Causes for male infertility (low sperm count) include tight-fitting jeans and underwear that heat the scrotum and testes, thereby inhibiting sperm production. Very hot baths may hasten the death of sperm. Environmental pollution from cigarette smoke, heavy metals (lead, mercury, arsenic), pesticides, solvents, toxic chemicals, aflatoxin (a fungus found on peanuts and grains), and synthetic estrogens in poultry and dairy feed all interfere with sperm formation and protection. In a study of 100 males, aflatoxin levels in infertile men were 60% higher than in fertile men. Marginal zinc status is associated with poor sperm count and motility (especially if testosterone levels are low). Zinc supplementation improves both sperm count and testosterone levels.

Another cause of male infertility is the presence of a varicocele.

Varicocele is a mass of enlarged veins that develops in the spermatic cord, which leads from the testicles (testes ) up through a passageway in the lower abdominal wall (systeminguinal canal) to the circulatory system. The spermatic cord is made up of blood vessels, lymphatic vessels, nerves, and the duct that carries sperm from the body (vas deferens). If the valves that regulate bloodflow from these veins become defective, blood does not circulate out of the testicles efficiently, which causes swelling in the veins above and behind the testicles.

A varicocele can develop in one testicle or both, but in about 85% of cases it develops in the left testicle. A one-sided (unilateral) varicocele can affect either testicle. Because of the impaired circulation of blood created by a varicocele, the blood does not cool as it does normally. The increased temperature of the blood raises the temperature of the testes, which is believed to contribute to infertility, as heat can damage or destroy sperm. The increased temperature may also impede production of new, healthy sperm.

Incidence of varicocele is 10-20% and is highest in men between the ages of 15 and 25. The sudden appearance of varicocele in an older man may indicate a renal tumor blocking the spermatic vein. Approximately 40% of infertile men have a varicocele and among men with secondary infertilit (those who have fathered a child but are no longer able to do so) prevalence may be as high as 80%.

Physical support with snug-fitting underwear may alleviate symptoms, if infertility is not an issue. Otherwise, some form of surgery will be required to remove the mass of enlarged veins.