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Anaphylactic
reactions (anaphylaxis) are sudden, widespread, potentially severe
and life-threatening allergic reactions.
Anaphylactic reactions are most commonly caused by drugs (such as penicillin), insect stings, certain foods, and allergy injections (allergen immunotherapy). But they can be caused by any allergen. Like other allergic reactions, an anaphylactic reaction does not usually occur after the first exposure to an allergen but may occur after a subsequent exposure. However, many people do not recall a first exposure. Any allergen that causes an anaphylactic reaction in a person is likely to cause that reaction with subsequent exposures, unless measures are taken to prevent it.
Symptoms
Anaphylactic reactions begin within 1 to 15 minutes of exposure to the allergen. Rarely, reactions begin after 1 hour. The heart beats quickly. The person may feel uneasy and become agitated. Blood pressure may fall, causing fainting. Other symptoms include tingling (pins-and-needles) sensations, itchy and flushed skin, throbbing in the ears, coughing, sneezing, hives, and swelling (angioedema). Breathing may become difficult and wheezing may occur because the windpipe (upper airway) constricts or becomes swollen.
An anaphylactic reaction may progress so rapidly that it leads to collapse, cessation of breathing, seizures, and loss of consciousness within 1 to 2 minutes. The reaction may be fatal unless emergency treatment is given immediately.
Prevention and Treatment
People who are allergic to unavoidable allergens (such as insect stings) may benefit from long-term allergen immunotherapy (see Allergic Reactions: Allergen Immunotherapy).
If an anaphylactic reaction occurs, an epinephrine injection should be given immediately. People who have these reactions should always carry a self-injecting syringe of epinephrine and antihistamine tablets for prompt treatment. Usually, this treatment stops the reaction. Nonetheless, after a severe allergic reaction, such people should go to the hospital emergency department, where they can be closely monitored and treatment can be adjusted as needed.
Last full review/revision February 2003
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