Subnormal temperature of the body.
Example:
By the time rescuers were able to pull the skater from the pond's icy waters, hypothermia had reached a life-threatening stage.
Hypothermia may constitute a grave medical emergency. Typical causes include submersion in icy water and prolonged exposure to cold. Hypothermia begins to be a concern when body temperature dips below 90 degrees Fahrenheit. Below 90 degrees Fahrenheit, the point at which the normal reaction of shivering ceases, emergency treatment is called for.