By Jay Dixit, published on July 1, 2009 - last reviewed on November 20, 2015
Romantic love has three components—romance, attachment, and sexual arousal—and kissing activates all three, says Helen Fisher, author of Why Him? Why Her? Both men and women also kiss to assess genetic compatibility. That's why kissing someone new can create sparks—or cause a budding romance to wither on the branch. We determine compatibility largely via scent, but saliva exchange may well play a role as well. Maybe that's why 66 percent of women and 59 percent of men have experienced a first kiss with a new person that instantly killed the attraction.