Infertility is different from sterility. Being sterile means you will never ever conceive a child. With sterility, you or your partner has a physical problem that precludes the ability to conceive. A diagnosis of infertility simply means that becoming pregnant may be a challenge rather than an impossibility.

Causes of male infertility
There are a number of causes for male infertility which can result in impaired sperm count or 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, conditions related to a man's general health and lifestyle, and overexposure to extreme environment:

Abnormal sperm production or function. Most cases of male infertility are due to sperm abnormalities, such as:

• 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 the egg.
• Absent sperm production in testicles. Complete failure of the testicles to produce sperm is rare, affecting very few infertile men.
• 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 (subfertility). A count of 40 million sperm or higher per milliliter of semen indicates increased fertility.
• Varicocele. A varicocele is a varicose vein in the scrotum that may prevent normal cooling of the testicle and raise testicular temperature, preventing sperm from surviving.
• Undescended testicle (cryptorchidism). This occurs when one or both testicles fail to descend from the abdomen into the scrotum during fetal development. Undescended testicles can cause mild to severely impaired sperm production. Because the testicles are exposed to the higher internal body temperature compared to the temperature in the scrotum, sperm production may be affected.
• Testosterone deficiency (male hypogonadism). Infertility can result from disorders of the testicles themselves, or an abnormality affecting the hypothalamus or pituitary glands in the brain that produce the hormones that control the testicles.
• Klinefelter's syndrome. In this disorder of the sex chromosomes, 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. Testosterone production also may be lower.
• 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. Mycoplasma is an organism that may fasten itself to sperm cells, making them less motile. 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.