Which environmental factor most increases the risk of heat-related illness in hot weather with high humidity?

• A. high humidity
• B. low humidity
• C. strong wind
• D. rain

Answer: (A)

High humidity makes heat illness more likely because sweating, your main cooling mechanism, evaporates poorly when the air is already saturated with moisture. When sweat doesn’t evaporate efficiently, your body has a harder time shedding heat, so core temperature rises faster in hot conditions. This is why the heat index—how hot it feels combining temperature and humidity—is a key risk indicator in hot, humid weather.

Low humidity actually helps cooling because sweat can evaporate more readily. Strong wind aids cooling by removing heat from the skin and increasing evaporation, reducing risk. Rain can offer some cooling but isn’t the primary factor driving risk in hot, humid conditions. So the environmental factor that most increases risk is high humidity.