Which heat loss mechanism involves latent heat loss through evaporation of surface moisture such as sweat?

• A. Evaporation
• B. Conduction
• C. Convection
• D. Radiation

Answer: (A)

Evaporation of sweat cools the body because it uses latent heat of vaporization. When liquid water on the skin turns into water vapor, energy must be absorbed to break intermolecular bonds, and that energy comes from the body's tissues. Since the temperature of the sweat itself doesn’t have to rise for this process to occur, it’s latent heat loss—heat is lost without a rise in the liquid’s temperature. Among the options, only evaporation involves this phase-change energy transfer. Conduction relies on direct contact of heat with a cooler surface, convection uses moving air to carry away heat (sensible heat), and radiation emits infrared energy without a phase change. Sweating and its evaporation are the body’s main way to dissipate excess heat when environmental or metabolic heat is high.