Similar term(s): hypersensitivity, allergen, allergic reaction, allergic disease, allergic disorder.
Allergies are inappropriate or exaggerated reactions of the immune system to
substances that, in the majority of people, cause no symptoms.
Symptoms of the allergic diseases may be caused by exposure of the skin to a
chemical, of the respiratory system to particles of dust or pollen (or other
substances), or of the stomach and intestines to a particular food.