Alright so for some reason, despite me being literally directly next to a campfire, the temperature of the charactor still goes down. Here is proof of the issue: http://prntscr.com/j5cczk

Need a bit more info...What season is it? What version are you using (Since temperature values were balanced a lot more recently)?

Anyway, I'm just gonna close this because I know for a fact that they do work. A campfire by itself isn't going to save you if you're outside in the middle of winter though.

Im using the most recent version (i believe) and It's either early or mid spring.
Im also underground (though, not deep underground)

Also, I'm in a Taiga biome.

A couple side notes, the bug fixed itself after restarting the game and it was night-time when it happened.