Male infertility refers to a male’s inability to cause pregnancy in a fertile female. In humans it accounts for 40-50% of infertility. It affects approximately 7% of all men. Male infertility is commonly due to deficiencies in the semen, and semen quality is used as a surrogate measure of male fecundity.
Over their lifetimes, approximately one in every five couples in the seeks infertility care. Surprisingly, only half of couples who are trying to become pregnant achieve pregnancy easily and about one in ten  couples of reproductive age are involuntary infertile; male infertility accounts for half of these cases.  Despite the relative importance of infertility due to the male, infertility evaluations have traditionally focused on women, because women tend to seek gynecological care and because men often are reluctant to seek advice.
A variety of disorders ranging from hormonal disturbances to physical problems, to psychological problems can cause male infertility.  Although many treatment options are now available, in many cases treatment will not work.  In many instances, male infertility is caused by testicular damage resulting in an inability of the testicle to produce sperm.  Once damaged, the testicle will not usually regain its sperm-making capabilities; this aspect of male infertility is analogous to menopause (though not natural like menopause) for women and cannot usually be treated.  Despite medicine’s limited ability to treat male infertility, many successful treatment options are available for its many causes.  Besides testicular damage, the main causes of male infertility are low sperm production and poor sperm quality.
The Causes of Male Infertility
Male infertility has many causes–from hormonal imbalances, to physical problems, to psychological and/or behavioral problems.  Moreover, fertility reflects a man’s “overall” health.  Men who live a healthy lifestyle are more likely to produce healthy sperm.  The following list highlights some lifestyle choices that negatively impact male fertility–it is not all-inclusive:
Smoking–significantly decreases both sperm count and sperm cell motility.
Prolonged use of marijuana and other recreational drugs.
Chronic alcohol abuse.
Anabolic steroid use–causes testicular shrinkage and infertility.
Overly intense exercise–produces high levels of adrenal steroid hormones which cause a
testosterone deficiency resulting in infertility.
Inadequate vitamin C and Zinc in the diet.
Tight underwear–increases scrotal temperature which results in decreased sperm production.
Exposure to environmental hazards and toxins such as pesticides, lead, paint, radiation, radioactive
  substances, mercury,  benzene, boron, and heavy metals
Malnutrition and anemia.
Excessive stress!
Modifying these behaviors can improve a man’s fertility and should be considered when a couple is trying to achieve pregnancy.
Hormonal Problems
A small percentage of male infertility is caused by hormonal problems.  The hypothalamus-pituitary endocrine system regulates the chain of hormonal events that enables testes to produce and effectively disseminate sperm.
The following is a list of hormonal disorders which can disrupt male infertility:
Hyperprolactinemia:Elevated prolactin–a hormone associated with nursing mothers, is found in 10 to 40 percent of infertile males.  Mild elevation of prolactin levels produces no symptoms, but greater elevations of the hormone reduces sperm production, reduces libido and may cause impotence.  This condition responds well to the drug Parlodel (bromocriptine).
Hypothyroidism:Low thyroid hormone levels–can cause poor semen quality, poor testicular function and may disturb libido.  May be caused by a diet high in iodine.  Reducing iodine intake or beginning thyroid hormone replacement therapy can elevate sperm count.  This condition is found in only 1 percent of infertile men.
Congenital Adrenal Hyperplasia:Occurs when the pituitary is suppressed by increased levels of adrenal androgens.  Symptoms include low sperm count, an increased number of immature sperm cells, and low sperm cell motility.  Is treated with cortisone replacement therapy.  This condition is found in only 1 percent of infertile men.
Hypogonadotropic Hypopituitarism:Low pituitary gland output of LH and FSH.  This condition arrests sperm development and causes the progressive loss of germ cells from the testes and causes the seminiferous tubules and Leydig (testosterone producing) cells to deteriorate.  May be treated with the drug Serophene.  However, if all germ cells are destroyed before treatment commences, the male may be permanently infertile.
Panhypopituitafism:Complete pituitary gland failure–lowers growth hormone, thyroid-stimulating hormone, and LH and FSH levels.  Symptoms include:  lethargy, impotence, decreased libido, loss of secondary sex characteristics, and normal or undersized testicles.  Supplementing the missing pituitary hormones may restore vigor and a hormone called hCG may stimulate testosterone and sperm production.
