Severe allergic reactions, also known as anaphylaxis, occur when the immune system overreacts to a substance, such as pollen, food, or insect stings. Symptoms can include difficulty breathing, swelling of the throat, rapid heartbeat, and a rash. These reactions can happen quickly and may be life-threatening if not treated promptly. Treatment for severe allergic reactions typically involves the use of epinephrine, which can help reverse symptoms. It is important for individuals with known allergies to carry an epinephrine auto-injector and seek immediate medical attention if they experience signs of anaphylaxis.