Face and Mouth
Oddly, it all starts with a tilt to the right. Eighty percent of people angle their head that way when going in for a kiss.
You make contact and. . .sensory explosion! Lips are up to 200 times more sensitive than supersensitive fingertips.
Meanwhile, your nose is buried in his scent, which may be emitting subtle chemical attractants that could intensify your arousal.
A quick peck uses a couple of muscles, but kissing passionately engages some 24 facial musclesÃ¢â‚¬”plus 100 others in the body. (A fierce make-out might slay up to 100 calories.)
Your salivary glands begin their own workout, pumping out extra spit. During a real tongue twist, about nine milliliters of your saliva finds its way into his mouth (and vice versa). The gross news: That juice is teeming with as many as 1 billion bacteria. The better news: 95 percent of those are harmless.
If you're really into this dude, the kiss sends shock waves throughout your body that can increase blood flow to certain areas. Think stiffened nipples, fluttery stomach, tingling genitals.
Sensing the hubbub, the adrenal glands unleash adrenaline. Cue a pounding heart, heavy breathing, or sweaty palms. (If you two become a couple, kissing could eventually trigger an opposite effectÃ¢â‚¬”peace instead of passion.)
The physical thrill may prompt your brain to cue up dopamine, a neurotransmitter associated with pleasure. At the same time, other parts of your brain are shutting down negative emotions.
Your lip locking may also have prompted your pituitary gland (and his) to release oxytocin, the "bonding hormone." You two might already be forming an emotional attachment.
Any kind of make-out can reduce tension and hike happiness. Duos who kiss frequently are more likely to have long, satisfying relationships.
Sources: Justin R. Garcia, Ph.D., The Kinsey Institute at Indiana University; Marc Liechtung, D.M.D., Manhattan Dental Arts; Joseph Alpert, M.D., University of Arizona College of Medicine; Sheril Kirshenbaum, The Science of Kissing