In exposures to cold temperatures, cooling of body parts results in various cold injuries and hypothermia, which is the most serious condition. Cold injuries include non-freezing injuries like chilblain, immersion foot and trench foot or freezing injuries like frostnip and frostbite.

The extremities of human body (fingers, hands, feet and toes) are the most vulnerable to cooling because they have a surface area that is large in relation to their volume; which means they lose heat more rapidly and get cold faster than the torso. They are also frequently in contact with cold surfaces e.g., hands and fingers with tools and weapons and feet and toes with cold ground. Contact with cold surfaces, especially metals, results in a rapid reduction of finger or hand skin temperature. In snowy conditions hands may occasionally also be in touch with snow. Single melting of snow on the skin rapidly increases heat loss from the body, resulting in a decrease of up to 8^oC in the skin temperature.

Toes, fingers, ears and nose are at the greatest risk because these body areas do not have major muscles to produce heat. In addition, the body preserves heat by favoring the internal organs and thus reducing the flow of blood to the extremities under cold conditions.

Heat balance of the extremities is dependent on the general thermal status of the body, as determined by the body surface and core temperatures, as well as on local cold stress. But once the body is cooled beyond a certain temperature, the recovery of thermal balance may occur in delay. Feet and toes especially are slow to recover because blood flow does not return to the foot unless the whole body is sufficiently warm. Active heating of the extremities or the torso by an auxiliary heater is an effective method to prevent cooling of the extremities.