Corn sweat is an agricultural phenomenon that makes humidity during a heat wave even worse, especially in states like Illinois where it's a major cash crop.

"Corn gets the name corn sweats because corn puts out a lot of water vapor," Glisan said. "That's where we get these exceedingly high dew points and this oppressive heat, not because of corn, but corn and vegetation in general helps add a few points to the dew point on it."