The phrase may be a common one, but it's not that easy to "freeze to death," explains LiveScience. In fact, it's a bit of a misnomer: Hypothermia will almost certainly get you before the body freezes. For the record, the body has two helpful reactions when the temperature drops: Blood moves from the skin and extremities to the body's core, and shivering begins.
Hypothermia sets in when the body's core temperature—normally 98.6 degrees—drops below 95. When it reaches 91 degrees, amnesia can occur; at 82 degrees, most people pass out, and at 70 degrees, death can occur. Lesser problems like frostbite are far more common. If the windchill is 15 below, it can happen fairly quickly. Thankfully, the body is pretty good at retaining heat—unless it's wet. That increases heat loss by 25 times.