Although it rarely happens, allergies can kill. Some people have such an extreme sensitivity to a particular substance that the allergen can trigger an episode known as an anaphylactic shock. A sudden, potentially fatal reaction, anaphylactic shock lowers blood pressure, swells the tongue or throat, and constricts the airways of the lungs, making it difficult to breathe.
Such a reaction requires immediate medical attention. Anaphylactic shock is most often triggered by a food or drug, but it can also result from an insect sting or even, rarely, from immunotherapy for an allergy. People with a history of severe allergic reactions should always carry a pre-loaded syringe of epinephrine (a synthetically produced form of the hormone adrenaline), which can be administered in an emergency.