The killer lurking in the shadows of the current heat wave may be hot nights.
Illinois state climatologist Jim Angel says people get fixated on how hot it gets, but he says the nighttime temperatures can be just as important.
For folks without air conditioning, a nighttime respite from the worst of the heat gives the body a vital chance to recover from the stresses of the day.
But while the current heat wave has recorded 12 all-time daily highs so far this month, it also has registered 98 all-time overnight highs.
That's according to the National Oceanic and Atmospheric Administration.
And that's just all-time highs.
More than 1,200 locations have tied or broken daytime records this month while 3,128 night time highs have been tied or broken.