There are two medical problems which can result from cold exposure. One is frostbite, which is the formation of ice crystals within living tissue, most often the nose, cheeks, chin, fingers, and toes. The first sign is numbness and redness, followed by the development of a waxy, white or yellow plaque. In severe cases, frostbite leads to hemorrhagic blisters, gangrene and loss of the body part. The other complication of cold exposure is hypothermia, which is an abnormally low body temperature caused by loss of heat. The chief symptoms are shivering, confusion, memory loss, drowsiness, exhaustion, fumbling hands, and slurred speech.
To prevent hypothermia and frostbite, keep all body surfaces covered, including the head and neck. Synthetic materials such as Gore-Tex and Thinsulate provide excellent insulation. Since the body loses heat faster when wet, stay dry at all times. Change inner garments promptly when they become moist. Keep active, but get enough rest. Consume plenty of food and water. Be especially sure not to have any alcohol. Caffeine and tobacco should also be avoided.
Observe companions closely. Watch out for the "Umbles" - stumbles, mumbles, fumbles, and grumbles - which are important signs of impending hypothermia. If someone appears to be developing hypothermia, he or she should be insulated from the ground, protected from the wind, stripped of wet clothing, covered with a vapor barrier such as a plastic bag (except for the nose and mouth), warmed with hot water bottles in the armpits and groin, and transported immediately to a warm environment and a medical facility. Warm fluids (but not coffee or tea) may be given if the person is alert enough to swallow. The very old and the very young are at greatest risk for hypothermia.
From "International Travel and Health" (WHO)
Environmental health risks
From the Centers for Disease Control (CDC)
From "Health Information for Overseas Travel" (U.K.)
Environmental hazards: heat, cold and altitude