Iris, a young woman from North Carolina, can't understand why she has no sexual desire -- she is only 30 and in love.
"It distresses me because I will marry soon and I know this will create a lot of tension in my marriage," Iris (not her real name) wrote to ABCNews.com.
Iris is one of an increasing number of women in the prime of life and at the height of their fertility who have lost their sexual desire, according to medical experts and a growing body of research.
Stress, depression and bad relationships can contribute to low libido, but often birth control pills or antidepressants are the culprit.
A 2010 study by the International Society for the Study of Women's Sexual Health found many young women experienced guilt and distress over their sex lives.
A cross-sectional study of 31,000 U.S. females 18 and older published in 2008 in Obstetrics and Gynecology magazine, about 43 percent of women reported sexual problems.
Of those aged 18 to 44, about 10 percent complained about low sexual desire -- or what is called hypoactive sexual desire disorder (HSDD), according to the study, Prevalence of Female Sexual Problems Associated with Distress and Determinants of Treatment Seeking (PRESIDE).
"It's a real diagnosis," said Dr. Carolyn Nemec, a women's health specialist in the department of family medicine at the Cleveland Clinic. "It's very surprising and we are missing the boat if we don't talk about younger women."
"We always think of it as something that women go through at menopause, but millions of American women are affected," she said. "It's a complex issue and women's libidos are complex."
In 2002, the American Psychiatric Association categorized HSDD in its Diagnostic and Statistical Manual of Mental Disorders (DSM) as any persistent lack of sexual desire that causes a woman distress.
The disorder was most common in women aged 45 to 64 at 14.8 percent.
It's not so much the lack of libido that characterizes the disorder, but the amount of anxiety it causes. Even though post menopausal women report less sexual desire, only about 8 percent are diagnosed with HSDD, because they are not distressed, according to the PRESIDE study.
"I think a lot of women are distressed out there and feel bad and think something is wrong with them," said Nemec. "The younger patients hear so much about menopause and a lot of these women -- aged 18 to 30 -- don't feel they have a voice. We need to focus on them."
Up to 40 percent of all women who have been diagnosed with HSDD also report depression, she said. And for those who are on antidepressants like SSRIs, as many as half can experience a decrease in desire.
Birth control pills that contain estrogen and progesterone can also be to blame.
"They increase sex-binding globulin, a protein in the blood stream that binds with our testosterone and testosterone is one of the central hormones in desire," said Nemec.
When she rules out all other causes of low libido, Nemec will often recommend trying a different antidepressant or decreased dosages. Sometimes, she'll ask the woman to go on a "drug holiday," to restart her libido.
For women, sexual desire is a complex psychological and physiological phenomenon.
Some of Nemec's patients are young women who have just had a baby and trying to reignite desire after a pregnancy. But others are single women in their 20s who began having sex just to keep up with their peers.