system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it feel so good to scratch a mosquito bite?

It feels sooo good, but why?
gpt
When you have an itch (not bug bite), you get a little signal sent to your brain saying "remove something that's stuck here". You scratch to remove the offending material, and this causes minor pain that your body compensates for by flooding the site with pain blocking stuff, and the little signal is shut down. When you get a bug bite, the nerve in your skin still complains to the brain that something is stuck there, so you scratch and the area you scratched gets covered in anti-pain stuff, so you no longer feel any bug bite and you get good feelings partially because your body sez "All right! Problem is solved, everything is good now!" for the next 15 seconds and also because those pain-blocking chemicals also make you feel happy, and your brain registers that, basically, this little patch of skin is drunk for a few seconds. But it's more the satisfaction of removing an irritant.