What are the signs of a severe allergic reaction?

The signs of a severe allergic reaction, also known as anaphylaxis, include difficulty breathing, swelling of the face or throat, and a rapid heart rate. This severe response occurs when the body's immune system overreacts to an allergen, leading to significant physiological changes. Difficulty breathing is often caused by swelling in the airways, which can obstruct airflow and result in wheezing or stridor. Swelling of the face or throat is indicative of angioedema, which can further compromise the airway. A rapid heart rate is a compensatory mechanism due to the body's stress response to the allergic reaction, as the cardiovascular system attempts to maintain adequate blood flow and oxygenation to vital organs. Recognizing these critical signs is essential for prompt intervention, as anaphylaxis can be life-threatening and requires immediate treatment, typically with epinephrine and emergency medical services.

Other signs such as itchy skin and minor swelling, headaches, migraines, or localized redness and rash typically reflect less severe allergic responses or other conditions and do not signify the acute and life-threatening nature of anaphylaxis. Hence, they are not included among the signs of a severe allergic reaction.