Which environmental factor most strongly limits evaporative cooling in humid environments?

• A. High ambient temperature
• B. Low wind speed
• C. High radiant heat
• D. Relative humidity is the primary limiter of evaporative cooling.

Answer: (D)

Evaporative cooling depends on a vapor pressure gradient between moisture on the skin and the surrounding air. When air is humid, it already contains a lot of water vapor, so the gradient is small and sweat evaporates more slowly. That directly limits how much cooling you can gain from evaporation. So, relative humidity is the factor that most strongly constrains evaporative cooling in humid environments. Higher temperature, radiant heat, or lower wind can affect overall heat balance, but they don’t set the maximum evaporation rate like humidity does, since evaporation slows primarily when the air cannot take up more moisture.