Many people think of hypothermia as strictly an extreme cold weather problem. In fact, hypothermia occurs when the body’s core temperature reaches 95 °F or less. That can occur even when temperatures are above freezing. There are two types of hypothermia. Acute hypothermia occurs when the body temperature drops rapidly, as might happen with a plunge into icy waters. Chronic hypothermia occurs over longer periods of time, such as when a hiker works up a sweat during cold weather or is out in damp, cold conditions. Acute hypothermia can be the most dangerous since it can occur in seconds. Chronic hypothermia is most easily avoided. Most heat is lost through the head, so wearing a hat can be a simple preventive measure. Another is to wear fabrics which can wick away moisture. These include wool or synthetic fabrics designed specifically for rapid drying.
Mary Knapp, Weather Data Library