Physical Problems
A variety of physical problems can cause male infertility.  These problems either interfere with the sperm production process or disrupt the pathway down which sperm travel from the testes to the tip of the penis.  These problems are usually characterized by a low sperm count and/or abnormal sperm morphology.  The following is a list of the most common physical problems that cause male infertility:
Varicocele:
A varicocele is an enlargement of the internal spermatic veins that drain blood from the testicle to the abdomen (back to the heart) and are present in 15% of the general male population and 40% of infertile men.  These images show what a variocoele looks like externally and internally.
A varicocele develops when the one way valves in these spermatic veins are damaged causing an abnormal back flow of blood from the abdomen into the scrotum creating a hostile environment for sperm development.  Varicocoeles may cause reduced sperm count and abnormal sperm morphology which cause infertility.  Variococles can usually be diagnosed by a physical examination of the scrotum which can be aided by the Doppler stethoscope and scrotal ultrasound.  Varicocoele can be treated in many ways (see treatment section), but the most successful treatments involve corrective surgery.
Damaged Sperm Ducts:
Seven percent of infertile men cannot transport sperm from their testicles to out of their penis.  This pathway may be blocked by a number of conditions:
A genetic or developmental mistake may block or cause the absence of one or both tubes (which
  transport the sperm from the testes to the penis).
Scarring from tuberculosis or some STDs may block the epididymis or tubes.
An elective or accidental vasectomy may interrupt tube continuity.
Torsion:
Is a common problem affecting fertility that is caused by a supportive tissue abnormality which allows the testes to twist inside the scrotum which is characterized by extreme swelling.  Torsion pinches the blood vessels that feed the testes shut which causes testicular damage.  If emergency surgery is not performed to untwist the testes, torsion can seriously impair fertility and cause permanent infertility if both testes twist.
Infection and Disease:
Mumps, tuberculosis, brucellosis, gonorrhea, typhoid, influenza, smallpox, and syphilis can cause testicular atrophy.  A low sperm count and low sperm motility are indicators of this condition.  Also, elevated FSH levels and other hormonal problems are indicative of testicular damage.  Some STDs like gonorrhea and chlamydia can cause infertility by blocking the epididimis or tubes.  These conditions are usually treated by hormonal replacement therapy and surgery in the case of tubular blockage.
Klinefelter’s Syndrome:
Is a genetic condition in which each cell in the human body has an additional X chromosome–men with Klinefelter’s Syndrome have one Y and two X chromosomes.  Physical symptoms include peanut-sized testicles and enlarged breasts.  A chromosome analysis is used to confirm this analysis.  If this condition is treated in its early stages (with the drug hCG), sperm production may commence and/or improve.  However, Klinefelter’s Syndrome eventually causes all active testicular structures to atrophy.  Once testicular failure has occurred, improving fertility is impossible.
Retrograde Ejaculation:
Is a condition in which semen is ejaculated into the bladder rather than out through the urethra because the bladder sphincter does not close during ejaculation.  If this disorder is present, ejaculate volume is small and urine may be cloudy after ejaculation.  This condition affects 1.5 percent of infertile men and may be controlled by medications like decongestants which contract the bladder sphincter or surgical reconstruction of the bladder neck can restore normal ejaculation.
Psychological/Physical/Behavioral Problems:
Several sexual problems exist that can affect male fertility.  These problems are most often both psychological and physical in nature:  it is difficult to separate the physiological and physical components.
Erectile Disfunction (ED):
Also known as impotence, this condition is common and affects 20 million American men.  ED is the result of a single, or more commonly a combination of multiple factors.  In the past, ED was thought to be the result of psychological problems, but new research indicates that 90 percent of cases are organic in nature.  However, most men who suffer from ED have a secondary psychological problem that can worsen the situation like performance anxiety, guilt, and low self-esteem.  Many of the common causes of impotence include:  diabetes, high blood pressure, heart and vascular disease, stress, hormone problems, pelvic surgery, trauma, venous leak, and the side effects of frequently prescribed medications (i.e. Prozac and other SSRIs, Propecia).  Luckily, many treatment options exist for ED depending on the cause–these will be discussed in the treatment section.
Premature Ejaculation:
Is defined as an inability to control the ejaculatory response for at least thirty seconds following penetration.  Premature ejaculation becomes a fertility problem when ejaculation occurs before a man is able to fully insert his penis into his partner’s vagina.  Premature ejaculation can be overcome by artificial insemination or by using a behavioral modification technique called the “squeeze technique” which desensitizes the penis.
Ejaculatory Incompetence:
This rare psychological condition prevents men from ejaculating during sexual intercourse even though they can ejaculate normally through masturbation.  This condition sometimes responds well to behavioral therapy; if this technique does not work, artificial insemination can be employed using an ejaculate from masturbation.