What is the primary mechanism by which sweating cools the body?

• A. Conduction
• B. Evaporative cooling
• C. Convection
• D. Radiation

Answer: (B)

The main concept is evaporative cooling. When sweat reaches the skin, it must evaporate to become vapor. That phase change requires a large amount of energy—the latent heat of vaporization—taken from the skin and nearby tissues, which lowers skin temperature and overall body heat. This makes sweating the primary way the body sheds heat during hot or strenuous conditions, especially when air movement or moderate humidity allows rapid evaporation.

In contrast, conduction, convection, and radiation transfer heat without relying on changing the water’s phase. They can contribute to heat loss or gain but aren’t driven by the energy sink created by turning liquid water into vapor. Evaporation remains the most effective cooling process under typical environmental conditions because it can remove heat even when ambient temperatures are high, though high humidity can slow evaporation and reduce cooling efficiency. For intuition, each gram of sweat that evaporates absorbs about 2 kJ of heat, a substantial cooling effect.