What is the life-threatening allergic reaction known for causing circulatory collapse and shock?

Anaphylaxis is a severe and potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen. This reaction can lead to circulatory collapse and shock due to the massive release of histamines and other chemicals into the bloodstream, causing blood vessels to dilate and resulting in a drop in blood pressure. The rapid onset of symptoms can include difficulty breathing, swelling of the face and throat, a rapid or weak pulse, and skin reactions like hives or redness.

In contrast, an asthma attack primarily affects the airways, causing difficulty breathing but not typically leading to circulatory collapse. Allergic rhinitis, commonly known as hay fever, involves nasal symptoms and does not result in severe systemic effects. Severe allergy, while a vague term, does not specifically describe the critical nature of anaphylaxis and can refer to a range of reactions that may not reach the threshold of anaphylaxis. Therefore, anaphylaxis is the condition that specifically encompasses the risk of shock and circulatory failure, making it the correct choice in this context.