When you think about it, kissing is pretty weird. You’re basically rubbing the organ you use for eating and speaking against someone else's, an act that could be looked at as, well, gross. According to this video by The School of Life, it's precisely the taboo nature of kissing that makes it so exciting. It signals that you accept the other person to such an extent that you’re willing to do something otherwise quite repulsive with them.
This Video Explains Why People Kiss