Hypothermia, a potentially fatal condition, occurs when body temperature falls below 95°F (35°C). Although it is an obvious danger for people living in cold climates, many cases have occurred when the air temperature is well above freezing. Elderly people, for instance, have succumbed to hypothermia after prolonged exposure to indoor air temperatures of 50-65°F (10-18.3°C).

Measured orally, a healthy person's body temperature can fluctuate between 97°F (36.1°C) and 100°F (37.8°C). Survival depends on maintaining temperature stability within this range by balancing the heat produced by metabolism with the heat lost to the environment through (for the most part) the skin and lungs. When environmental or other changes cause heat loss to outpace heat production, the brain triggers physiological and behavioral responses to restore the balance. Shivering, for example, aids heat production by accelerating metabolism. But if the cold...