system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do humans like to kiss each other?
gpt
It releases hormones that feel good, such as oxytocin. 

Why does it release hormones like that? Because a kiss is a good way to determine the health and immunological compatibility of a mate. If it is good, hormone are released and you want to do it again, because you get a good response from the partner. This encourages mating with a good partner. 

Bad kisses do not release the hormone, and a single bad kiss early on can greatly diminish sexual attraction. A bad kiss can occur for a number of reasons, but an unpleasant hormone response serves as an early warning system for mating.