Kissing is fun and it feels nice. But -- why do we do it?

According to new research, one big reason is that we need to size up our future mates.

The research, conducted by scientists from Oxford University, also explores the link between kissing and relationship quality, and differences in the value of kissing between men and women. The findings are published in two studies in the journal Archives of Sexual Behavior and the journal Human Nature.

"Mate choice and courtship in humans is complex," study researcher Robin Dunbar, a professor at Oxford, said in a statement. "It involves a series of periods of assessments where people ask themselves, 'Shall I carry on deeper into this relationship?' Initial attraction may include facial, body and social cues. Then assessments become more and more intimate as we go deeper into the courtship stages, and this is where kissing comes in."

For the study, researchers asked 900 people (308 men and 594 women), about half of whom were in long-term relationships at the time of the survey, what they thought about kissing and its importance in relationships, both short- and long-term. They found that in general, women were more likely than men to think that kissing is important in a relationship. People who rated themselves as attractive and people who had more casual or short-term romantic encounters were also more likely to assign kissing a high importance to a relationship.

Interestingly, the importance of kissing changed when looking at a short-term relationship versus a long-term relationship. Women were more likely than men to say kissing was more important in long-term relationships.

And what about timing of kissing with regard to sex? Researchers found that kissing was generally most important before sex, but then its importance decreased thereafter (it was rated as less important during sex, even less important after sex, and the least important during non-sex times). However, when researchers asked about kissing in the context of a committed relationship, it was rated as equally important before sex and during non-sex times.

Past studies have also affirmed the idea that smooching is a way to vet future mates. CNN Health reported on research showing that kissing provides sensory clues -- including taste, sound and smell -- that can help a person decide if he or she wants to kiss that person again.

"Kissing is not just kissing. It is a major escalation or de-escalation point in a powerful process of mate choice," Helen Fisher, a professor at Rutgers University and author of Why Him, Why Her: Finding Real Love by Understanding Your Personality Type, told CNN Health.

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  • Kissing Is Good For Your Teeth

    There's a reason a kiss is called a "wet one" -- smooching stimulates saliva production, which can actually <a href="" target="_hplink">wash harmful bacteria off the teeth</a>, Mathew Messina, D.D.S., told WebMD and <a href="" target="_hplink">reduce plaque buildup</a>, according to <em>Flickr photo by <a href="" target="_hplink">midiman</a></em>

  • Kissing Burns Calories

    Okay, so we're not talking the equivalent of a trip to the gym, but hey, every little bit counts, right? Locking lips can burn anywhere from <a href="" target="_hplink">two</a> to <a href="" target="_hplink">six calories a minute</a>, according to You're also putting a whole slew of <a href="" target="_hplink">facial muscles</a> to work when you pucker up, and just a few minutes of extra attention to those muscles can make a big difference when it comes to the appearance of frown lines or less-than-perky cheeks, according to the <em>Daily Mail</em>. <em>Flickr photo by <a href="" target="_hplink">{N}Duran</a></em>

  • Kissing Boosts Immunity

    There's no denying the fact that when you lock lips, there are bound to be some germs, uh, exchanged. One specific bug can be particularly hazardous to pregnant women, but researchers believe <a href="" target="_hplink">kissing is a way to introduce the virus to a woman in small doses</a> before she conceives, triggering her body to build up a resistance to it before she could ever pass it on to a child, according to Popular Science. However, if your partner in crime is visibly ill, it's still a good idea to hold off on that kiss, as it's still an <a href="" target="_hplink">easy way to catch mono</a>, strep throat and herpes, among other things. <em>Flickr photo by <a href="" target="_hplink">lejoe</a></em>

  • Kissing Eases Stress

    That feeling of relaxation post-kiss isn't all in your head. A small 2009 study measured levels of the bonding hormone oxytocin and <a href="" target="_hplink">the stress hormone cortisol in pairs of kissing college students</a>, the AP reported. Both men and women experienced a decline in cortisol, a sign of relaxation, that was much greater than when they just held hands. <em>Flickr photo by <a href="" target="_hplink">pedrosimoes7</a></em>

  • Kissing Could Ease Allergy Symptoms

    If those sniffles are due to seasonal allergies and not something contagious, it may be a good idea to go through with the smooch, after all. A small Japanese study found that couples who kissed for 30 minutes had <a href="" target="_hplink">lower levels of allergen-specific IgE</a>, the <a href="" target="_hplink">proteins that trigger pesky sypmtoms</a> like sneezing and sniffling. <em>Flickr photo by <a href="" target="_hplink">davitydave</a></em>

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