What severe allergic reaction can lead to difficulty breathing and potentially death if untreated?

Anaphylaxis is the correct response because it is a rapid and severe allergic reaction that can occur in response to allergens such as certain foods, medications, or insect stings. This reaction leads to a cascade of symptoms, including swelling of the throat, difficulty breathing, a sudden drop in blood pressure, and potential loss of consciousness. If not treated immediately, typically with an injection of epinephrine, anaphylaxis can progress quickly to respiratory failure or even death.

Other options, while they involve allergies, do not present the same level of immediate life-threatening risk. Asthma, for instance, can cause breathing difficulties, but it is generally a chronic condition that can be managed with medications and does not represent an instant, severe allergic response. Allergic rhinitis, commonly known as hay fever, primarily affects the nasal passages and does not lead to systemic reactions like anaphylaxis. Urticaria, or hives, often results in skin reactions but does not typically affect breathing directly. Thus, anaphylaxis stands out as the immediate and life-threatening allergic reaction in this context.