Heat exchange with the environment involves 4 basic processes—
Warm objects lose heat energy as infrared radiation. When we feel the sun's heat, we are experiencing radiant heat. Your body loses heat the same way. More than half of the heat you lose occurs by radiation, (primarily infrared).
Conduction is the direct transfer of energy through physical contact.
When you sit on a cold plastic chair in an air-conditioned room, you are immediately aware of this process. Conduction is generally not an effective mechanism of gaining or losing heat, except in a manner opposite of that desired, (i.e., trauma victims lying a ground cooler than 98F (37C) rapidly cool, partly through conduction.)
Convection is the result of conductive heat loss to the air that overlies the surface of an object.
Warm air rises because it is lighter than cool air. As your body conducts heat to the air next to your skin, that air warms and rises, moving away from your skin surface. Cooler air replaces it, and as this air in turn warms, the pattern repeats.
When water evaporates, it changes from a liquid to a vapor. This process absorbs energy—roughly 580 calories (0.58 Cal) per gram of water evaporated— and, thus, cools any surface on which it occurs.
The rate of evaporation and heat loss occurring at your skin is highly variable. Each hour, 20-25 ml of water crosses epithelia and evaporates from the alveolar surfaces of the lungs and the surface of the skin. This insensible perspiration remains relatively constant; it accounts for roughly one-fifth of the average heat loss from a body at rest. The sweat glands responsible for sensible perspiration have a tremendous scope of activity, ranging from virtual inactivity to secretory rates of 2-4 liters (or 2-4 kg) per hour. This is equivalent to an entire day's resting water loss in under an hour.