Inside the scrotum are veins that provide blood flow to the testicles, and when one of those veins becomes enlarged, it’s called a varicocele. Experienced by roughly 15 percent of men, varicoceles are similar to varicose veins, which are also essentially harmless.

While varicoceles are relatively common, their typical lack of symptoms makes them difficult to detect. Generally, they’re more likely to be found when a doctor is investigating a different reproductive issue, such as infertility.

A varicocele causes the temperature to increase in the scrotum, which must be at least two degrees cooler than the body for proper levels of sperm production. While medical science has an imperfect understanding of the relationship between varicoceles and infertility, it has long been known that elevated testicular temperature kills sperm.