Record heat has claimed 23 lives and the weather shows no signs of letting up.

But what is it that causes people to succumb to high temperatures?

The ability to sweat is what keeps the body cool.
Once high humidity becomes part of the equation, sweating is no longer as effective.

Extreme temperatures make it difficult for a heat-stressed individual to be aware of the danger since the brain and central nervous system are particularly sensitive to high internal temperatures.

Hot weather alone is not dangerous, said Chris Minson, an environmental physiologist at the University of Oregon, Eugene. Instead, it’s a combination of hot temperatures, high humidity, and often preexisting health conditions that can push a person’s core body temperature to reach the danger zone of 104 F. At that point, the nervous system goes haywire, the heart experiences excessive stress, and organ systems begin to fail.