The sense of temperature describes the ability to sense warm and cold stimuli and react accordingly. In humans, the sense of temperature is limited to the skin and certain mucous membranes, namely to warm and cold spots on these membranes. The skin contains sensors, which react to changes in the surrounding temperature. On the skin, there are different sensors that can only sense one type of sensation, either cold or warm. On the face and the extremities, there are up to ten cold spots and one warm spot per square centimeter. The physiological zero point is defined as the skin temperature, at which there is no temperature sensation.
Depending on the part of the body the zero point lies between 28 and 33° C (82.4 and 91.4° F). In order for the metabolic processes in the human body to function properly, the body temperature has to be kept at 37° (98.6° F). Below lower limit, death. 25° C (77° F) moderate hypothermia. 33° C (91.4° F) mild hypothermia. 35° C (95° F) normal temperature (afebrile). 36–37° C (96.8–98.6° F) elevated temperature (subfebrile). 37–38° C (98.6–100.4° F) mild fever (febrile). 38–39° C (100.4–102.2° F) high fever. 39–40.5° C (102.2–104.9° F) very high fever (hyperpyrexia). 41° C (105.8° F) circulatory failure. 42° C (107.6° F) over 42.6° C death through denaturation of proteins and enzymes. If the temperature rises above the desired value, the blood flow to skin and extremities is increased in order to increase heat exchange through the body surface. The condensation of water, which is excreted by perspiratory glands, increases the cooling effect. The human body has 2-4 million perspiratory glands. Shivering is a natural reaction to a low surrounding temperature. Using this protective reflex, the body tries to prevent an extreme decline in body temperature. The blood vessels in the skin contract, the blood flow to body extremities which are not indispensable to life, like fingers, toes, ears, etc., is limited, the fine body hairs are raised (goose bumps), and the muscles start trembling.