It’s post Valentine’s Day and the pressure is off..at least that might be thought of some couples. One day to celebrate romance, has come and gone but what if you are not feeling the love and lack desire for your partner? What could be wrong?

What happens when one partner’s desire level differs from another? Renee presented it this way. “It seems like all Chuck thinks about is having sex. I feel like that’s the only time he pays attention to me. After a rough day with the kids, I’m not exactly in the mood. But he seems ready to go any day of the week and oblivious to the household chaos. What’s wrong with me? At the beginning of our marriage, I couldn’t get enough of Chuck. Now, I just want a hot bath and some quiet!”

As a psychotherapist, I’ve treated many couples complaining of low sex drive or lack of passion in their relationships. Frustrated and even ashamed, they are bewildered as to how their once passionate feelings for each other dwindled to almost nothing. The immediate assumption is that something terrible is wrong in the relationship. There must be a deep hidden emotional problem that only Freud could understand! And if we can’t find that hidden problem, we can always blame our mothers!

In some cases, relationship issues are key to unlocking lost passion and renewing sexual interest. Men need to understand that women need to feel cared for, esteemed and emotionally connected to their husbands in order to deepen their sexual lives. Creating an atmosphere of relaxation is important to enjoying good sex as well. But for other couples, an understanding of the biology of desire is needed. It’s possible to be deeply in love with your spouse and have low sexual desire. Here’s why.

Desire differences are quite normal. Relationships usually begin with intense passion. You know, you overlook the fact that he can’t make a move without consulting his mother, or that he is really is obsessed with playing video games. You are in love and initial passion or infatuation does burn intensely. The reason this is true is because of the neurochemistry behind it.

According to experts, infatuation lasts about 18-36 months for most couples. Your hidden biology is thought to be the cause. Although theory is based on animal studies, research psychiatrist Michael Liebowitz at New York State Psychiatric Institute believes biochemical attraction goes this way: We meet someone to whom we are attracted. Our brains become saturated with a “love cocktail” composed of phenylethylamine (PEA-a naturally occurring neurotransmitter), dopamine (a neurotransmitter that stimulates libido), and other excitatory neurotransmitters. This natural amphetamine state is triggered by infatuation or what many of us call “romantic love”. To further give credence to this theory, a sexual medicine researcher named Theresa Crenshaw, documented elevated states of PEA in the bloodstreams of lovers and also in ovulating women.

What couples often fail to understand is that this burning fire of passion eventually reaches ember stage. The cool down, if not understood, can leave one feeling disillusioned and distressed.

Enter a second factor for couples to understand—the role of testosterone. This steroid hormone produced by both sexes correlates strongly with desire. After initial infatuation, a low testosterone woman can feel sexually disinterested. Men, on the other hand, have ten times the testosterone levels as women (Women have lower amounts but are more sensitive to the hormone). A man’s “T” level drops gradually with age but is genetically determined by the sensitivity of androgen receptors in the genitals. Typically, men have stronger desire than women. Of course, there are exceptions to this rule.

During the time of infatuation, PEA release is time-limited and sexual desire can be hidden because of the PEA release. Afterwards, testosterone levels play an important part in on-going desire. If you have a high “T” (testosterone) level and you are married to a person with a low “T” level – you may have problems.

The bottom line is that sexual desire may have more to do with hormones than previously believed. And this can be easily treated. Instead of assuming your relationship is deeply troubled, consider the role of biochemistry and talk to your physician.

Sustained sexual intimacy may have to be worked on for some couples. All couples face challenges when it comes to covenant endurance, but remember this: Passion is short-lived; sexual desire may be related to biochemical factors; and sustaining sexual interest is a complex phenomenon that includes your physical body as well as relationship factors.