[jacquesm]

It's the combination of temperature, humidity, wind and other factors that poses health risks.

https://www.weather.gov/tsa/wbgt

https://en.wikipedia.org/wiki/Wet-bulb_temperature

This stuff can and does kill and if you're not aware of it then pay attention: this is one of the more direct consequences of climate change, it may well push zones that are currently marginally habitable right into inhabitable.