A number of things can cause impaired sperm count, mobility, or impaired ability to fertilize the egg. The most common causes of male infertility include abnormal sperm production or function, impaired delivery of sperm, general health and lifestyle issues, and overexposure to certain environmental elements.

Abnormal Sperm Parameters

Most cases of male factor infertility are due to problems with the sperm. The number of reasons and causes include:

Low Sperm Concentration
A normal sperm concentration is greater than or equal to 20 million sperm per milliliter of semen. A count of 10 million or fewer sperm per milliliter of semen indicates low sperm concentration (sub-fertility). A count of 40 million sperm or higher per milliliter of semen indicates increased fertility. Complete failure of the testicles to produce sperm is rare, affecting very few infertile men. Blockages of the outflow tube (the vas deferens) can also reduce or completely block the passage of sperm, resulting in low to non-existent concentrations.

Impaired Shape And Movement Of Sperm
Sperm must be properly shaped and able to move rapidly and accurately toward the egg for fertilization to occur. If the shape and structure (morphology) of the sperm are abnormal or the movement (motility) is impaired, sperm may not be able to reach or penetrate the egg. Very poor morphology is associated with much higher rates of damaged DNA (the genetic coding material) within the sperm.

Infections
Infection may temporarily affect sperm motility. Repeated bouts of sexually transmitted diseases (STDs), such as chlamydia and gonorrhea, are most often associated with male infertility. These infections can cause scarring and block sperm passage. If mumps, a viral infection usually affecting young children, occurs after puberty, inflammation of the testicles can impair sperm production. Inflammation of the prostate (prostatitis), urethra or epididymis also may alter sperm motility. Other severe viral and bacterial infections have also been suspected to cause male infertility, although the cases are usually rare and isolated.

Undescended Testicle
Undescended testicle occurs when one or both testicles fail to descend from the abdomen into the scrotum during fetal development. Because the testicles are exposed to the higher internal body temperature, compared with the temperature in the scrotum, sperm production may be affected.

Varicocele
A varicocele is a varicose vein in the scrotum that may prevent normal cooling of the testicle, leading to reduced sperm count and motility. The most recent clinical data suggests that the larger varicoceles are the biggest trouble makers: no surprise there!

Genetic Defects
In the genetic defect Klinefelter's syndrome, a man has two X chromosomes and one Y chromosome instead of one X and one Y. This causes abnormal development of the testicles, resulting in low or absent sperm production and possibly low testosterone. There are also numerous other genetic conditions that can impair male fertility. Some genetic conditions are absolutely untreatable, some are able to be overcome with advanced reproductive technologies.

Testosterone Deficiency (Male Hypogonadism)
Infertility can result from disorders of the testicles themselves, or an abnormality affecting the hypothalamus or pituitary gland in the brain that produces the hormones that control the testicles. This does not mean that giving testosterone will improve male fertility! Taking testosterone actually has the opposite effect. Do not try to treat testosterone deficiency yourself -- see a professional.

Unexplained Male Factor Infertility Related To Sperm
In many instances, no cause for reduced sperm production is found. When sperm concentration is less than 5 million per milliliter of semen, genetic causes could be involved. A blood test can reveal whether there are subtle changes in the Y chromosome or hormonal imbalances present that are not mentioned above.

Delivery Problems

There may also be problems with the delivery of sperm from the penis into the vagina that can result in infertility. These may include:

Retrograde Ejaculation
This occurs when semen enters the bladder during orgasm rather than emerging out through the penis. Various conditions can cause retrograde ejaculation including diabetes, bladder, prostate or urethral surgery, and the use of certain medications.

Sexual Issues
Often treatable, problems with sexual intercourse or technique may affect fertility. Difficulties with erection of the penis (erectile dysfunction), premature ejaculation, painful intercourse (dyspareunia), or psychological or relationship problems can contribute to infertility. Use of lubricants such as oils or petroleum jelly can be toxic to sperm and impair fertility.

