These are the common causes of male infertility:
Blocked Sperm Ducts
The causes of male infertility are often more difficult to define. Blockage of the sperm ducts is one obvious cause. Generalized blockage may be caused by sexually transmitted diseases. More easily identifiable blockage is caused by a vasectomy (voluntary surgery to occlude the sperm ducts for birth control purposes). While it is usually possible to surgically reconnect the tubes after vasectomy, some men, especially those who underwent the procedure more than 10 years earlier, remain infertile because in the interim their systems have developed an immune reaction that results in the production of antibodies that destroy or immobilize their own sperm.
Another common cause of male infertility is a varicocele, a collection of dilated veins around the testicles that hinders sperm function by increasing body temperature in the scrotum. In order for the testicles to produce healthy sperm, the temperature in the scrotum must be lower than it is in the rest of the body.
Abnormalities of the Testicles
Ideally, the testicles should have descended into the scrotum shortly after birth, but in some cases they do not reach the scrotum for years. In such circumstances, it may be necessary to accomplish this surgically when the man is very young to prevent the testicles from becoming severely damaged, thereby resulting in infertility. In rare cases, abnormal development of the testicles and/or sperm ducts may result from injury, disease or hereditary abnormalities.
Certain drugs or chemicals in the environment may also inhibit sperm production and function. And as in women, drugs such as DES can also produce abnormalities in the male offspring's reproductive system.
Finally, for reasons that are often not readily apparent, some men lack the adequate hormonal stimulation that is required for proper sperm production.