Editor's Note: Dannah Gresh is author of What Are You Waiting For? The One Thing No One Ever Tells You About Sex.

By Dannah Gresh, Special to CNN

Recent studies have revealed some good news in the sex culture among college co-eds: there are more virgins among them now than was the case a few years ago.

These days, 29% of females and 27% of males between ages 15 and 24 claim to be virgins, up from 22% of both sexes in 2002, according to the Centers for Disease Control.

But among the college students who aren’t abstaining, we’re seeing more sex, thanks to casual hookups. According to recent research from Stanford University, the majority of college co-eds are still having sex, with an average 9.7 sexual partners for men and 7.1 for women.

Thankfully, we have more scientific information about casual sex than our parents did when they drove their Volkswagen buses to Woodstock for a dose of the sexual revolution. They wanted to think—as many of those cruising along the New Millennium highway still do—that we can engage in the act of sex without the emotion.

"Emma wants a relationship without the relationship. She just wants the sex,” actress Natalie Portman said of her role in the recent movie "No Strings Attached." “…I’m tired of seeing girls who want to get married all the time and that's all they're interested in. I think there is a wider vision of how women can conduct their lives and what they want."

Sounds so easy.

Just like the hippie culture found a pill that conveniently removed the “inconvenience” of pregnancy, today’s hookup culture believes it has found a recipe for removing the inconvenience of emotion: friends with benefits.

Scientifically, though, that’s impossible. We know that thanks to what neuroscientists have learned about a walnut-sized mass in the brain called the deep limbic system.

The deep limbic system stores and classifies odor, music, symbols and memory. In other words, it’s a place for romance, capable of processing a splash of cologne on your lover’s neck, a particular iPod playlist or a bouquet of red roses.

The brain chemicals associated with romance and sex wash over the deep limbic system during a wide variety of sexual experiences, according to research from the Medical Institute for Sexual Health.

Holding hands, embracing, a gentle massage and, most powerfully, the act of sexual intercourse work together to create a cocktail of chemicals that records such experiences deep into the emotional center of your brain.

It’s why we remember sexual experiences and images so clearly.

One of the critical neurochemicals released during sex is dopamine. Dopamine makes you feel good; it creates a sense of peace and pleasure. Anytime your body experiences pleasure, whether it’s good for you (working out) or bad (doing crystal meth), the limbic system gets washed in dopamine.

In essence, it is a “craving” chemical. It makes you want more. It creates addiction. Dopamine attaches you emotionally to the source of pleasure.

Another critical sex hormone is oxytocin, the subject of recent books like "The Chemistry of Connection: How the Oxytocin Response Can Help You Find Trust, Intimacy and Love." The chemical is released during sexual expression. A tiny dose is downloaded during intimate skin-to-skin contact; a much bigger dose is released during orgasm.

In fact, the only other time as much oxytocin is released as during orgasm is when a mother is breastfeeding her baby. The mother feels its release and is bonded to her child, and the baby’s brain learns for the first time to enter into relationship by connection. I’d say the chemical’s job is to bond us for life.

The knowledge of sexual bonding is nothing new.

“Do you know that he who unites himself with a prostitute is one with her in body?” the apostle Paul wrote in the New Testament. “Do you know that he who unites himself with a prostitute is one with her in body? For it is said, ‘The two will become one flesh.’”

Christian author Lauren Winner translates those verses this way: “Don’t you know that when you sleep with someone your body makes a promise whether you do or not?”

The bottom line is that you get “addicted” and “bonded” to the people you have sex with, even if they are “just friends.”

That helps explain why Stanford sex researcher Paula England has said that “Some people are hooking up a bunch of times with the same person but are not calling it a relationship.” Maybe these people are not as unattached to their “friends” as they would like to think.

Here’s where the hookup culture starts to be a problem. What happens if you get caught up in the friends-with-benefits-game and have multiple partners? What happens when the partners you’ve become addicted and bonded to are gone?

You experience withdrawal symptoms in the emotional center of the brain.

Young women, especially, are likely to spiral into a depression when the source of their addiction isn’t interested in another hookup. A 2003 study from the conservative Heritage Foundation found that 25.3% of sexually active teenage girls experienced depression, compared to 7.7% of sexually abstinent girls.

The study found that 14.3% of sexually active girls attempted suicide, compared to 5.1% of their virgin peers.

And when a person graduates from the hookup scene and tries to have an intimate relationship with the person they want to spend the rest of their life with, things can get complicated.

There are already a lot of other people he or she will be addicted to, and that creates more chaos for the exhilarating but challenging task of building a life of intimacy together. The Kinsey Institute notes that one of the five factors that predict infidelity in a relationship is “having had a high number of prior sex partners.”

Casual sex is happening. We shouldn’t ignore it. That’s especially true of the faith community. But when we talk about it, we should use science. There’s nothing biologically brief about a hookup.

In the interest of full disclosure, my motivation here is my Christian faith. I believe sex to be an incredible gift from God, meant to transcend the physical to discover something emotional and spiritual with another person.

But since my faith may alienate some of you from my message, I ask you not to think too hard about religious differences. Stick to the facts.

The good news is that we are seeing an ever-so-small rise in the number of young people choosing abstinence.

What are they waiting for? Some mind-blowing pleasure and an incredible intimacy–without all the baggage of a broken heart.

The opinions expressed in this commentary are solely those of Dannah Gresh.