What are the signs of anaphylaxis?

Anaphylaxis is a severe, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen. The signs listed in the correct answer include swelling of the throat, which can obstruct the airway, making breathing difficult. Difficulty breathing is a critical symptom, as it indicates the respiratory system's involvement in the reaction. The presence of hives, which are raised, itchy welts on the skin, shows an immune response to an allergen, and a rapid heartbeat can occur due to drops in blood pressure and an increase in adrenaline during a severe reaction.

These symptoms highlight the urgent nature of anaphylaxis and the need for immediate medical intervention, often with the administration of epinephrine. Other choices contain symptoms that may suggest different conditions, but they do not encompass the hallmark signs of anaphylaxis, which specifically reflect a multi-system response to an allergen.