The most common cause of male infertility is a varicocele. A varicocele is made up of enlarged veins in the scrotum (the skin “sack” that hangs beneath the penis) on 1 or both sides. The veins make the inside of the scrotum warmer and can reduce sperm production by the testicle on the same side.
Other causes of male infertility include:
- A blockage in a man’s reproductive system
- Certain medicines
- Low sperm count
- Sperm that are abnormally shaped or that don’t move correctly
- Undescended testicles
- An underlying medical problem
Other factors that may affect fertility include tobacco smoking, excessive alcohol consumption and abuse of other illegal drugs, emotional stress, obesity and age (fertility gradually decreases in men who are older than 35). Sometimes the cause of male infertility cannot be identified. In these cases, there may be an underlying genetic problem.