But in northern climes, sporadic hot weather is less common and is far more taxing on the population than prolonged heat and humidity in areas where people are accustomed to it. Excessive heat can kill by taxing the human body beyond its abilities to cope with extremes. Blood vessels dilate so the blood can circulate more quickly, closer to the skin's surface. The excess heat is then vented from the skin into the air, but only if the air temperature is lower than the body temperature. The hypothalamus also calls millions of tiny sweat glands into action.
Excessive heat breaks down the body's natural cooling system.
When sweat is evaporated into the air, it provides additional cooling. But too much humidity in the atmosphere prevents sweat from evaporating. On an intensely hot and humid day, people will drip with perspiration, even as they stand idly at the bus stop or sit on a park bench. Stay Out of the Kitchen Extreme heat can undermine physical well being so slowly and subtly that the dangers are not apparent until people have succumbed to the effects. The body's response to overexposure to high temperature and high humidity could lead to a severe sunburn, which is not only painful but also reduces the skin's ability to release excess heat, making the body more susceptible to heat-related illness.