specialize in problems relating to immunity—how the human body reacts to foreign substances, resistance to disease and other threatening substances. They evaluate, diagnose, and help patients manage disorders including seasonal allergies, asthma, hay fever, eczema, food and drug reactions, insect stings and hives. They also treat acquired and congenital conditions related to the immune system. These specialists have had special training to identify the factors that trigger allergic diseases, and help patients prevent or treat these conditions.