Oral Fixation: The disgusting science behind locking lips

By Nicole Caldwell for Thrillist

The science of kissing is called Philematology, and it’s just as unsexy as it sounds.

When you swap spit with unsuspecting partners, you’re sharing more than you think. For every 10 seconds spent at first base, you transfer 80,000,000 bacteria from one mouth to another. The cleanest mouths among us harbor between 1,000 and 100,000 bacteria on the surface of each tooth. Those of you not brushing and flossing on the regular are providing sanctuary to anywhere from 100 million to 1 billion bacteria on every single one of your (not-so) pearly whites. Hosting that kind of liveliness in a space kept at a humid 95-ish degrees makes our mouths the “tropical rainforest” of the body.

While lips may be our largest-exposed erogenous zone, the nasty stuff lurking on the surface of that area is a serious turn-off.

Each adult human has about 400 different species of microorganisms living in his or her mouth, waiting to be shared. Tonsil hockey is a primo vehicle for “contact spread” -- the transfer of disease through direct, contaminated touch. But there’s more! “Droplet spread” is also super easy while making out because of orifices like the eyes, nose and mouth.

17th century Dutch scientist Antony van Leeuwenhoek is the man first credited with the detection of oral bacteria. He found the little buggers -- animalcules, as he quaintly called them, in cultures he drew from his own teeth. That discovery would eventually lead to our awareness of this terrifying laundry list of what can be spread during an otherwise hot make-out sesh:


  • Meningococcal Disease (meningitis)

  • Streptococcus (can lead to strep throat, tooth decay, and gum disease)


  • Coxsackie Virus (hand, foot and mouth disease)

  • Cytomegalovirus

  • Flu

  • Hepatitis B

  • Herpes

  • HIV (if your partner has an open sore in his or her mouth)

  • Mono (glandular fever)

  • Respiratory Infections

  • Warts

If kissing can cause so much damage, why are we evolutionarily hard-wired for the activity? Our lips are extroverted; puckered out. They’re loaded with nerve endings that send all kinds of confusing signals to other body parts. Smooching brings into play five of our 12 cranial nerves; firing off electric impulses that make us drunk with warm and fuzzy feelings. There’s only one other animal on earth kissing like humans do: the bonobo ape, which seems comical until you realize bonobos and people are about 99% similar.

Some scientists think kissing evolved from mouth-to-mouth food transference, which is how we used to feed each other -- giving new meaning to the phrase, “You eat like a bird.” Others believe kissing is a way for our DNA to seek out desirable genes; evidenced by certain scents and tastes. By design, our major histocompatibility complex (MHC) genes push us to pursue people with genes different from our own.

And kissing has health benefits: stress reduction, metabolism booster... sucking face even improves saliva flow which can help to keep a healthy mouth. In face, locking lips can actually help build immunity to non-life-threatening viruses and bacteria which, in the long run, might help you stave off disease.

No bets placed, though, on what you’ll catch in the process.