Unlike warmblooded animals that have a layer of hair or blubber to keep them warm, you need an extra layer of clothing to keep you warm when it's cold outside. Without that extra layer of clothing, more heat escapes from your body than your body can produce. If too much heat escapes, the result is hypothermia. Exposure to cold water and certain medical conditions also can cause hypothermia.

Hypothermia occurs when your body's control mechanisms fail to maintain a normal body temperature. Your normal core body temperature is usually right around 36.8 C. An internal body temperature of 36 C or lower signals hypothermia.

• 34 - 36 C (mild hypothermia)
• 30 - 33.9 C (moderate hypothermia)
• < 30 C (severe hypothermia)

Signs and symptoms that may develop include gradual loss of mental and physical abilities. Severe hypothermia can lead to death. Hypothermia isn't a serious risk. Those at greatest risk are older adults, children, people who are mentally ill or have Alzheimer's disease and lose their judgment about when to seek shelter, and people who are intoxicated, homeless or caught in cold weather because their vehicle has broken down.

Wearing protective clothing and taking other precautions can ensure that your body temperature doesn't drop to deadly levels. Paying attention to what may be early signs and symptoms of hypothermia also is important.

• Alzheimer's disease
• Cold