Why is eu-de-cologne applied to the forehead of a person suffering from high fever?

We have temperature signals in the peripheral areas of our body. These areas are found especially in the skin and certain deep body tissues. These centres contribute very significantly to body temperature regulation. They do this by altering the set point of the hypothalamic temperature control centres. Set point is the particular temperature at which sweating begins. The average normal temperature i.e., the hypothalamic temperature of our body is considered to be between 36.7 to 37 degrees centigrade (98 degrees Fahrenheit to 98.6 degrees Fahrenheit). It is also called as core temperature. Here the skin temperature will be 33 degrees centigrade.

When the skin temperature rises above this, due to warm weather and other reasons, immediately sweating begins. So when the skin temperature is very high sweating begins at a lower hypothalamic temperature i.e., is at the core temperature itself.

On the other hand during high fever both the skin temperature and the hypothalamic temperature begin to rise. The skin temperature will be above 33 degrees centigrade and the hypothalamic temperature will be above 37 degrees centigrade. Since the core temperature is above normal sweating will not occur and so there will not be loss of body head. But when the skin temperature is reduced to 29 degrees centigrade we can induce sweating even at much high hypothalamic temperature. This can be done artificially by spreading wet cloth dipped in ice cold water over the body, especially in the forehead or applying eu-de-cologne, which is a cooling agent.

Source : The Hindu