Heat index warnings can save lives on dangerously hot days − if people understand what they mean

The sticky combination of heat and high humidity can be more than uncomfortable -- it can be deadly. Mario Tama/Getty Images

You’ve probably heard people say, “It’s not the heat, it’s the humidity.” There’s a lot of truth to that phrase, and it’s important to understand it as summer temperatures rise.

Humidity doesn’t just make you feel sticky and uncomfortable – it also creates extra dangerous conditions on hot days. Together, too much heat and humidity can make you sick. And in severe cases, it can cause your body to shut down.