Well, when you think about... normal human body temp is 100° F, give or take. I tend to run a degree lower - others a degree higher. That's normal.
I studied the US Navy Dive Tables, back when I was into SCUBA diving. The 'perfect' ambient temperatures (if you will) for humans is 88° F in air, and 92° F in water. Without turning this into a 'white paper', they determined that by how long divers could maintain their body temp (98.6° F) sitting naked for 24 hours, at rest, in air and in water. At 88° F in air, and 92° F in water, one can maintain their normal body temperature indefinitely.
My take away, having lived in Arizona my whole life is, 105° F is the breaking point. The closer one gets to 105° in air, the more uncomfortable one will become. However, 105° F and above, given enough time, WILL kill you - guaranteed.