Why Women Have Sex (23 page)

Anatomical differences between men’s and women’s genitals also can impact differences in desire. When men become aroused, their erections provide very visible and direct feedback that prompts an urgent desire for sex. This can happen even when they do not initially seek sex. Nightly erections often occur during REM, or rapid-eye-movement, sleep, the period of the sleep cycle when brain waves slow down and people dream. Men also get erections from accidentally brushing their penises with clothing or in the shower—without the need for conscious sexual thought. The feedback they receive from having an erection, though, can easily change a nonsexual event into a sexual one. Women, on the other hand, receive very little feedback from their genitals when they first start to become
aroused. Thus, genital arousal cues do not trigger women to want sex as frequently or in the same way as they do for men.

For men, sexual thoughts, images, or fantasies can also cause erections that can make them want to have sex. Sexual fantasies can also make women want to have sex. Many studies find that women report less frequent sexual fantasies than men, although estimates vary from study to study. In men, estimates range from five sexual fantasies per day to one per day. In women, estimates range from three per day to less than once per month. Interestingly, when sexually compulsive men are treated with drugs that decrease testosterone levels, they report lowered levels of sexual thoughts and fantasies. So perhaps higher testosterone levels cause men to fantasize and think about sex more than women. To the extent that sexual thoughts and fantasies create the desire to have sex, women have fewer of these sexual desire triggers than men.

While some couples start out with different levels of sexual desire, others are compatible in their levels of desire for long periods of time until something happens to diminish one partner’s drive. One woman in our study described it matter-of-factly:

Having been with my previous boyfriend for three years, our sex life declined due to my disinterest. At times his discontent with the situation was so overwhelming and disruptive to the rest of our lives that I would feign interest and have sex with him just to make him happy, in part because I felt I wasn’t holding up my end of the relationship sexually.

—heterosexual woman, age 21

Many factors can contribute to low sexual desire in a woman. Some are short-term and contextual, such as feeling too tired after work or child care or not having the privacy to feel comfortable having sex. Others are more enduring and can lead to relationship distress. These include biological causes, such as changes in hormones, pregnancy,
medications, or health, and relationship factors, such as decreased attraction to a partner, sexual boredom or frustration, and conflict with a partner. Let’s first consider the biological causes.

There are three major categories of “sex hormones”: progesterone, estrogen (which comes in three different varieties—estriol, estradiol, and estrone), and the androgens (of which testosterone is the most important). Progesterone is primarily known for its role in pregnancy. It is responsible for “building the nest” by preparing the lining of the uterus for implantation of the fertilized egg. Studies have not shown progesterone to play an important role in women’s sex drive, although high levels cause the symptoms of PMS, or premenstrual syndrome—a common desire killer.

Estrogen and testosterone, on the other hand, are critical for women’s sexual interest. Estrogen, in addition to protecting the bones and heart (and presumably helping women to remember where they put their keys), is responsible for the vaginal lubrication that occurs when a woman feels sexually aroused. It also helps “plump up” and maintain women’s genital tissues. Without estrogen, vaginal intercourse and stimulation of sensitive erogenous zones such as the nipples and clitoris would be painful.

Testosterone, generally considered the “male hormone,” might actually play the most important hormonal role in women’s sex drive. Like estrogen and progesterone, women’s testosterone is produced primarily by the ovaries and a smaller portion by the adrenal glands. According to medical laboratories, the “normal” range of free testosterone for women aged eighteen to forty-six is anywhere from 1.3 to 6.8 picograms—that is, 1.3 to 6.8
trillionths
of a gram—per milliliter. That’s obviously very little, and just by comparison, beginning at puberty the male testes produce somewhere between 300 and 1,000 picograms per milliliter daily.

Testosterone levels decline naturally year by year in women starting around age twenty. But the biggest drop in testosterone occurs around the time a woman undergoes menopause, usually when a woman is in her mid-forties to fifties, and her ovaries dramatically decrease hormone production. It is generally believed that a woman’s testosterone levels decrease by about 50 percent between the ages of twenty and fifty. If a
woman has a total hysterectomy that includes having both ovaries removed, regardless of her age, testosterone production is dramatically decreased. As one woman in our study noted, this can negatively impact drive:

After thirty-two years, it’s hard to think of a single instance [of having sex when I wanted to]. I think it just happens in long-term relationships. In my case, a hysterectomy lowered my libido. There were times when I did not feel like having sex, but just did it for my husband. It was frustrating not to want to do it, and depressing when I did it because it was not fulfilling for me. However, I felt guilty for not having sex as often and wanted to please my husband, so there you have it.

—heterosexual woman, age 52

There is no doubt that a certain amount of testosterone is required for women to experience sexual desire. A lack of testosterone negatively affects how frequently a woman masturbates, fantasizes about sex, and desires sexual activity. Women who lack sufficient testosterone may also lack sensation in their nipples and clitoris, and are unable to become sexually aroused even when stimulated by someone or something that used to turn them on.

How much testosterone is enough? Unfortunately, nobody really knows. The link between testosterone levels and women’s sex drive is not straightforward. Although labs give ranges of what is “normal,” women vary a lot in how much testosterone they need to feel good. For example, two thirty-five-year-old women could have exactly the same levels of testosterone and one could experience a healthy sex drive while the other complains of diminished desire. This may be related to what the women’s testosterone levels were in their late teens compared to their current levels. Adding to the confusion, there are many women who complain of a lack of sexual desire and have perfectly normal testosterone levels, and there are many women who have low testosterone but high sex drives! Sandra Leiblum, a sex researcher, therapist, and author of several books on women’s sexuality, suggests that if a woman used to experience sexual desire and no
longer does, she should have her blood levels of dihydroepiandrosterone (DHEA) and testosterone checked by her gynecologist or an endocrinologist. If the levels fall within the lowest quarter of the “normal” range for her age, she recommends testosterone replacement therapy.

