What is the medical term for an exaggerated immune response to a substance?

The medical term for an exaggerated immune response to a substance is allergy. Allergies occur when the immune system reacts overly sensitively to substances that are generally harmless to most people, known as allergens. Common allergens include pollen, animal dander, certain foods, and medications. Upon exposure to these allergens, the immune system produces specific antibodies called immunoglobulin E (IgE), leading to the release of chemicals like histamine, which causes allergic symptoms such as itching, swelling, and difficulty breathing.

Other choices represent different medical concepts. An infection involves the invasion of the body by pathogens such as bacteria, viruses, or fungi, leading to disease and requiring a different immune response. Inflammation is a natural response of the body to injury or infection and includes swelling, redness, and heat as the body's way of healing. Autoimmunity refers to a condition where the immune system mistakenly attacks the body's own cells, believing them to be foreign, which is distinct from an exaggerated response to an external substance.