Hypothermia develops when the body temperature falls below what is needed for proper bodily functions. When a part of the body, such as an arm, hand, foot, or leg, has tissue damage from being exposed to cold weather or water, this is called frostbite. Hypothermia and frostbite are medical emergencies. Frostbite can lead to gangrene and loss of the affected body part. It is important to prevent hypothermia and frostbite by taking precautions when the weather is cold.