Risk Factors for Heat Exhaustion
Heat exhaustion is strongly related to the heat index, which is a measurement of how hot you feel when the effects of relative humidity and air temperature are combined. A relative humidity of 60% or more hampers sweat evaporation, which hinders your body’s ability to cool itself.
The risk of heat-related illness dramatically increases when the heat index climbs to 90 degrees or more. So it’s important — especially during heat waves — to pay attention to the reported heat index, and also to remember that the heat index is even higher when you are standing in full sunshine.