The reasons why we respond with sexual feelings to people, circumstances, pictures, stories, movies, voices, and even smells are very complex. Hormones, including testosterone and estrogen, are just one factor in this complicated process.
Because our mind processes sexual information in complicated ways that are currently poorly understood, we may or may not have sexual feelings or thoughts and sexual responses in our bodies when we're faced with sexual signals. Past experiences, current mood, current distractions, self-image, and emotional needs all play a role in how we respond.
Women actually need testosterone to give a "green light" to a sexual response
A small amount of testosterone appears necessary for sexual feelings and sexual response. So, as long as all the other emotional factors are showing a "green light," testosterone allows the possibility of sexual feelings.
Estrogen is made from testosterone and any woman having menstrual cycles is making estrogen. Therefore, having menstrual cycles confirms that a woman is making normal amounts of testosterone. It is true, however, that testosterone levels peak during ovulation, so women who don't ovulate, particularly in the years just before menopause, may notice that their sexual desire is somewhat less easily triggered.
Women taking birth control pills also don't ovulate because the ovaries are mostly shut down by the pill. On the other hand, the pill itself contains a progestin along with an estrogen, and the progestin is similar in some ways to testosterone. Pills vary, however, in the specific hormones used - some have progestins with more testosterone-like activity than others.
What happens to testosterone levels after menopause?
After menopause, most women continue to make enough testosterone, and don't notice any particular change in the extent of sexual thoughts, dreams or fantasies, or their ability to respond to sexual stimuli.
Sometimes, however, especially with an early menopause or menopause suddenly brought on by surgery, radiation, or chemotherapy, women do notice a dramatic change. From the date of the menopause, they no longer have sexual dreams, nor do they think of stimulating themselves (masturbating), even if they did in the past. They also find it very difficult to respond to a partner, movies, a book, or indeed anything that once triggered sexual feelings and sexual thoughts. Any arousal is very slow and partial. Orgasms are much reduced in intensity or don't happen at all.
This drastic change is related to the hormonal disturbance from menopause. Women describe this change as being like "night and day" or being like "a light going out." Their bodies seem "sexually asleep" - sadly, some women say "sexually dead."
Can women with low testosterone take replacement therapy?
Yes, partial replacement of testosterone can be considered for women with an early and sudden menopause due to surgery or chemotherapy, in addition to their estrogen replacement.
For women with natural menopause, a very low level of testosterone is unusual, since the ovaries generally continue to make testosterone. Occasionally, though, it does happen - it's as if the ovaries are not there at all, even though they have not been removed by surgery or harmed by chemotherapy or radiation. In these situations, testosterone replacement may be helpful.
Estrogen also plays a role in sexual arousal
Estrogen is necessary for the genital response and probably also the breast response to sexual stimulation. Estrogen contributes to the complicated mechanism whereby the clitoris and other erectile tissue in the woman become filled with blood as the woman gets sexually aroused. If these tissues don't respond, the woman doesn't feel the sensations of warm, tingling fullness and genital stimulation is not pleasurable. This mechanism needs a minimum amount of estrogen.
At the same time, another mechanism fills the vaginal walls with blood and triggers the inner surface of the vagina to secrete a lubricating fluid. This mechanism also needs estrogen.
Then do women need to take estrogen after menopause to help with sex?
Not necessarily. The ovaries usually continue to make testosterone after menopause and, in some women, enough of this testosterone gets made into estrogen in the body's fat cells. But for others, especially those who are particularly thin, not enough estrogen is produced from testosterone in this way. Also, some women do not have any ovary tissue left because of surgery or chemotherapy.
Some women choose to take estrogen through their skin (in a "patch" or gel) or by mouth to reduce their menopausal symptoms, or to preserve bone density, or to prevent heart disease. Others choose to take supplemental estrogen only for the genital area, and use either a cream in the vagina or a ring that's placed high in the vagina and that has to be changed every 3 months. This last option is particularly useful for women who should not have any estrogen in their system, for instance, if they've had certain breast cancers.
Prolactin and thyroid hormone are also involved in sexual function
Prolactin is a hormone made by the pituitary gland at the base of the brain. In men, large amounts of prolactin often cause low sex drive. What happens in women is less clear, but high prolactin levels need to be treated anyway, because high prolactin can be associated with absent or irregular periods, or difficulty conceiving, sometimes with other symptoms such as headaches.
The correct amount of thyroid hormone is also necessary for sexual feelings and responses. Again, low or high thyroid levels need treatment in their own right and are diagnosed from other symptoms - very rarely the sexual ones. In women with underactive thyroid glands, the most common sexual symptom is lowered libido and lowered sexual response.