No Semen
The absence of ejaculate may occur in men with spinal cord injuries or diseases. This fluid carries the sperm from the penis into the vagina.

Misplaced Urinary Opening (Hypospadias)
A birth defect can cause the urinary (urethral) opening to be abnormally located on the underside of the penis. If not surgically corrected, this condition can prevent sperm from reaching the woman's cervix.

Blockage Of Epididymis (Ejaculatory Ducts)
Some men are born with blockage of the part of the testicle that contains sperm (epididymis) or ejaculatory ducts. Some men lack the tube that carries sperm (vas deferens) from the testicle out to the opening in the penis. Absent vas deferens may be seen in men with unrecognized cystic fibrosis.

Cystic Fibrosis
Men with cystic fibrosis often have missing or obstructed vas deferens.

Anti-sperm Antibodies
Antibodies that target sperm and weaken or disable them usually occur after surgical blockage of part of the vas deferens for male sterilization (vasectomy). Presence of these antibodies may complicate the effectiveness of the sperm after the microsurgical reversal of a vasectomy.

Lifestyle Factors

In addition to infertility related to issues of the sperm, a man's general health and lifestyle may affect fertility. Some common causes of infertility related to health and lifestyle include:

Obesity
Increased body mass may be associated with fertility problems in men. Obesity creates relatively high levels of the female-associated hormone estrogen, and has obvious bad influences on sexual performance.

Malnutrition
Deficiencies in nutrients such as protein, vitamin C, selenium, zinc and folate may contribute to infertility. All men trying to conceive should consider eating like a "cave man" to include meat and vegetables every day.

Alcohol And Drugs
Alcohol or drug dependency can be associated with poor health and reduced fertility. The use of certain drugs also can contribute to infertility. Anabolic steroids, for example, which are taken to stimulate muscle strength and growth, can cause the testicles to shrink and sperm production to decrease. Use of cocaine or marijuana may temporarily reduce the number and quality of your sperm.

Alcohol should be moderately consumed. Two drinks a day are probably OK as long as there are no other health reasons to be completely abstinent. Men should avoid getting drunk for as long as they are trying to impregnate their partners.

Men who smoke may have a lower sperm count than do those who don't smoke. Chewing tobacco is particularly harmful to sperm.

Emotional Stress Or Chronic Pain
Stress may interfere with certain hormones needed to produce sperm. Your sperm count may be affected if you experience excessive or prolonged emotional stress. A problem with fertility itself can sometimes become long term and discouraging, producing more stress. Infertility can affect social relationships and sexual functioning. Chronic painful conditions or illnesses also raise stress hormones and can significantly harm fertility.

Cancer And Its Treatment
Both radiation and chemotherapy treatment for cancer can impair sperm production, sometimes severely. The closer radiation treatment is to the testicles, the higher the risk of infertility. Removal of one or both testicles due to cancer also may affect male fertility. Men anticipating cancer treatments will frequently make several treatments to the sperm bank before undergoing toxic treatments.

Other Medical Conditions
A severe injury or major surgery can affect male fertility. Certain diseases or conditions, such as diabetes, thyroid disease, Cushing's syndrome, or anemia may be associated with infertility.

Age
A gradual decline in fertility is common in men older than 35. This decline is much less severe than that seen in women, and this is generally a rare issue.

Environmental Hazards
Lastly, exposure to environmental hazards may affect fertility. Over-exposure to certain environmental elements such as heat, toxins and chemicals can reduce sperm count either directly by affecting testicular function or indirectly by altering the male hormonal system. Specific causes include:

Pesticide And Chemical Exposure
Herbicides and insecticides may cause female hormone-like effects in the male body and may be associated with reduced sperm production and testicular cancer. Lead exposure may also cause infertility.

Overheating The Testicles
Frequent use of saunas or hot tubs can elevate your core body temperature. This may impair your sperm production and lower your sperm count. Long-haul truckers frequently have quite depressed semen parameters; this may be due to the fact that they sit in constrained positions in hot cabs for long time periods.