If the temperature of the body is higher than the temperature of the surrounding objects, a greater quantity of heat is radiated away from the body than is radiated to the body. The proximity of these objects will determine the overall rate of conduction. Convection is the transfer of heat from the body in liquids or gases in which molecules are free to move. Respiration, which contributes to the regulation of body temperature, is a type of convection. When water on the surface of the body evaporates, heat is lost.
Evaporation is the most common and usually the most easily explained form of heat loss.
When the temperature of the air and nearby objects exceeds skin temperature, the body actually gains heat. This gain may be dangerous to the aviator. When the temperature increases to about 82 to 84 degrees Fahrenheit, sweat production increases abruptly to offset the loss of body cooling through radiation, convection, and conduction. By the time the temperature reaches 95 degrees Fahrenheit, sweat evaporation accounts for nearly all heat loss. Many factors affect the evaporation process.