Why does a man become infertile?

The most common cause for male infertility is a problem with the sperm - either low sperm count or sperm with poor quality. Sperm with poor quality cannot move rapidly enough or in the right direction, or may be abnormally shaped. Some conditions that may contribute to sperm problems include:

• Under-developed testes-usually arising after a mumps infection, a hernia surgery, an injury or birth defect.
• Swollen veins in the scrotum.
• Undescended testes-a problem often present from birth in which the testes remain in the body cavity. Normally they descend into the scrotum before birth.
• Infections, such as gonorrhea or tuberculosis, that block the ducts through which the sperm travel.
• Exposure to metals such as leads, or chemicals such as pesticides.
• Certain medications, such as Tagamet (cimetidine), Dilantin (phenytoin), Folex (methotrexate), Axulfidine (sulfasalazine), corticosteroids and chemotherapy drugs such as Cytoxan and Neosar (cyclophosphamide).
• Injury to the testicles
• Chronic prostate infections

Other common causes of male infertility are:

• Autoimmunity, in which antibodies or cells of the man's immune system attack sperm cells, mistaking them for toxic invaders. The antibodies attach themselves to the sperm and may cause them to stick together, or may stop them from penetrating the cervical mucous or the egg.

  Nice To Know: What causes male autoimmunity? Male autoimmunity often develops after vasectomy. Sperm actually are produced after a vasectomy, but may leak out into the body where immune cells target them as invaders. Even when a vasectomy is reversed through surgery, this autoimmunity may continue. Antibodies to sperm have also been located in men without vasectomies-in about 10 percent of infertile men. In these cases, the reason for the existence of these antibodies is often unknown.

• Retrograde ejaculation. In retrograde ejaculation the muscles of the urethra do not force the sperm out. Instead, the sperm travel backward into the bladder. Causes of retrograde ejaculation include:
• Drugs such as tranquilizers or high blood pressure medicines.
• Diseases such as diabetes or multiple sclerosis.
• Neck, bladder or prostate surgery.
• Spinal cord injury.

In a small percentage of cases, male infertility is caused by:

• Sexual difficulties such as impotence, premature ejaculation, or painful intercourse. These problems can often be easily treated.

• Genetic defects or structural problems. In germ-cell aplasia, for instance, the sperm-producing germ cells do not develop correctly. Defects in the Y chromosome or in certain genes may also play a part in infertility.

Rarely, a hormonal difficulty that decreases or stops the man's production of sperm. Hormonal problems may be present from birth or can develop from brain or pituitary gland tumors or radiation treatment. Sometimes, hormonal difficulties are induced by excessive exercise, malnutrition or other illnesses.