Testosterone is available by prescription in many forms—pills, lozenges, capsules, and, most commonly, creams that are applied to the clitoris and inner labia. There has been some convincing research that taking testosterone helps restore sexual drive in women with abnormally low levels, and it has been especially effective for restoring drive in postmenopausal women. Testosterone is also available over-the-counter in the form of DHEA, which converts to testosterone once it is in the body. The standard recommended DHEA dose is 50 to 150 milligrams per day, taken each morning. It usually takes a few months of regular use before a woman will be able to feel any changes. However, women who try DHEA as a means for boosting their testosterone levels should know that the production of DHEA, like that of many herbal supplements, is not regulated by the U.S. Food and Drug Administration. As a result, although the bottle label may say the capsules contain a certain amount of DHEA, with some brands the actual amounts may be quite different.

It is important to keep in mind that if a woman has low desire but normal levels of testosterone, then increasing testosterone is not going to help increase her sex drive. There are also potential negative consequences of taking testosterone when the body already has enough of its own. Too much testosterone in a woman can put her at risk for liver damage and can lead to the development of facial hair, acne, hair loss, and even the deepening of her voice. These are not generally considered sexy changes, so unless the plan is to decrease her partner’s desire to have sex with her, caution must be exercised.

Women’s sex drive can change dramatically during and following pregnancy. Some of the reasons are tied to the emotions of expecting.
These include a couple’s level of excitement about the pregnancy, the severity of morning sickness or trouble with sleeping, how sexy a woman feels about her ever-expanding body, and whether the couple is worried about the baby’s eye being poked by the penis (which can’t happen, by the way).

A series of hormonal changes also accompany pregnancy. Estrogen and progesterone no longer fluctuate the way they do prior to conception. They are both simultaneously high to get the woman’s body ready for milk production and to keep the uterine lining thick to prevent miscarriage. High levels of estrogen may make a woman feel sexually aroused and interested, but high progesterone may make her too tired and cranky to want to do anything about it.

After childbirth, a woman’s sex drive is a lot more likely to decrease than increase, at least for a short time:

I had given birth to our son a few months prior and still did not have any sexual drive.
We
had not had sex since before our son was born and I felt guilty about not being interested. So I pretended to be interested and had sex.

—heterosexual woman, age 35

This is not surprising given the lifestyle and hormonal chaos that often occurs in those first months. Most women have either vaginal soreness from childbirth or pain and tenderness from cesarean surgery. Most are exhausted from the lack of sleep associated with trying to feed and accommodate a new person into the couple’s life.

Hormones once again change dramatically, impacting mood, sleep, and sex drive. With breast-feeding, levels of oxytocin increase—but most likely it is facilitating mother-child bonding rather than bonding with a sexual partner. At the same time, estrogen levels decrease. Because estrogen works with brain chemicals to maintain a sense of well-being, a drop in estrogen can dampen mood and may contribute to postpartum depression.

The oxytocin released during breast-feeding also suppresses testosterone levels, so it could negatively impact women’s sex drive. From
an evolutionary perspective, both the decrease in sex drive following childbirth, and the fact that the hormonal changes during breast-feeding make conception less likely, serve an important birth-spacing function. Ancestral mothers who had children too closely spaced often found their limited resources spread too thin. A temporary decrease in sexual desire helped ensure adequate spacing between children and hence a better chance that the children survived and thrived. Indeed, in traditional cultures, the typical birth spacing is about three and a half years.

How soon it takes for sex drive to return after childbirth depends on a lot of factors, not the least of which is how long it takes for a woman to feel less sleep deprived and more in control of her life:

Being in a relationship for any amount of time, mine being almost six years, there are times when I just don’t feel like having sex. I have two children, one two years old, the other one year old, and after I had my daughter (the one-year-old) I was just so tired from being up all night feeding her and taking care of both of the kids during the day, I just wanted to go to bed and sleep, not have sex. But just because at that time my sex drive wasn’t what it used to be didn’t mean my fiancé’s had slowed down any. He was definitely in the mood, kissing my neck, rubbing his hands gently up and down my body, caressing me, doing everything he knows I love, and I was just too tired to react the way he wanted me to, but I didn’t want to hurt his feelings and I just felt it was my duty to give him sex when he wanted it, so I did.

—heterosexual woman, age 22

For a small group of mothers, their sex drive never returns to pre-pregnancy levels, often because the couple moves into parenting mode at the expense of their romantic relationship. Some women get so wrapped up in parenthood that being a mother becomes their primary or sole identity. Planning nutritious snacks for school supplants sexy lingerie and naughty whispers in bed at night. Unless these women’s partners continuously remind them, years could pass before they would
realize their sex lives no longer exist. When they finally do, the relationship may have become so practical that both partners have forgotten how to feel sexual desire for each other. In rare cases there may also be a physiological explanation. Some researchers believe that pregnancy can sometimes permanently impair the production of testosterone, and that, in turn, could permanently affect a women’s desire to have sex.