and itchy around the place where the insulin is injected. This is called a local allergy. In another form, a person's whole body can have a bad reaction. This is called a systemic allergy. The person can have hives or red patches all over the body or may feel changes in the heart rate and in the rate of breathing. A doctor may treat this allergy by prescribing purified insulins or by desensitization. See also: desensitization.