Which of the following is a sign of anaphylaxis?

Swelling of the mouth or throat is a hallmark sign of anaphylaxis, which is a severe and potentially life-threatening allergic reaction. This swelling can lead to airway obstruction, making it difficult for the person to breathe. Recognizing this symptom is critical for lifeguards and emergency responders because immediate action, such as administering epinephrine, may be necessary to prevent a potentially fatal outcome.

Other signs associated with anaphylaxis include symptoms such as hives, increased heart rate, and excessive sweating, but swelling of the mouth or throat represents a direct threat to the airway and is particularly urgent. While excessive sweating and increased heart rate can occur during anaphylactic reactions, they are not the most definitive indicators when compared to the danger posed by airway swelling. Hives, another common symptom of allergies, can occur in anaphylaxis, but the presence of throat or mouth swelling is the most critical sign that warrants immediate medical intervention.