Male infertility is known to be a contributory factor in about half the couples facing fertility problems. The list of male infertility problems is increasing with the recent addition being environmental factors that have been recognized to cause male infertility.

Male infertility problems stem from to the following causes:

Testicular causes: The testis is the site where the sperms are produced. Normally the testis is placed outside the body in the scrotal sac, yet in some subjects due to a developmental delay the testes may not descend into the testicular sac and remain in the groin. This condition is called as cryptorchidism or undescended testes. Such organs are likely to have reduced spermatogenesis due to the increased temperature within the testes. Other testicular causes contributing to male infertility are varicocoeles and tumors. Abnormal sperm number, morphology and function are also important causes of male infertility. Some infections like mumps virus infections can cause inflammation of the testes leading to infertility.
Blocked ejaculatory ducts: Sometimes due to infections or injury the tubes that carry the sperms from the testes to the urethra may get blocked leading to azoospermia i.e. absence of sperms. In such cases a biopsy of the testis is able to differentiate between blocked tubes or a testicular failure to be the cause of infertility.
Abnormal sexual function: Erectile dysfunction is a common cause of male infertility. Abnormal sexual function may be due to weak contractility of the penile muscles or due to decreased stimulation of the pelvic nerve plexus which is important for erection. Sometimes the reason is likely to be purely psychological. Medical as well as surgical therapy is available for the treatment of erectile dysfunction in males.
Hormonal: Hormones from the pituitary as well as the testes play an important role in spermatogenesis. The Leutinizing hormone (LH), Follicle Stimulating Hormone (FSH) and testosterone are the main hormones involved in male reproduction. An increase in the hormone estrogen causes a decrease in FSH and LH thereby reducing testosterone production and spermatogenesis.
Genetic: Sex chromosome disorders like Klinefelter’s syndrome, Noonan’s syndrome are linked with hypogonadism. This type of male infertility may be the most difficult to treat.
Drugs: Cytotoxic drugs used in the treatment of cancers destroy the actively dividing sperm cells in the testes to cause infertility. Though this type of infertility is temporary, the return of fertility is likely to be only after one year of stopping the chemotherapy. Anabolic steroids often used for muscle building reduce male fertility by inhibiting the male hormone. Estrogen like drugs may also act similarly causing temporary infertility. Other recreational drugs like marihuana, alcohol , opiates etc also affect male fertility.
Environmental: Environmental pollution due to toxins like alkyl phenols, phthalates, dioxins, organochlorine pesticides etc are contributory factors to male infertility. In addition radiation is also known to impair male fertility. A radiation dose of >600 rads is capable of producing permanent infertility in males. Temporary infertility may be seen for about 6 months with doses < or = 100 rads.