In the era of climate change and warming temperatures, the impact of extreme heat on people over the age of 65 is a serious public health issue because they are the most vulnerable to heat illness and death.

New research from Penn State University found that extreme heat can begin to stress the human body at much lower levels of heat and humidity than previously thought.

"Heat stress is what kills," said Dr. Larry Kenney, a Penn State professor of physiology and kinesiology who specializes in how the body regulates temperature, particularly for seniors.