Having claimed the lives of AT hikers in the past, hypothermia is the most serious threat to hikers on the Appalachian Trail. It occurs when the body temperature cools down below 95 degrees, when body heat is lost more quickly than the body can replace it. Sometimes happening under situations one would not consider threatening, it can be extremely dangerous. For example, it can occur when someone is sweating, stops hiking and a slight breeze comes along, causing the body to cool rapidly. In addition, wet clothing and wind chill exacerbate heat loss, making the situation worse.
Prevention is the best treatment. Because people are more susceptible to hypothermia when exhausted, sick or lacking nourishment, don't get overly fatigued and eat frequently to maintain an acceptable metabolic rate. Also, camp early, maintain body heat (starting fire), huddle together, and wear appropriate clothing. Clothes made of synthetic (polypro) and wool fabrics are better than cotton, and an outer shell that is waterproof and wind-resistant will help as well.
Shivering uncontrollably, mental confusion, slowed speach, pale, blue lips, ears, fingers and toes...
Put on properly insulated dry clothing and get somewhere warm. Curl inside a sleeping bag, drink warm, slightly sweetened fluids. If in a group, huddle inside a sleeping bag with the victim, maintaining skin-to-skin contact, and encourage the victim to exercise.
Folks who loves the outdoors don't care if it's hot or cold, as long as they're outside. The wise ones heed these Forest Service winter hiking safety tips.