system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if my blood's temperature is 98.6, why does 80 degrees feel hot and 60 degrees feel cold?
gpt
Our bodies produce heat to maintain that temperature (realistically, it's normally anywhere from 97-99 degrees), but the body also loses heat to the outside air, so it produces more heat than "just barely enough to maintain 98 degrees." When the temperature outside goes up, you're not losing as much heat as normal, so your skin expands for more surface area, sweats to induce evaporation and your blood vessels expand in your extremities, all of which allow your body to lose heat more quickly to maintain a normal internal temperature. When it gets cold, sweating stops, your skin contracts and your blood vessels contract in your extremities to slow down the loss of heat.

[Edit]: Humidity plays a big part in this, too, because sweating is the most efficient method of getting rid of heat. 80 degrees with low humidity can be pretty comfortable for most people, because rapid evaporation of your sweat keeps your body temperature well-regulated. When the humidity is high, though, evaporation of sweat occurs more slowly, so you feel hotter and sluggish, so as to not increase the amount of heat you're producing internally.