Hypothermia is generally defined as which condition?

Hypothermia is characterized by a significant drop in body temperature below the normal range, which typically is around 98.6°F (37°C). When the body temperature falls below approximately 95°F (35°C), it can have serious physiological impacts, impairing the body's ability to function properly and leading to various health challenges. This condition can result from prolonged exposure to cold environments or immersion in cold water, where the body loses heat more rapidly than it can produce it.

The other concepts presented do not define hypothermia accurately. The ability to maintain thermal regulation refers to how the body controls its temperature under varying conditions, while a decrease in blood circulation is more related to vascular function than to temperature regulation itself. Lastly, a severe allergic reaction to cold, often referred to as cold urticaria, does not define hypothermia but rather describes an adverse immune response triggered by cold exposure. Thus, the correct answer identifies hypothermia specifically as a condition where the body temperature falls below the normal biological threshold.