The heat loss from the head derived from the high and low changes of temperature is as follows: when the temperature is at 15℃, one third of the total body heat is dissipated from the head; at 0℃, it is one half; and at minus 15℃, it is three fourths. This fully shows that the lower the temperature is, the more heat the human body dissipates from the head. So the key point to keep warm in winter is to keep the head warm.