Story highlights Low desire in one partner is one main reason couples seek out sex therapy

Sexual desire changes across long-term relationships

Ian Kerner is a licensed psychotherapist, certified sexuality counselor and New York Times best-selling author. Read more from him on his website, iankerner.com.

(CNN) About 15% of men and 34% of women say they're not really interested in sex, according to a new study, statistics that few experts find surprising. In fact, low desire in one partner is probably the top reason couples seek out sex therapy.

When one of you has more interest in sex than the other, it's easy for the person with the higher sex drive to feel rejected, bruised and undesirable and for the partner who avoids sex to feel pressure, anxious and guilty.

Any number of factors can affect sexual desire, and most of them have little to do with your partner's attractiveness. In the study I mentioned, researchers found that for both men and women, physical and mental health had an impact on libido. But they may have different motivations for avoiding sex.

"For men, it's often the appearance of disinterest rather than actual loss of interest," sex therapist Deborah Fox said. "Men avoid sex frequently due to prior performance issues, such as erectile issues or rapid ejaculation. They may avoid it to escape the anxiety of these issues reoccurring." In women, hormonal factors and fatigue can contribute to low libido.

And sometimes, life just gets in the way. "In my practice, I see a lot of desire diminish due to interest in porn, boredom of the same sexual routine, the comfort of monogamy and relationship security, and the loss of couple time due to a focus on parenting time," sex therapist Amanda Pasciucco said.

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