A science geek's guide to locking lips (SHUTTERSTOCK PHOTO) With apologies to Louis Armstrong, a kiss is not just a kiss. Think of it as "a chemical choir," says science writer Sheril Kirshenbaum. In her new book, The Science of Kissing, the Austin, Texas writer weaves together classical history, evolutionary biology, psychology and scientific research to look at osculation (a fancy word for smooching). Kirshenbaum told me that the act of kissing involves a bunch of chemicals, all interacting together to make us feel a certain way. "We try to link our behaviour to one particular hormone or neurotransmitter, but there is a much bigger chemical picture." How so? To begin with, a romantic kiss prompts a rise in oxytocin (the love hormone) which is responsible for bonding and attachment. "It's part of the reason long-term relationships are maintained over time," Kirshenbaum explains. Oxytocin also spikes three to five times higher than normal during sexual climax. Dopamine is another kissing hormone that is involved with desire, a craving that makes you want to be with someone. That "cloud nine" feeling is due to dopamine's high: It's also likely responsible for extramarital affairs. Seratonin is the hormone that makes you continuously think about this person, Kirshenbaum says. And a bunch of silent odourless airborne signals called pheromones provide all kinds of insight into the other person. Don't forget cortisol, the body's stress hormone: Kissing reduces it. But doesn't deconstructing a kiss this way deter from its romance? "Not for me," she says. "I found it interesting that there is a strong chemical basis for why we feel the way we do -- to know how and why your body is responding." Hormones are only part of the story, however. Body language and the messages received by the brain can mean the difference between a half-hearted kiss and a passionate one. Setting the mood is step number one, and looking into a partner's eyes before kissing is also important. Research shows that two-thirds of us tilt our heads to the right in preparation for a kiss. Proper alignment also means priming our facial muscles for action. When we lock lips, five of our 12 cranial nerves switch into high gear, says Kirshenbaum. "During a passionate kiss, our blood vessels dilate and we receive more oxygen than normal to the brain. Our breathing can become irregular and deepen; our cheeks flush, our pulse quickens, and our pupils dilate." Kissing is a perfect example of behaviour that stems from both nature and nurture, she adds. "We kiss to express affection, adoration, respect and love. We kiss to celebrate new beginnings and to say goodbye. We kiss because we care, or want to appear to." In her view, a romantic kiss is nature's ultimate litmus test: "With it, we try to figure out how compatible we are with our partner, especially for women who are more sensitive to taste and scent and who need to be biologically more selective when choosing a partner." Kirshenbaum argues that kissing is a lost art that needn't lead to sex: "I could say that kissing is the more intimate behaviour of the two. It's being completely in someone's personal space where we are engaging so many more of our senses - touch, taste, smell - even more so than when we are having sex. That's why many prostitutes say they would have sex, but not kiss their clients." Lots of kissing is a telltale sign of a healthy relationship, says Kirshenbaum, a newlywed who married last summer. She views Valentine's Day as "one of those cultural reminders to pay more attention to the people we love. Kissing is a healthy behaviour. My research helped me really understand why it matters so much in a relationship." Be your kissable best Stinky breath can ruin the moment and even make the roses wilt, says Dr. Harold Katz, founder of the California Breath Clinics. Foods to avoid this V-Day: Milk chocolate and candy hearts. Candy hearts are full of sugar and mouth bacteria love sugar. Dark or semi-sweet chocolate fuel fewer bad breath bacteria than milk. Onions, garlic, cauliflower, brussels sprouts. Their high concentration of sulfur compounds exacerbate bad breath. Alcohol. Because it dehydrates, a kiss can be disgusting after a boozy beverage. To freshen your breath, drink a glass of water in between each glass of alcohol. Pucker up! Make your kisses count by following these tips from The Science of Kissing: Play up your assets. Red lipstick appeals to a very primal urge, but don't overdo it. Improve your taste and scent. Brush and floss daily; keep breath mints handy. Make kissing comfortable. Set the scene to ensure feelings of security and trust. Learn the power of touch. Hugging, hand-holding and caressing a partner's back or face sends pleasurable signals to the brain. Famous kisses "The first kiss I had was the most disgusting thing in my life. The girl injected about a pound of saliva into my mouth and when I walked away I had to spit it out." Actor Leonardo Di Caprio. "People who throw kisses are hopelessly lazy." Comedian Bob Hope. "A man's kiss is his signature." Actress Mae West. "I married the first man I ever kissed. When I tell this to my children they just about throw up." Former First Lady Barbara Bush. "I would rather just make out and kiss someone instead of sex." Socialite Paris Hilton. "If you kiss on the first date and it's not right, there will be no second date." Actress Jennifer Lopez. A kiss is just a kiss Though written in 1931 by Herman Hupfeld, this famous line that starts the chorus from the song As Time Goes By is widely remembered from the 1942 Humphrey Bogart movie Casablanca. The song, recorded by many artists including Louis Armstrong, Rod Stewart and Willie Nelson, has been voted one of the top ten best songs from films. Here are its most quoted lines: "You must remember this, A kiss is just a kiss, a sigh is just a sigh. The fundamental things apply, as time goes by. And when two lovers woo, they still say, 'I love you,' On that you can rely. No matter what the future brings, as time goes by."