Anaphylaxis occurs when the immune system has an extreme reaction to an allergen, according to the American Academy of Allergy, Asthma and Immunology. The reaction affects many systems in the body, with symptoms related to breathing, circulation, the skin and the stomach.
The immune system's job is to protect the body from foreign substances that can harm the body, says Mayo Clinic. In some people, the immune system attacks things that don't cause the body harm, resulting in an allergic reaction. Anaphylaxis is an extreme form of this reaction.
Anaphylaxis happens suddenly, usually within minutes of exposure to the trigger, notes WebMD. The immune system springs into action immediately, causing several reactions in the body. Difficulty breathing is a common symptom of anayphylaxis, but the condition can also cause a drop in blood pressure, swelling, hives and loss of consciousness.
Many potential allergens are triggers for anaphylaxis, states Mayo Clinic. The most common causes are medications, insect stings and food allergens, such as nuts, shellfish or eggs. Many people with allergies to these items don't have a severe reaction. The severity of a past reaction doesn't always indicate the severity of a future reaction. A person who has a minor case of anaphylaxis one time may experience a more severe anaphylactic reaction with the next exposure to the allergen.