This year, we celebrated our 25th wedding anniversary. So, last week, one evening, I told my wife about a news story I heard on National Public Radio (NPR) about the microbiology of a kiss. My wife smiled.

A group of researchers, I said, looked at the oral bacterial flora of 21 couples to determine how many bacteria were transferred by a kiss. One partner was given a yogurt with specific bacteria and then the couples were asked to kiss, and then the mouths were swabbed and cultured.

Lead researcher Remo Kort told NPR that a modest kiss — like the one you give when you go to work — transfers about 1,000 microbes. A longer 10-second “intimate deep kiss” — the one you give after coming back from a long business trip — that can transfer up to 80 million bacteria. Wow!

We may not realize it, but our body harbors trillions of bacteria and for the most part they are more often beneficial than harmful. Bacteria help us digest our food, prime our immune system and prevent bad bacteria from making us seriously ill.

What researchers are now discovering is that the variety of bacteria we become colonized with is constantly changing and that often it is impacted by the people we are in close contact with in our lives.

My wife would not have any of this explanation. “Keep your cooties to yourself,” she said, still smiling. Cooties aside, many people may not know that kissing has crucial behavioral, biological, and psychological purposes.

Studies have shown that the first kiss is for “mate assessment” while subsequent kisses are for “mediation of feelings of attachment in long-term relationships.”

Biologically, kissing serves another purpose. Our mouths have some 700 varieties of bacteria and research shows that the greater the diversity, the better it is for our health.

Yet if we set aside the microbiology of kissing — the psychology of kissing has shown to be even healthier and lucrative. A study quoted in the book “The Science of Kissing” (yes, there is such a book) cites a German study from the 1980s where “men who kissed their wives leaving for work lived, on average, five years longer, earning 20 to 30 percent more than peers who left without a peck good-bye.”

Interestingly, men who did not kiss their wives before leaving for work had a 50 percent increased possibility of a car accident. Before you begin each day locked in a passionate smooch, it’s worth pointing out that there may be many confounding factors that may lead a man to kiss or not kiss his wife before he goes to work. But it is good to credit the kiss.

Yet, my wife did not seem phased by my convincing arguments. “Why are you still smiling?” I asked.

“Because I heard the same story on NPR,” she said, “and I didn’t think about the bacteria. I thought about you.”

Manoj Jain is an infectious disease physician and contributor to the Washington Post and The Commercial Appeal.  He can be reached at his self-titled site, Dr. Manoj Jain. This article originally appeared in The Tennessean.

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