The average person spends two weeks of his or her life kissing, according to data gathered by Statistic Brain. That means some kiss more. Some kiss less.

So why do people kiss? Scientists aren’t exactly sure. Romantic kissing exists in less than half of the world’s 168 cultures studied by scientists who published their findings in American Anthropologist.

In cultures in which romantic kissing is acceptable, it may function as a way for women to identify potential mates.

There is evidence suggesting women prefer the smell of men who are genetically different from them, perhaps enabling them to choose mates more likely to produce offspring who thrive.

While romantic kissing may have developed from less exciting survival instincts, it also makes us feel good. Our lips are designed with much greater sensitivity to touch than larger body parts. Researchers Wendy Hill and Carey Wilson at Lafayette College in Pennsylvania discovered in a study of heterosexual couples that kissing on the lips promotes the production of oxytocin, the same hormone that is secreted when breastfeeding. Oxytocin plays an important role in promoting affection and emotional bonding. It is often referred to as the “love hormone.”

Oxytocin and other hormones produced by romantic kissing boost our sense of happiness and well-being. Kissing on the lips also causes both men and women to experience a drop in cortisol levels, which lowers stress.

Romantic kissing might also improve a couple’s ability to cooperate. A German study demonstrated the power of kissing on the lips to synchronize couples’ brains.

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As Viktor Müller, co-author of the study, said, “I would suggest that kissing synchronizes our brains to produce a state or conditions for a better understanding of each other — or for getting in the right mood for partner-oriented behavior.” So passionate kissing may cultivate intimacy between committed partners by contributing to stronger empathy between them.

The longer they’re together, the longer many husbands and wives lose interest in passionate kissing. If they kiss at all, for some it becomes routine and is no longer exciting. For kissing to remain fun in a marriage, it’s necessary for couples to invest time and effort into building a foundation of mutual trust and a sense of safety in their relationship.

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Working together with your spouse to make kissing fun in marriage can be a gateway to great sex. In observing over 3,000 couples, marriage researcher John Gottman has identified and ranked in order of importance 13 things all couples do who have an amazing sex life.

Related: The Number-One Quality of Happy Marriages (You’ll Never Guess)

The first is to say “I love you” every day and mean it. The second: “They kiss one another passionately for no reason.”

If you want to get more fun out of kissing in your marriage, make it a priority to cultivate mutual trust and safety in your relationship. And consider a few other techniques to stir up passion.

The six-second kiss. Gottman recommends couples share a six-second kiss every day and calls it “a kiss with potential.” That doesn’t mean it’s a kiss that leads to sex. It may actually mean more if it doesn’t lead to sex — many wives don’t want to be kissed if every kiss is paired with the expectation that she responds sexually.

Related: What the Smartest Spouses Do

Consider the six-second kiss as a way of leaving the door open between you and your spouse for connecting emotionally as well as physically. Before you go your separate ways at the start of your day or reunite at the end of the day, treat yourselves to this stress-reducing kiss.

The eyes-open kiss. It’s been said the eyes are the window to the soul. So why do we always kiss with our eyes closed? Mix it up and kiss with your eyes open.

It may feel strange at first, but maintaining eye contact can help you stay in the moment, read your spouse’s cues, connect emotionally — and create a greater sense of intimacy.

Jon Beaty, counselor and father of two, lives near Portland, Oregon. He’s the author of the book “If You’re Not Growing, You’re Dying: 7 Habits for Thriving in Your Faith, Relationships and Work.”