Guide to Heat Index's Health Impact on People

Heat index is the combination of temperature and humidity to determine how hot it feels to the body.  High humidity levels negatively impact the body's means for sweat to evaporate and thus interfere with the body's natural cooling mechanism.  That's why 90 degrees with high humidity feels worse than a dry 100 degree day.

USA Today made a chart showing negative impacts of heat index levels (hat tip: Daily Caller).

Image from the Daily Caller

For those who use the metric system here is a quick conversion guide:

80 Fahrenheit (F) equals 27 Celsius (C)
90F = 32C
100F = 38C
110F = 43C
120F = 49C
130F = 54C