Low sperm count is an uncomfortable subject for some men to discuss, which may be why so many urban legends have sprung up about its causes.
While many grow up hearing that drinking Mountain Dew or shunning boxers can create barriers to fatherhood later on, studies haven't backed up those claims.
Meanwhile, a lesser-known condition that needs a doctor's diagnosis often goes overlooked.
"The most common treatable cause of male factor infertility is called varicocele," said Dr. Dan Williams, director of male reproductive medicine and surgery at the University of Wisconsin School of Medicine and Public Health.
Varicocele is a condition where varicose veins surround the testicle, typically the left one. Although the exact mechanism is unknown, Williams said the most widely accepted theory is that the varicocele increases the heat around the testicle.
"After we repair a varicocele, scrotal temperature decreases," he explained. Doctors don't know what causes varicoceles, but they are easily treatable and can only be diagnosed by a doctor.
"This is another reason it's very important for men to be evaluated by a urologist who's specially trained in male infertility," said Williams, noting that the common route of the man being evaluated by his primary care doctor or his partner's OB/GYN is often not enough.
"Just because they have sperm doesn't mean that there's not something harmful or treatable that we can diagnose that can help us to improve the sperm counts," he said.
In his own clinic at the University of Wisconsin, Williams notes, couples are screened together, with the woman seeing an OB/GYN and the man seeing a urologist.
"Couples are evaluated for male and female factor infertility issues simultaneously," he said. "Fertility really is a couples thing not just a male or a female thing."
But when it comes to figuring out on your own how to avoid infertility, what you hear can be misleading.
"The problem with a lot of these studies is there's something being reported in the medical news every single day, and often they're contradictory," said Dr. Abraham Morgentaler, associate clinical professor of urology at Harvard Medical School and Beth Israel Deaconess Medical Center and author of "Testosterone for Life." "In general, if there's something that makes a really big difference, the data are consistent and they'll show up often in a variety of studies under a variety of different conditions."
He notes that a lot of myths circulate around diet and fertility, but some of those have weak data and others show effects in animals that have not been replicated in humans. What he tells patients, Morgentaler said, is his fertility motto: "Live clean, stay cool. I think that's important."
"The point is that heat is a definite, no questions asked, has an impact on sperm production. And the live clean is that we know a number of recreational drugs appear to have some impact on fertility," he explained.
In the following pages, we see which alleged sperm-killers are culprits to avoid and which don't have evidence showing them to be all that harmful. Still, all couples with fertility troubles would do well to seek out a professional opinion.
"Most doctors now laugh that one off," said Morgentaler.