From Encyclopedia of Sex and Sexuality
The sex drive or one’s sexual appetite is commonly called “libido.” It is the first component of Helen Singer Kaplan’s triphasic sexual system—desire, arousal, and orgasm (see sexual response cycle)—and is a complex balance of physical and social factors. Researchers such as Alfred Kinsey and Masters and Johnson have suggested that the libido goes through periodic increases and decreases during one’s lifetime. The most frequent complaint about libido is usually heard when it is much decreased in relation to what a person feels is his or her normal level.
The physical factors affecting libido may include pain during intercourse (dyspareunia) from organic disease, illness, and erectile dysfunction. For example, dyspareunia can be caused by atrophy or thinning of the vaginal tissue after menopause (from loss of estrogen production), from infection, and from recent vaginal delivery. Endocrinal diseases such as diabetes mellitus and spinal injuries, as well as certain drugs, can affect a man’s ability to have and maintain an erection, and this may, in turn, influence libido.
The relationship between libido and sexual performance is complex and, as noted above, influenced not only by one’s physical condition but also by one’s emotional situation. Sexual dysfunction in both men and women is exceedingly common; over a lifetime half of all individuals will experience some sexual dysfunction, most often transient and situational in nature rather than indicative of serious underlying organic disease or psychopathology. If alterations in libido or sexual performance persist, appropriate medical evaluation and consultation should be sought.