Heat kills more people than any other extreme weather event, and deadly heat waves are getting longer and hotter as the climate warms.

his summer, huge swaths of the US have already faced record-breaking heat waves.

Staying cool—and informed about the risks heat poses—is essential.

Thomas Clanton is a professor of applied physiology and kinesiology at the University of Florida and an expert in the effects of heat on the body. Here, he explains how to recognize heat illness and the long-term consequences of this kind of stress:

Q: What is heat illness?

It’s a really broad spectrum. At the lowest end is heat exhaustion, and on the more extreme end we have heatstroke. The difference is really the presence of neurological symptoms in heatstroke. Throughout the spectrum, mild to severe injury to liver, heart, kidney, and muscle can be present.

So, you can have heat exhaustion and you’re probably still thinking pretty well, but you know you’re hot. You try to get out of the heat and you’re functional. However, heatstroke victims can go unconscious, lose motor control, or become delirious, so their ability to respond is limited.

Clinically, a person would be diagnosed with heatstroke if they have a temperature above 40 degrees Centigrade (104 degrees Fahrenheit) and also exhibit central nervous system symptoms.

Read the full article about heatstroke by Eric Hamilton at Futurity.