What’s in a kiss? Here’s what the latest science shows, according to Sheril Kirshenbaum, who wrote the book The Science of Kissing:

• First know this: A kiss serves as one of the first tests of your relationship. Because a new survey by The State University of New York shows that more than half of men and women have ended a relationship because of a bad kiss. Why?

• Kirshenbaum says it partly boils down to chemistry, since we transmit a small amount of DNA in our saliva. And research shows that we subconsciously pick up on cues about a person’s reproductive potential through their kiss. 

• Also: Kissing triggers ALL of your senses. That’s because half of the major nerves in your head connect to the lips! So, for example: Your sense of smell kicks in to detect if your partner has poor hygiene, which can be a sign of disease. Your vision may also go blurry, because when your pulse quickens, your pupils go wide, which is why many people close their eyes when they kiss.

• Then there’s your sense of touch. Kirshner says when your lips touch someone else’s, electric signals bounce between the mouth, skin and brain - triggering the release of dopamine. That’s the brain’s feel-good chemical that gives you a natural “high,” similar to having an addiction. That’s why a great kiss can leave you feeling euphoric, and a bad kiss can spoil your appetite. 

In other words: Our expert says kisses provide powerful clues to help decide when to pursue a relationship, and when to turn around and run.