Why are humans most comfortable at room temperature (65-70 degrees), and not at 98.6 degrees?
You need a heat sink to dump your body’s waste heat into. How effectively your body can radiate this excess thermal energy (produced by your metabolism) depends on the temperature of the surrounding environment, it’s conductivity, it’s humidity, etc. 70 degrees with middling humidity makes it easy to dump the waste heat without discomfort. As temperature (or humidity) rises, it gets harder.
Qadgop did a good job, but just for reference, here’s what Cecil says.