Libido and Testosterone
Lack of interest in sex is often called decreased libido or decreased desire. Libido is governed by psychogenic factors and involves all five senses (sight, smell, taste, touch, and hearing) as well as hormonal factors. Low libido, or hypoactive sexual desire, occurs in about 15% of men and in about 20% of the general population, both men and women. Depression and anxiety may adversely affect one's libido, and depression is the leading cause of hypoactive sexual desire. Other causes of hypoactive desire include relationship factors: lack of trust, intimacy conflicts, and lack of physical attraction to one's partner. The hormone testosterone is the main hormone responsible for libido in men. Testosterone levels have an effect on libido and on sexual thoughts and fantasies.
Sexual arousal requires input from nerves and arteries. To achieve an adequate erection, there must be at least a six-fold increase in blood flow into the corpora cavernosa. Changes in nerves, arteries, and veins may lead to trouble with erections.
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What causes decreased Libido?
Your interest in sex is governed by sex hormones (substances responsible for secondary sex characteristics, e.g., hair growth and voice change in males), primarily testosterone, and by psychosocial factors. Low testosterone levels are associated with decreased libido. Stress, depression, or anxiety may also affect your libido. In men with erectile dysfunction, interest in sex may be diminished as a result of their inability to achieve an adequate erection.
Any man with decreased libido should have his serum testosterone level checked. Normally, there is a "feedback loop" between the brain and the testes (two male reproductive organs that are located within the scrotum and produce testosterone and sperm). The brain, through the release of a chemical called luteinizing hormone (LH), tells the testicles to produce testosterone. The production of testosterone by the testicles acts on the brain to decrease the release of LH. If the testicles don't produce enough testosterone, the brain releases more LH in an attempt to stimulate the testicles to produce more testosterone. If the brain does not release enough LH, the testicles wont produce enough testosterone. This problem may occur in men with brain rumors or congenital abnormalities.
Another problem that can affect testosterone production is overactivity of the pituitary gland. The pituitary gland is a gland in the brain that is composed of two parts, the anterior lobe and the posterior lobe. The anterior lobe produces such hormones as luteinizing hormone and prolactin. Overactivity of the pituitary gland can be caused by a pituitary adenoma (benign [noncancerous] tumor of the pituitary gland). This abnormality can lead to an elevated prolactin level, which in turn suppresses testosterone production. Abnormalities of the testicles themselves that lead to impaired function of the testes may cause the testosterone levels to be low. Such abnormalities may include a history of testicular torsion, a prior history of undescended testes, prior testicular infections, and other congenital anomalies that affect the testes. Removal of both testes (bilateral orchiectomy) for prostate cancer or (rarely) bilateral testicular cancers causes a significant drop in testosterone level and decreases libido. Men with a single testis usually have adequate testosterone production, provided that the remaining testis is normal.
Testosterone levels do decrease as one ages, but this does not usually cause problems with libido.