What term describes a severe and often fatal allergic reaction to a foreign substance?

The term that describes a severe and often fatal allergic reaction to a foreign substance is "anaphylactic shock." Anaphylactic shock is a rapid and extreme immune response that occurs when an individual encounters a specific allergen, such as certain foods, medications, or insect stings. This reaction can lead to symptoms such as difficulty breathing, swelling of the throat, a sudden drop in blood pressure, and loss of consciousness. If not treated promptly with epinephrine and emergency medical intervention, it can result in death.

The other options refer to different types of allergic reactions or conditions. Asthmatic reactions are specific to asthma, where bronchial tubes become inflamed and narrowed, causing breathing difficulties, but they are not classified as anaphylactic shock. Hypersensitivity reactions encompass a broad range of allergic responses, including anaphylaxis, but they do not specifically denote the life-threatening nature of anaphylactic shock. Allergic rhinitis is a condition characterized by nasal inflammation due to allergens, leading to symptoms like sneezing and runny nose, which are generally less severe than anaphylaxis. Thus, anaphylactic shock is the precise term that captures the severity and urgency of a life-threatening allergic reaction.