The most common cause of male infertility is low sperm count. Absence of sperm in the semen is less common, affecting only 1% of all men and 10% to 15% of infertile men.¹

Causes of sperm count problems include:

• Hormonal problems in the testicles or pituitary gland. The pituitary gland releases hormones that stimulate the testicles to produce testosterone.
• Testicular injury or failure, either present at birth (congenital) or associated with radiation or toxic chemical exposure.
• Cancer treatment with certain kinds of chemotherapy or radiation.
• Antibodies that attack sperm and that also may be present in semen. Sperm antibodies sometimes develop when a man's sperm has been exposed to his immune system (outside of the testicles). This may happen after a vasectomy, an infection, or an injury to the testicles.²
• Drug use (some prescription medications, and marijuana and tobacco use).
• Structural problems. These include:
  • A varicocele in the testicles.
  • Blocked ejaculation due to a surgical vasectomy.
  • Absence of a vas deferens (a birth defect that may be associated with the cystic fibrosis genes).
  • Retrograde ejaculation (the ejaculation of semen into the bladder rather than out through the penis).
• Chromosomal problems (such as Klinefelter syndrome).
• Genetic problems.

See an illustration of the male reproductive system.