Hypothermia is a serious illness brought on by being in cold conditions.

Hypothermia is when the core of the body (the inside, including the heart) falls to a temperature of about 30 degrees (about 8 degrees below normal). The body begins to shut down long before this, as it tries to keep the heat inside to the vital places such as heart and brain. This is why fingers and toes get very cold and suffer frostbite: the body simply shuts off the supply of warm blood to these parts.

It can be very difficult to get people to recover from hypothermia. One way is to blow very hot air into their lungs.

Some people on outdoor winter or mountain activities get hypothermia if they do not have proper protection. People suffer hypothermia most quickly, however, if they fall into a cold sea. The cold water touches the skin, and heat leaves the body by conduction. So, for example, anyone falling into the North Atlantic Ocean in winter may have only four minutes to be rescued unless they are wearing special protective clothing.