Procreation through sexual activity is an adaptive evolutional response, which gives the species a high potential for survival. Sexual behavior — a much wider subject — is, however, a learned behavior. In mammals and non-human primates, it is controlled by instincts with timing dependent on the estrus cycle of the female. By contrast human sexual behavior is influenced by the family, sociologic factors (mass media, community institutions and social milieu), individual experience and choice.

Even though sexual behavior and attitudes toward sex vary greatly among individuals, the desire for sexual pleasure is thought to be strong in most men and women. It should be noted that sex for satisfying sexual hunger is only one reason for sexual experience. Other reasons for having sex with a partner, and particularly important for women, are: (1) to enhance emotional closeness, bonding, commitment, sharing and tolerance; (2) to show love and affection; or (3) to let the partner see that he/she has been missed (emotionally and/or physically). There is no consensus regarding terminology for the force that makes us initiate or respond to sexual behavior, but commonly used terms for it are libido, sex drive and sexual desire. Another definition of libido is: the force by which sexual instinct is represented in the mind. Libido is a word of Latin origin and means pleasure, lust, desire.

Some researchers make a distinction between sex drive and sexual desire. For them sex drive is an omnipotent force that can lead to all forms of sexual outlet: sexual fantasies, masturbation, intercourse. Sexual desire is defined as the sexual drive toward a particular sexual outlet, i.e., intercourse with husband in preference to masturbation. This divide may be quite unnecessary and most people (professionals or lay) use libido, sex drive and sexual desire interchangeably. The frequency and intensity of sexual desire and sexual activity and the degree of sexual satisfaction vary throughout one’s life. Nevertheless, the phases of the sexual response cycle remain the same and do not change. Meaningful discussion about sexual dysfunction is impossible without being thoroughly familiar with the phases of the sexual response.

Phases of the sexual response cycle

Aging and the sexual response

The speed and intensity of the vasocongestive response decreases with aging. There is a reduction in the elasticity of the vaginal wall and the size of the vagina itself. Vaginal lubrication is slower and less marked and breast changes are less noticeable. Orgasm in older women is associated with fewer contractions and occasionally may be painful. The resolution phase is more rapid in older women. These changes become increasingly prominent after the menopause and some are related to estrogen and/or testosterone deficiency. There is an increased latency to excitement and greater need for longer tactile stimulation and an increased refractory period (Table Factors associated with aging that adversely affect sexual response). Longitudinal data show that, for healthy women, aging is not associated with decreased sexual desire or decreased orgasmic capacity. Aging may be associated with quantitative but not qualitative changes in sexual activity.

Table Factors associated with aging that adversely affect sexual response

Physical deconditioning
Chronic disease(s)
Increased use of medication
Age-related emotional problems
Situational
widowhood
nursing home environment
Expectations
society
personal
Previously low sexual activity

Epidemiologic observations

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