Overview

The most common cause of male infertility is low sperm count. Absence of sperm in the semen is less common, affecting 1 out of 100 men and affecting 10 to 15 out of 100 infertile men.^{footnote 1}

Causes of sperm count problems include:

• Hormonal problems in the testicles, Opens dialog or pituitary gland, Opens dialog. The pituitary gland releases hormones that stimulate the testicles to produce testosterone, Opens dialog.
• 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, Opens dialog 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.^{footnote 2}
• Drug use (some prescription medicines, and marijuana and tobacco use).
• Structural problems. These include:
  • A varicocele, Opens dialog in the testicles.
  • Blocked ejaculation due to a surgical vasectomy, Opens dialog.
  • Absence of a vas deferens, Opens dialog (a birth defect that may be associated with the cystic fibrosis, Opens dialog genes).
  • Retrograde ejaculation (the ejaculation of semen into the bladder rather than out through the penis).
• Chromosomal problems (such as Klinefelter syndrome, Opens dialog).
• Genetic problems.

See a picture of the male reproductive system, Opens dialog.