An allergic reaction occurs when the body's immune system mistakenly identifies a harmless substance, known as an allergen, as a threat. Common allergens include pollen, pet dander, certain foods, and insect stings. When exposed to an allergen, the immune system releases chemicals like histamine, leading to symptoms such as sneezing, itching, hives, or swelling. In more severe cases, an allergic reaction can result in anaphylaxis, a life-threatening condition that requires immediate medical attention. Symptoms of anaphylaxis may include difficulty breathing, rapid heartbeat, and a drop in blood pressure. It is essential for individuals with known allergies to avoid triggers and carry emergency medication, such as an epinephrine auto-injector.