Which of the following indicates a severe allergic reaction requiring immediate medical attention?

Swelling of the face or throat is a critical indicator of a severe allergic reaction, known as anaphylaxis, which requires immediate medical attention. This swelling can lead to airway obstruction, making it difficult for the affected individual to breathe. The presence of swelling in these areas suggests that the body is experiencing a significant and systemic allergic response, which can rapidly progress from mild symptoms to life-threatening situations.

Itchy eyes, hives, and nasal congestion, while uncomfortable and potentially indicative of an allergic reaction, typically do not require the same level of urgency as facial or throat swelling. These symptoms may suggest a milder allergy that can often be managed without immediate intervention. However, when someone presents with swelling of the face or throat, it is crucial to respond quickly by calling emergency services to prevent potential respiratory distress or failure.