Hypothermia (low body temperature) refers to both a medical condition and a symptom of cold exposure. It occurs when the body falls below a certain temperature and cannot warm itself. Normal body temperature is considered 98.6 degrees. Hypothermia is considered anything below 95 degrees. Left untreated, hypothermia can become a medical emergency.
The integumentary system (skin) helps to regulate body temperature by controlling heat loss. The body generates heat through cellular metabolism, which is a fancy way of saying that living—at least in a human—keeps us warm.
As long as our bodies can generate at least as much heat as we lose, we maintain our core temperature. If we lose more than we make, we suffer from hypothermia.