What condition is characterized by severe allergic reactions?

Anaphylaxis is the correct answer because it specifically refers to a life-threatening allergic reaction that occurs rapidly after exposure to an allergen. This condition can lead to symptoms such as difficulty breathing, swelling of the throat, hives, a drop in blood pressure, and even loss of consciousness. It is a medical emergency that requires immediate treatment, typically with epinephrine, to reverse the severe physiological changes that occur.

Other conditions listed, while serious, are not characterized primarily by allergic reactions. Asthma is a chronic respiratory condition that can be triggered by allergies, but it is not exclusively an allergic reaction; it involves inflammation and constriction of the airways. Shock can refer to a state of inadequate blood flow to organs due to various causes, and cardiac arrest is the cessation of heart function. Neither shock nor cardiac arrest is specifically associated with allergic reactions. Thus, anaphylaxis stands out as the condition directly linked to severe allergic responses.