The Human Body


In adulthood, more permanent relationships, in the form of marriage or cohabitation, become prevalent. The frequency of sexual activity is different for different individuals. People in monogamous relationships often engage in sexual activity more frequently than those who have several partners. It is not unusual for some new couples to have sexual intercourse almost every day, but in general, among married or cohabiting couples, the frequency of sexual intercourse tends to decline the longer the two people are together.

As people age, they may experience physical changes, illnesses, or emotional upheavals, such as the loss of a partner, that can lead to a decline in sexual interest and behavior. In women, there is a gradual decline in the function of the ovaries and in the production of estrogen. The average age at which menopause (the end of the menstrual cycle) occurs is about 50. Decreased estrogen leads to thinning of the vaginal walls, shrinking of the vagina and labia majora, and decreased vaginal lubrication. These conditions can be severe enough to cause the woman pain during intercourse. Women who were sexually active either through intercourse or through masturbation before menopause and who continue sexual activity after menopause are less likely to experience vaginal problems. Women can use hormone-replacement therapy or hormone-containing creams to help maintain vaginal health. In men, testosterone production declines over the years, and the testes become smaller. The volume and force of ejaculation decrease and sperm count is reduced, but viable sperm may still be produced in elderly men. Erection takes longer to attain, and the time after orgasm during which erection cannot occur (the refractory period) increases. Medications and vascular disease, diabetes, and other medical conditions can cause erectile dysfunction.