The basic principles are to stop heat loss and preserve the heat the person has, and provide body fuel to generate more heat. If a person is shivering, they can warm themselves at a rate of 2 degrees C per hour. Therefore put on additional layers of clothing, or replace wet clothes with dry. Get them moving to increase their activity, and make sure their surroundings are as warm and still as possible. Provide food, ideal initially as hot liquids.
Carbohydrates provide a rapid source of energy while fats can provide a prolonged source of fuel.
Add warmth with a fire or from body to body contact. There are some particular risks associated with outdoor sports. As body moisture is lost, the volume of the circulation is reduced, which can lead to dehydration and makes the body more susceptible to hypothermia and other cold injuries. For a list of other articles written exclusively for BBC Health visit our Features' Index page. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites.