As sweat evaporates from our skin, it cools us off. Our personal cooling system can fail, though, if we overexert ourselves on hot and humid days. This can result in heat exhaustion or a heat stroke, which is life-threatening.
Heat exhaustion takes time to develop.
Fluids and salt are vital for health. They are lost as children and adults sweat a lot during exercise or other strenuous activities. It is very important to drink lots of non-alcoholic liquids before, during and after exercise in hot weather. As strange as it seems, people suffering from heat exhaustion have low, normal or only slightly elevated body temperatures. When the body's cooling system fails, the body's temperature rises fast.