What is anaphylaxis? Anaphylaxis, also referred to as an anaphylactic reaction or anaphylactic shock, is a severe and sometimes life-threatening allergic reaction. While it is not common, the severity of the reaction and its rapid onset, usually within a few minutes of exposure to the allergen, require immediate medical care. Anaphylaxis is caused by your body’s severe immune reaction to an allergen, leading to the release of chemicals that cause swelling and other severe symptoms. These symptoms can lead to swelling of the tissues around the throat and face that are severe enough to cause breathing difficulty and a sudden drop in blood pressure. Almost any allergen can cause anaphylaxis, and allergens that lead to anaphylaxis vary from person to person. These allergens can include foods, such as nuts or shellfish, insect or spider stings or bites, or medications, such as aspirin or penicillin. Once your anaphylactic reaction has been treated, health care professionals can help to identify the allergen that caused your reaction by using a series of tests, such as skin exposure to small amounts of different allergens, or by reviewing dietary logs with you. Once the triggering allergen is identified, you can best prevent anaphylaxis by avoiding the allergen and carrying a portable epinephrine injection kit, if recommended, to treat any serious allergic reactions. Anaphylaxis is a severe and life-threatening condition. Seek immediate medical care (call 911) if you experience any of the symptoms of anaphylaxis, such as sudden swelling of the face, throat or lips; difficulty breathing; dizziness; hives or skin changes; and a fast heartbeat.