Anaphylaxis is a severe, rapid allergic reaction that can lead to potentially fatal anaphylactic shock. This occurs when blood pressure drops suddenly, making it hard for the heart to get oxygen, and airways constrict, making breathing difficult.

Triggers include allergies to medications, certain foods (like peanuts, tree nuts, shellfish, eggs, and milk), insect stings, and latex. Environmental allergens like pollen and animals typically do not cause anaphylaxis.

Anaphylaxis is a medical emergency requiring immediate treatment with an epinephrine auto-injector (EpiPen) and observation by a trained physician.